Merge pull request 'K2V PollRange, version 2' (#471) from k2v-watch-range-2 into main

Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/471

23 files changed, 1125 insertions, 198 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 0515801c..48316436 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1828,12 +1828,13 @@ dependencies = [
 
 [[package]]
 name = "k2v-client"
-version = "0.0.1"
+version = "0.1.1"
 dependencies = [
  "base64 0.21.0",
  "clap 4.1.3",
  "garage_util",
  "http",
+ "hyper-rustls 0.23.2",
  "log",
  "rusoto_core",
  "rusoto_credential",
diff --git a/Cargo.nix b/Cargo.nix
index 35a4e176..90535d4a 100644
--- a/Cargo.nix
+++ b/Cargo.nix
@@ -32,7 +32,7 @@ args@{
   ignoreLockHash,
 }:
 let
-  nixifiedLockHash = "cf836c01a9c668bab5f9a09d468f47aa24c50abec92855503624d706721335ef";
+  nixifiedLockHash = "8681b26e2f98ae495ad3ac0d6df1241a6bc0f06bd5fa7ae4c08d8cc13b5b88c5";
   workspaceSrc = if args.workspaceSrc == null then ./. else args.workspaceSrc;
   currentLockHash = builtins.hashFile "sha256" (workspaceSrc + /Cargo.lock);
   lockHashIgnored = if ignoreLockHash
@@ -65,7 +65,7 @@ in
     garage_api = rustPackages.unknown.garage_api."0.8.1";
     garage_web = rustPackages.unknown.garage_web."0.8.1";
     garage = rustPackages.unknown.garage."0.8.1";
-    k2v-client = rustPackages.unknown.k2v-client."0.0.1";
+    k2v-client = rustPackages.unknown.k2v-client."0.1.1";
   };
   "registry+https://github.com/rust-lang/crates.io-index".addr2line."0.19.0" = overridableMkRustCrate (profileName: rec {
     name = "addr2line";
@@ -2539,9 +2539,9 @@ in
     };
   });
   
-  "unknown".k2v-client."0.0.1" = overridableMkRustCrate (profileName: rec {
+  "unknown".k2v-client."0.1.1" = overridableMkRustCrate (profileName: rec {
     name = "k2v-client";
-    version = "0.0.1";
+    version = "0.1.1";
     registry = "unknown";
     src = fetchCrateLocal (workspaceSrc + "/src/k2v-client");
     features = builtins.concatLists [
@@ -2554,6 +2554,7 @@ in
       ${ if rootFeatures' ? "k2v-client/clap" || rootFeatures' ? "k2v-client/cli" then "clap" else null } = (rustPackages."registry+https://github.com/rust-lang/crates.io-index".clap."4.1.3" { inherit profileName; }).out;
       ${ if rootFeatures' ? "k2v-client/cli" || rootFeatures' ? "k2v-client/garage_util" then "garage_util" else null } = (rustPackages."unknown".garage_util."0.8.1" { inherit profileName; }).out;
       http = (rustPackages."registry+https://github.com/rust-lang/crates.io-index".http."0.2.8" { inherit profileName; }).out;
+      hyper_rustls = (rustPackages."registry+https://github.com/rust-lang/crates.io-index".hyper-rustls."0.23.2" { inherit profileName; }).out;
       log = (rustPackages."registry+https://github.com/rust-lang/crates.io-index".log."0.4.17" { inherit profileName; }).out;
       rusoto_core = (rustPackages."registry+https://github.com/rust-lang/crates.io-index".rusoto_core."0.48.0" { inherit profileName; }).out;
       rusoto_credential = (rustPackages."registry+https://github.com/rust-lang/crates.io-index".rusoto_credential."0.48.0" { inherit profileName; }).out;
diff --git a/doc/drafts/k2v-spec.md b/doc/drafts/k2v-spec.md
index 9d41b2c0..faa1a247 100644
--- a/doc/drafts/k2v-spec.md
+++ b/doc/drafts/k2v-spec.md
@@ -706,6 +706,73 @@ HTTP/1.1 200 OK
 ]
 ```
 
+**PollRange: `POST /<bucket>/<partition key>?poll_range`**, or alternatively<br/>
+**PollRange: `SEARCH /<bucket>/<partition key>?poll_range`**
+
+Polls a range of items for changes.
+
+The query body is a JSON object consisting of the following fields:
+
+| name            | default value | meaning                                                                                |
+|-----------------|---------------|----------------------------------------------------------------------------------------|
+| `prefix`        | `null`        | Restrict items to poll to those whose sort keys start with this prefix                 |
+| `start`         | `null`        | The sort key of the first item to poll                                                 |
+| `end`           | `null`        | The sort key of the last item to poll (excluded)                                       |
+| `timeout`       | 300           | The timeout before 304 NOT MODIFIED is returned if no value in the range is updated    |
+| `seenMarker`    | `null`        | An opaque string returned by a previous PollRange call, that represents items already seen |
+
+The timeout can be set to any number of seconds, with a maximum of 600 seconds (10 minutes).
+
+The response is either:
+
+- A HTTP 304 NOT MODIFIED response with an empty body, if the timeout expired and no changes occurred
+
+- A HTTP 200 response, indicating that some changes have occurred since the last PollRange call, in which case a JSON object is returned in the body with the following fields:
+
+| name            | meaning                                                                                |
+|-----------------|----------------------------------------------------------------------------------------|
+| `seenMarker`    | An opaque string that represents items already seen for future PollRange calls         |
+| `items`         | The list of items that have changed since last PollRange call, in the same format as ReadBatch |
+
+If no seen marker is known by the caller, it can do a PollRange call
+without specifying `seenMarker`. In this case, the PollRange call will
+complete immediately, and return the current content of the range (which
+can be empty) and a seen marker to be used in further PollRange calls. This
+is the only case in which PollRange might return an HTTP 200 with an empty
+set of items.
+
+A seen marker returned as a response to a PollRange query can be used for further PollRange
+queries on the same range, or for PollRange queries in a subrange of the initial range.
+It may not be used for PollRange queries on ranges larger or outside of the initial range.
+
+Example query:
+
+```json
+SEARCH /my_bucket?poll_range HTTP/1.1
+
+{
+  "prefix": "0391.",
+  "start": "0391.000001973107",
+  "seenMarker": "opaquestring123",
+}
+```
+
+
+Example response:
+
+```json
+HTTP/1.1 200 OK
+Content-Type: application/json
+
+{
+  "seenMarker": "opaquestring456",
+  "items": [
+    { sk: "0391.000001973221", ct: "opaquetoken123", v: ["b64cryptoblob123", "b64cryptoblob'123"] },
+    { sk: "0391.000001974191", ct: "opaquetoken456", v: ["b64cryptoblob456", "b64cryptoblob'456"] },
+  ]
+}
+```
+
 
 ## Internals: causality tokens
 
diff --git a/src/api/k2v/api_server.rs b/src/api/k2v/api_server.rs
index 084867b5..bb85b2e7 100644
--- a/src/api/k2v/api_server.rs
+++ b/src/api/k2v/api_server.rs
@@ -164,6 +164,9 @@ impl ApiHandler for K2VApiServer {
 			Endpoint::InsertBatch {} => handle_insert_batch(garage, bucket_id, req).await,
 			Endpoint::ReadBatch {} => handle_read_batch(garage, bucket_id, req).await,
 			Endpoint::DeleteBatch {} => handle_delete_batch(garage, bucket_id, req).await,
+			Endpoint::PollRange { partition_key } => {
+				handle_poll_range(garage, bucket_id, &partition_key, req).await
+			}
 			Endpoint::Options => unreachable!(),
 		};
 
diff --git a/src/api/k2v/batch.rs b/src/api/k2v/batch.rs
index 82b4f7e3..26d678da 100644
--- a/src/api/k2v/batch.rs
+++ b/src/api/k2v/batch.rs
@@ -5,7 +5,6 @@ use hyper::{Body, Request, Response, StatusCode};
 use serde::{Deserialize, Serialize};
 
 use garage_util::data::*;
-use garage_util::error::Error as GarageError;
 
 use garage_table::{EnumerationOrder, TableSchema};
 
@@ -26,11 +25,7 @@ pub async fn handle_insert_batch(
 
 	let mut items2 = vec![];
 	for it in items {
-		let ct = it
-			.ct
-			.map(|s| CausalContext::parse(&s))
-			.transpose()
-			.ok_or_bad_request("Invalid causality token")?;
+		let ct = it.ct.map(|s| CausalContext::parse_helper(&s)).transpose()?;
 		let v = match it.v {
 			Some(vs) => DvvsValue::Value(
 				BASE64_STANDARD
@@ -68,10 +63,7 @@ pub async fn handle_read_batch(
 		resps.push(resp?);
 	}
 
-	let resp_json = serde_json::to_string_pretty(&resps).map_err(GarageError::from)?;
-	Ok(Response::builder()
-		.status(StatusCode::OK)
-		.body(Body::from(resp_json))?)
+	Ok(json_ok_response(&resps)?)
 }
 
 async fn handle_read_batch_query(
@@ -163,10 +155,7 @@ pub async fn handle_delete_batch(
 		resps.push(resp?);
 	}
 
-	let resp_json = serde_json::to_string_pretty(&resps).map_err(GarageError::from)?;
-	Ok(Response::builder()
-		.status(StatusCode::OK)
-		.body(Body::from(resp_json))?)
+	Ok(json_ok_response(&resps)?)
 }
 
 async fn handle_delete_batch_query(
@@ -260,6 +249,53 @@ async fn handle_delete_batch_query(
 	})
 }
 
+pub(crate) async fn handle_poll_range(
+	garage: Arc<Garage>,
+	bucket_id: Uuid,
+	partition_key: &str,
+	req: Request<Body>,
+) -> Result<Response<Body>, Error> {
+	use garage_model::k2v::sub::PollRange;
+
+	let query = parse_json_body::<PollRangeQuery>(req).await?;
+
+	let timeout_msec = query.timeout.unwrap_or(300).clamp(1, 600) * 1000;
+
+	let resp = garage
+		.k2v
+		.rpc
+		.poll_range(
+			PollRange {
+				partition: K2VItemPartition {
+					bucket_id,
+					partition_key: partition_key.to_string(),
+				},
+				start: query.start,
+				end: query.end,
+				prefix: query.prefix,
+			},
+			query.seen_marker,
+			timeout_msec,
+		)
+		.await?;
+
+	if let Some((items, seen_marker)) = resp {
+		let resp = PollRangeResponse {
+			items: items
+				.into_iter()
+				.map(|(_k, i)| ReadBatchResponseItem::from(i))
+				.collect::<Vec<_>>(),
+			seen_marker,
+		};
+
+		Ok(json_ok_response(&resp)?)
+	} else {
+		Ok(Response::builder()
+			.status(StatusCode::NOT_MODIFIED)
+			.body(Body::empty())?)
+	}
+}
+
 #[derive(Deserialize)]
 struct InsertBatchItem {
 	pk: String,
@@ -364,3 +400,24 @@ struct DeleteBatchResponse {
 	#[serde(rename = "deletedItems")]
 	deleted_items: usize,
 }
+
+#[derive(Deserialize)]
+struct PollRangeQuery {
+	#[serde(default)]
+	prefix: Option<String>,
+	#[serde(default)]
+	start: Option<String>,
+	#[serde(default)]
+	end: Option<String>,
+	#[serde(default)]
+	timeout: Option<u64>,
+	#[serde(default, rename = "seenMarker")]
+	seen_marker: Option<String>,
+}
+
+#[derive(Serialize)]
+struct PollRangeResponse {
+	items: Vec<ReadBatchResponseItem>,
+	#[serde(rename = "seenMarker")]
+	seen_marker: String,
+}
diff --git a/src/api/k2v/index.rs b/src/api/k2v/index.rs
index 210950bf..6c1d4a91 100644
--- a/src/api/k2v/index.rs
+++ b/src/api/k2v/index.rs
@@ -1,10 +1,9 @@
 use std::sync::Arc;
 
-use hyper::{Body, Response, StatusCode};
+use hyper::{Body, Response};
 use serde::Serialize;
 
 use garage_util::data::*;
-use garage_util::error::Error as GarageError;
 
 use garage_rpc::ring::Ring;
 use garage_table::util::*;
@@ -12,6 +11,7 @@ use garage_table::util::*;
 use garage_model::garage::Garage;
 use garage_model::k2v::item_table::{BYTES, CONFLICTS, ENTRIES, VALUES};
 
+use crate::helpers::*;
 use crate::k2v::error::*;
 use crate::k2v::range::read_range;
 
@@ -68,10 +68,7 @@ pub async fn handle_read_index(
 		next_start,
 	};
 
-	let resp_json = serde_json::to_string_pretty(&resp).map_err(GarageError::from)?;
-	Ok(Response::builder()
-		.status(StatusCode::OK)
-		.body(Body::from(resp_json))?)
+	Ok(json_ok_response(&resp)?)
 }
 
 #[derive(Serialize)]
diff --git a/src/api/k2v/item.rs b/src/api/k2v/item.rs
index 041382c0..e13a0f30 100644
--- a/src/api/k2v/item.rs
+++ b/src/api/k2v/item.rs
@@ -134,9 +134,8 @@ pub async fn handle_insert_item(
 		.get(X_GARAGE_CAUSALITY_TOKEN)
 		.map(|s| s.to_str())
 		.transpose()?
-		.map(CausalContext::parse)
-		.transpose()
-		.ok_or_bad_request("Invalid causality token")?;
+		.map(CausalContext::parse_helper)
+		.transpose()?;
 
 	let body = hyper::body::to_bytes(req.into_body()).await?;
 	let value = DvvsValue::Value(body.to_vec());
@@ -170,9 +169,8 @@ pub async fn handle_delete_item(
 		.get(X_GARAGE_CAUSALITY_TOKEN)
 		.map(|s| s.to_str())
 		.transpose()?
-		.map(CausalContext::parse)
-		.transpose()
-		.ok_or_bad_request("Invalid causality token")?;
+		.map(CausalContext::parse_helper)
+		.transpose()?;
 
 	let value = DvvsValue::Deleted;
 
@@ -209,15 +207,17 @@ pub async fn handle_poll_item(
 	let causal_context =
 		CausalContext::parse(&causality_token).ok_or_bad_request("Invalid causality token")?;
 
+	let timeout_msec = timeout_secs.unwrap_or(300).clamp(1, 600) * 1000;
+
 	let item = garage
 		.k2v
 		.rpc
-		.poll(
+		.poll_item(
 			bucket_id,
 			partition_key,
 			sort_key,
 			causal_context,
-			timeout_secs.unwrap_or(300) * 1000,
+			timeout_msec,
 		)
 		.await?;
 
diff --git a/src/api/k2v/router.rs b/src/api/k2v/router.rs
index e7a3dd69..1cc58be5 100644
--- a/src/api/k2v/router.rs
+++ b/src/api/k2v/router.rs
@@ -32,6 +32,9 @@ pub enum Endpoint {
 		causality_token: String,
 		timeout: Option<u64>,
 	},
+	PollRange {
+		partition_key: String,
+	},
 	ReadBatch {
 	},
 	ReadIndex {
@@ -113,6 +116,7 @@ impl Endpoint {
 			@gen_parser
 			(query.keyword.take().unwrap_or_default(), partition_key, query, None),
 			key: [
+				POLL_RANGE => PollRange,
 			],
 			no_key: [
 				EMPTY => ReadBatch,
@@ -142,6 +146,7 @@ impl Endpoint {
 			@gen_parser
 			(query.keyword.take().unwrap_or_default(), partition_key, query, None),
 			key: [
+				POLL_RANGE => PollRange,
 			],
 			no_key: [
 				EMPTY => InsertBatch,
@@ -234,7 +239,8 @@ impl Endpoint {
 generateQueryParameters! {
 	keywords: [
 		"delete" => DELETE,
-		"search" => SEARCH
+		"search" => SEARCH,
+		"poll_range" => POLL_RANGE
 	],
 	fields: [
 		"prefix" => prefix,
diff --git a/src/garage/admin.rs b/src/garage/admin.rs
index 4eabebca..2ef3077c 100644
--- a/src/garage/admin.rs
+++ b/src/garage/admin.rs
@@ -911,7 +911,9 @@ impl AdminRpcHandler {
 			let role = layout.roles.get(id).and_then(|x| x.0.as_ref());
 			let hostname = status.map(|x| x.hostname.as_str()).unwrap_or("?");
 			let zone = role.map(|x| x.zone.as_str()).unwrap_or("?");
-			let capacity = role.map(|x| x.capacity_string()).unwrap_or("?".into());
+			let capacity = role
+				.map(|x| x.capacity_string())
+				.unwrap_or_else(|| "?".into());
 			let avail_str = |x| match x {
 				Some((avail, total)) => {
 					let pct = (avail as f64) / (total as f64) * 100.;
diff --git a/src/garage/tests/k2v/poll.rs b/src/garage/tests/k2v/poll.rs
index e56705ae..f54cc5d4 100644
--- a/src/garage/tests/k2v/poll.rs
+++ b/src/garage/tests/k2v/poll.rs
@@ -1,12 +1,16 @@
 use hyper::{Method, StatusCode};
 use std::time::Duration;
 
+use assert_json_diff::assert_json_eq;
+use serde_json::json;
+
+use super::json_body;
 use crate::common;
 
 #[tokio::test]
-async fn test_poll() {
+async fn test_poll_item() {
 	let ctx = common::context();
-	let bucket = ctx.create_bucket("test-k2v-poll");
+	let bucket = ctx.create_bucket("test-k2v-poll-item");
 
 	// Write initial value
 	let res = ctx
@@ -96,3 +100,165 @@ async fn test_poll() {
 		.to_vec();
 	assert_eq!(poll_res_body, b"New value");
 }
+
+#[tokio::test]
+async fn test_poll_range() {
+	let ctx = common::context();
+	let bucket = ctx.create_bucket("test-k2v-poll-range");
+
+	// Write initial value
+	let res = ctx
+		.k2v
+		.request
+		.builder(bucket.clone())
+		.method(Method::PUT)
+		.path("root")
+		.query_param("sort_key", Some("test1"))
+		.body(b"Initial value".to_vec())
+		.send()
+		.await
+		.unwrap();
+	assert_eq!(res.status(), StatusCode::NO_CONTENT);
+
+	// Retrieve initial value to get its causality token
+	let res2 = ctx
+		.k2v
+		.request
+		.builder(bucket.clone())
+		.path("root")
+		.query_param("sort_key", Some("test1"))
+		.signed_header("accept", "application/octet-stream")
+		.send()
+		.await
+		.unwrap();
+	assert_eq!(res2.status(), StatusCode::OK);
+	let ct = res2
+		.headers()
+		.get("x-garage-causality-token")
+		.unwrap()
+		.to_str()
+		.unwrap()
+		.to_string();
+
+	// Initial poll range, retrieve single item and first seen_marker
+	let res2 = ctx
+		.k2v
+		.request
+		.builder(bucket.clone())
+		.method(Method::POST)
+		.path("root")
+		.query_param("poll_range", None::<String>)
+		.body(b"{}".to_vec())
+		.send()
+		.await
+		.unwrap();
+	assert_eq!(res2.status(), StatusCode::OK);
+	let json_res = json_body(res2).await;
+	let seen_marker = json_res["seenMarker"].as_str().unwrap().to_string();
+	assert_json_eq!(
+		json_res,
+		json!(
+			{
+				"items": [
+				  {"sk": "test1", "ct": ct, "v": [base64::encode(b"Initial value")]},
+				],
+				"seenMarker": seen_marker,
+			}
+		)
+	);
+
+	// Second poll range, which will complete later
+	let poll = {
+		let bucket = bucket.clone();
+		tokio::spawn(async move {
+			let ctx = common::context();
+			ctx.k2v
+				.request
+				.builder(bucket.clone())
+				.method(Method::POST)
+				.path("root")
+				.query_param("poll_range", None::<String>)
+				.body(format!(r#"{{"seenMarker": "{}"}}"#, seen_marker).into_bytes())
+				.send()
+				.await
+		})
+	};
+
+	// Write new value that supersedes initial one
+	let res = ctx
+		.k2v
+		.request
+		.builder(bucket.clone())
+		.method(Method::PUT)
+		.path("root")
+		.query_param("sort_key", Some("test1"))
+		.signed_header("x-garage-causality-token", ct)
+		.body(b"New value".to_vec())
+		.send()
+		.await
+		.unwrap();
+	assert_eq!(res.status(), StatusCode::NO_CONTENT);
+
+	// Check poll finishes with correct value
+	let poll_res = tokio::select! {
+		_ = tokio::time::sleep(Duration::from_secs(10)) => panic!("poll did not terminate in time"),
+		res = poll => res.unwrap().unwrap(),
+	};
+
+	assert_eq!(poll_res.status(), StatusCode::OK);
+	let json_res = json_body(poll_res).await;
+	let seen_marker = json_res["seenMarker"].as_str().unwrap().to_string();
+	assert_eq!(json_res["items"].as_array().unwrap().len(), 1);
+	assert_json_eq!(&json_res["items"][0]["sk"], json!("test1"));
+	assert_json_eq!(
+		&json_res["items"][0]["v"],
+		json!([base64::encode(b"New value")])
+	);
+
+	// Now we will add a value on a different key
+	// Start a new poll operation
+	let poll = {
+		let bucket = bucket.clone();
+		tokio::spawn(async move {
+			let ctx = common::context();
+			ctx.k2v
+				.request
+				.builder(bucket.clone())
+				.method(Method::POST)
+				.path("root")
+				.query_param("poll_range", None::<String>)
+				.body(format!(r#"{{"seenMarker": "{}"}}"#, seen_marker).into_bytes())
+				.send()
+				.await
+		})
+	};
+
+	// Write value on different key
+	let res = ctx
+		.k2v
+		.request
+		.builder(bucket.clone())
+		.method(Method::PUT)
+		.path("root")
+		.query_param("sort_key", Some("test2"))
+		.body(b"Other value".to_vec())
+		.send()
+		.await
+		.unwrap();
+	assert_eq!(res.status(), StatusCode::NO_CONTENT);
+
+	// Check poll finishes with correct value
+	let poll_res = tokio::select! {
+		_ = tokio::time::sleep(Duration::from_secs(10)) => panic!("poll did not terminate in time"),
+		res = poll => res.unwrap().unwrap(),
+	};
+
+	assert_eq!(poll_res.status(), StatusCode::OK);
+	let json_res = json_body(poll_res).await;
+	assert_eq!(json_res["items"].as_array().unwrap().len(), 1);
+	assert_json_eq!(&json_res["items"][0]["sk"], json!("test2"));
+	assert_json_eq!(
+		&json_res["items"][0]["v"],
+		json!([base64::encode(b"Other value")])
+	);
+}
diff --git a/src/k2v-client/Cargo.toml b/src/k2v-client/Cargo.toml
index 7de2a55d..88d52747 100644
--- a/src/k2v-client/Cargo.toml
+++ b/src/k2v-client/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "k2v-client"
-version = "0.0.1"
+version = "0.1.1"
 authors = ["Trinity Pointard <trinity.pointard@gmail.com>", "Alex Auvolat <alex@adnab.me>"]
 edition = "2018"
 license = "AGPL-3.0"
@@ -15,6 +15,7 @@ log = "0.4"
 rusoto_core = { version = "0.48.0", default-features = false, features = ["rustls"] }
 rusoto_credential = "0.48.0"
 rusoto_signature = "0.48.0"
+hyper-rustls = { version = "0.23", default-features = false, features = [ "http1", "http2", "tls12" ] }
 serde = "1.0"
 serde_json = "1.0"
 thiserror = "1.0"
diff --git a/src/k2v-client/bin/k2v-cli.rs b/src/k2v-client/bin/k2v-cli.rs
index 925ebeb8..cdd63cce 100644
--- a/src/k2v-client/bin/k2v-cli.rs
+++ b/src/k2v-client/bin/k2v-cli.rs
@@ -1,3 +1,5 @@
+use std::collections::BTreeMap;
+use std::process::exit;
 use std::time::Duration;
 
 use k2v_client::*;
@@ -57,22 +59,39 @@ enum Command {
 		#[clap(flatten)]
 		output_kind: ReadOutputKind,
 	},
-	/// Watch changes on  a single value
-	Poll {
-		/// Partition key to delete from
+	/// Watch changes on a single value
+	PollItem {
+		/// Partition key of item to watch
 		partition_key: String,
-		/// Sort key to delete from
+		/// Sort key of item to watch
 		sort_key: String,
 		/// Causality information
 		#[clap(short, long)]
 		causality: String,
 		/// Timeout, in seconds
-		#[clap(short, long)]
+		#[clap(short = 'T', long)]
 		timeout: Option<u64>,
 		/// Output formating
 		#[clap(flatten)]
 		output_kind: ReadOutputKind,
 	},
+	/// Watch changes on a range of values
+	PollRange {
+		/// Partition key to poll from
+		partition_key: String,
+		/// Output only sort keys matching this filter
+		#[clap(flatten)]
+		filter: Filter,
+		/// Marker of data that had previously been seen by a PollRange
+		#[clap(short = 'S', long)]
+		seen_marker: Option<String>,
+		/// Timeout, in seconds
+		#[clap(short = 'T', long)]
+		timeout: Option<u64>,
+		/// Output formating
+		#[clap(flatten)]
+		output_kind: BatchOutputKind,
+	},
 	/// Delete a single value
 	Delete {
 		/// Partition key to delete from
@@ -176,7 +195,6 @@ struct ReadOutputKind {
 impl ReadOutputKind {
 	fn display_output(&self, val: CausalValue) -> ! {
 		use std::io::Write;
-		use std::process::exit;
 
 		if self.json {
 			let stdout = std::io::stdout();
@@ -254,6 +272,83 @@ struct BatchOutputKind {
 	json: bool,
 }
 
+impl BatchOutputKind {
+	fn display_human_output(&self, values: BTreeMap<String, CausalValue>) -> ! {
+		for (key, values) in values {
+			println!("key: {}", key);
+			let causality: String = values.causality.into();
+			println!("causality: {}", causality);
+			for value in values.value {
+				match value {
+					K2vValue::Value(v) => {
+						if let Ok(string) = std::str::from_utf8(&v) {
+							println!("  value(utf-8): {}", string);
+						} else {
+							println!("  value(base64): {}", base64::encode(&v));
+						}
+					}
+					K2vValue::Tombstone => {
+						println!("  tombstone");
+					}
+				}
+			}
+		}
+		exit(0);
+	}
+
+	fn values_json(&self, values: BTreeMap<String, CausalValue>) -> Vec<serde_json::Value> {
+		values
+			.into_iter()
+			.map(|(k, v)| {
+				let mut value = serde_json::to_value(v).unwrap();
+				value
+					.as_object_mut()
+					.unwrap()
+					.insert("sort_key".to_owned(), k.into());
+				value
+			})
+			.collect::<Vec<_>>()
+	}
+
+	fn display_poll_range_output(
+		&self,
+		seen_marker: String,
+		values: BTreeMap<String, CausalValue>,
+	) -> ! {
+		if self.json {
+			let json = serde_json::json!({
+				"values": self.values_json(values),
+				"seen_marker": seen_marker,
+			});
+
+			let stdout = std::io::stdout();
+			serde_json::to_writer_pretty(stdout, &json).unwrap();
+			exit(0)
+		} else {
+			println!("seen marker: {}", seen_marker);
+			self.display_human_output(values)
+		}
+	}
+
+	fn display_read_range_output(&self, res: PaginatedRange<CausalValue>) -> ! {
+		if self.json {
+			let json = serde_json::json!({
+				"next_key": res.next_start,
+				"values": self.values_json(res.items),
+			});
+
+			let stdout = std::io::stdout();
+			serde_json::to_writer_pretty(stdout, &json).unwrap();
+			exit(0)
+		} else {
+			if let Some(next) = res.next_start {
+				println!("next key: {}", next);
+			}
+			self.display_human_output(res.items)
+		}
+	}
+}
+
 /// Filter for batch operations
 #[derive(Parser, Debug)]
 #[clap(group = clap::ArgGroup::new("filter").multiple(true).required(true))]
@@ -342,7 +437,7 @@ async fn main() -> Result<(), Error> {
 			let res = client.read_item(&partition_key, &sort_key).await?;
 			output_kind.display_output(res);
 		}
-		Command::Poll {
+		Command::PollItem {
 			partition_key,
 			sort_key,
 			causality,
@@ -356,7 +451,54 @@ async fn main() -> Result<(), Error> {
 			if let Some(res) = res_opt {
 				output_kind.display_output(res);
 			} else {
-				println!("Delay expired and value didn't change.");
+				if output_kind.json {
+					println!("null");
+				} else {
+					println!("Delay expired and value didn't change.");
+				}
+			}
+		}
+		Command::PollRange {
+			partition_key,
+			filter,
+			seen_marker,
+			timeout,
+			output_kind,
+		} => {
+			if filter.conflicts_only
+				|| filter.tombstones
+				|| filter.reverse
+				|| filter.limit.is_some()
+			{
+				return Err(Error::Message(
+					"limit, reverse, conlicts-only, tombstones are invalid for poll-range".into(),
+				));
+			}
+
+			let timeout = timeout.map(Duration::from_secs);
+			let res = client
+				.poll_range(
+					&partition_key,
+					Some(PollRangeFilter {
+						start: filter.start.as_deref(),
+						end: filter.end.as_deref(),
+						prefix: filter.prefix.as_deref(),
+					}),
+					seen_marker.as_deref(),
+					timeout,
+				)
+				.await?;
+			match res {
+				Some((items, seen_marker)) => {
+					output_kind.display_poll_range_output(seen_marker, items);
+				}
+				None => {
+					if output_kind.json {
+						println!("null");
+					} else {
+						println!("Delay expired and value didn't change.");
+					}
+				}
 			}
 		}
 		Command::ReadIndex {
@@ -419,50 +561,7 @@ async fn main() -> Result<(), Error> {
 			};
 			let mut res = client.read_batch(&[op]).await?;
 			let res = res.pop().unwrap();
-			if output_kind.json {
-				let values = res
-					.items
-					.into_iter()
-					.map(|(k, v)| {
-						let mut value = serde_json::to_value(v).unwrap();
-						value
-							.as_object_mut()
-							.unwrap()
-							.insert("sort_key".to_owned(), k.into());
-						value
-					})
-					.collect::<Vec<_>>();
-				let json = serde_json::json!({
-					"next_key": res.next_start,
-					"values": values,
-				});
-
-				let stdout = std::io::stdout();
-				serde_json::to_writer_pretty(stdout, &json).unwrap();
-			} else {
-				if let Some(next) = res.next_start {
-					println!("next key: {}", next);
-				}
-				for (key, values) in res.items {
-					println!("key: {}", key);
-					let causality: String = values.causality.into();
-					println!("causality: {}", causality);
-					for value in values.value {
-						match value {
-							K2vValue::Value(v) => {
-								if let Ok(string) = std::str::from_utf8(&v) {
-									println!("  value(utf-8): {}", string);
-								} else {
-									println!("  value(base64): {}", base64::encode(&v));
-								}
-							}
-							K2vValue::Tombstone => {
-								println!("  tombstone");
-							}
-						}
-					}
-				}
-			}
+			output_kind.display_read_range_output(res);
 		}
 		Command::DeleteRange {
 			partition_key,
diff --git a/src/k2v-client/lib.rs b/src/k2v-client/lib.rs
index c2606af4..ca52d0cf 100644
--- a/src/k2v-client/lib.rs
+++ b/src/k2v-client/lib.rs
@@ -40,7 +40,13 @@ impl K2vClient {
 		creds: AwsCredentials,
 		user_agent: Option<String>,
 	) -> Result<Self, Error> {
-		let mut client = HttpClient::new()?;
+		let connector = hyper_rustls::HttpsConnectorBuilder::new()
+			.with_native_roots()
+			.https_or_http()
+			.enable_http1()
+			.enable_http2()
+			.build();
+		let mut client = HttpClient::from_connector(connector);
 		if let Some(ua) = user_agent {
 			client.local_agent_prepend(ua);
 		} else {
@@ -153,6 +159,58 @@ impl K2vClient {
 		}
 	}
 
+	/// Perform a PollRange request, waiting for any change in a given range of keys
+	/// to occur
+	pub async fn poll_range(
+		&self,
+		partition_key: &str,
+		filter: Option<PollRangeFilter<'_>>,
+		seen_marker: Option<&str>,
+		timeout: Option<Duration>,
+	) -> Result<Option<(BTreeMap<String, CausalValue>, String)>, Error> {
+		let timeout = timeout.unwrap_or(DEFAULT_POLL_TIMEOUT);
+
+		let request = PollRangeRequest {
+			filter: filter.unwrap_or_default(),
+			seen_marker,
+			timeout: timeout.as_secs(),
+		};
+
+		let mut req = SignedRequest::new(
+			"POST",
+			SERVICE,
+			&self.region,
+			&format!("/{}/{}", self.bucket, partition_key),
+		);
+		req.add_param("poll_range", "");
+
+		let payload = serde_json::to_vec(&request)?;
+		req.set_payload(Some(payload));
+		let res = self.dispatch(req, Some(timeout + DEFAULT_TIMEOUT)).await?;
+
+		if res.status == StatusCode::NOT_MODIFIED {
+			return Ok(None);
+		}
+
+		let resp: PollRangeResponse = serde_json::from_slice(&res.body)?;
+
+		let items = resp
+			.items
+			.into_iter()
+			.map(|BatchReadItem { sk, ct, v }| {
+				(
+					sk,
+					CausalValue {
+						causality: ct,
+						value: v,
+					},
+				)
+			})
+			.collect::<BTreeMap<_, _>>();
+
+		Ok(Some((items, resp.seen_marker)))
+	}
+
 	/// Perform an InsertItem request, inserting a value for a single pk+sk.
 	pub async fn insert_item(
 		&self,
@@ -389,6 +447,12 @@ impl From<CausalityToken> for String {
 	}
 }
 
+impl AsRef<str> for CausalityToken {
+	fn as_ref(&self) -> &str {
+		&self.0
+	}
+}
+
 /// A value in K2V. can be either a binary value, or a tombstone.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum K2vValue {
@@ -466,6 +530,29 @@ pub struct Filter<'a> {
 	pub reverse: bool,
 }
 
+#[derive(Debug, Default, Clone, Serialize)]
+pub struct PollRangeFilter<'a> {
+	pub start: Option<&'a str>,
+	pub end: Option<&'a str>,
+	pub prefix: Option<&'a str>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct PollRangeRequest<'a> {
+	#[serde(flatten)]
+	filter: PollRangeFilter<'a>,
+	seen_marker: Option<&'a str>,
+	timeout: u64,
+}
+
+#[derive(Debug, Clone, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct PollRangeResponse {
+	items: Vec<BatchReadItem>,
+	seen_marker: String,
+}
+
 impl<'a> Filter<'a> {
 	fn insert_params(&self, req: &mut SignedRequest) {
 		if let Some(start) = &self.start {
diff --git a/src/model/garage.rs b/src/model/garage.rs
index ffa54dc5..4716954a 100644
--- a/src/model/garage.rs
+++ b/src/model/garage.rs
@@ -27,7 +27,7 @@ use crate::index_counter::*;
 use crate::key_table::*;
 
 #[cfg(feature = "k2v")]
-use crate::k2v::{item_table::*, poll::*, rpc::*};
+use crate::k2v::{item_table::*, rpc::*, sub::*};
 
 /// An entire Garage full of data
 pub struct Garage {
@@ -305,8 +305,10 @@ impl GarageK2V {
 	fn new(system: Arc<System>, db: &db::Db, meta_rep_param: TableShardedReplication) -> Self {
 		info!("Initialize K2V counter table...");
 		let counter_table = IndexCounter::new(system.clone(), meta_rep_param.clone(), db);
+
 		info!("Initialize K2V subscription manager...");
 		let subscriptions = Arc::new(SubscriptionManager::new());
+
 		info!("Initialize K2V item table...");
 		let item_table = Table::new(
 			K2VItemTable {
@@ -317,7 +319,9 @@ impl GarageK2V {
 			system.clone(),
 			db,
 		);
-		let rpc = K2VRpcHandler::new(system, item_table.clone(), subscriptions);
+
+		info!("Initialize K2V RPC handler...");
+		let rpc = K2VRpcHandler::new(system, db, item_table.clone(), subscriptions);
 
 		Self {
 			item_table,
diff --git a/src/model/k2v/causality.rs b/src/model/k2v/causality.rs
index 62488d53..c80ebd39 100644
--- a/src/model/k2v/causality.rs
+++ b/src/model/k2v/causality.rs
@@ -1,3 +1,12 @@
+//! Implements a CausalContext, which is a set of timestamps for each
+//! node -- a vector clock --, indicating that the versions with
+//! timestamps <= these numbers have been seen and can be
+//! overwritten by a subsequent write.
+//!
+//! The textual representation of a CausalContext, which we call a
+//! "causality token", is used in the API and must be sent along with
+//! each write or delete operation to indicate the previously seen
+//! versions that we want to overwrite or delete.
 use base64::prelude::*;
 
 use std::collections::BTreeMap;
@@ -7,28 +16,44 @@ use serde::{Deserialize, Serialize};
 
 use garage_util::data::*;
 
+use crate::helper::error::{Error as HelperError, OkOrBadRequest};
+
 /// Node IDs used in K2V are u64 integers that are the abbreviation
 /// of full Garage node IDs which are 256-bit UUIDs.
 pub type K2VNodeId = u64;
 
+pub type VectorClock = BTreeMap<K2VNodeId, u64>;
+
 pub fn make_node_id(node_id: Uuid) -> K2VNodeId {
 	let mut tmp = [0u8; 8];
 	tmp.copy_from_slice(&node_id.as_slice()[..8]);
 	u64::from_be_bytes(tmp)
 }
 
-#[derive(PartialEq, Eq, Debug, Serialize, Deserialize)]
+pub fn vclock_gt(a: &VectorClock, b: &VectorClock) -> bool {
+	a.iter().any(|(n, ts)| ts > b.get(n).unwrap_or(&0))
+}
+
+pub fn vclock_max(a: &VectorClock, b: &VectorClock) -> VectorClock {
+	let mut ret = a.clone();
+	for (n, ts) in b.iter() {
+		let ent = ret.entry(*n).or_insert(0);
+		*ent = std::cmp::max(*ts, *ent);
+	}
+	ret
+}
+
+#[derive(PartialEq, Eq, Debug, Serialize, Deserialize, Default)]
 pub struct CausalContext {
-	pub vector_clock: BTreeMap<K2VNodeId, u64>,
+	pub vector_clock: VectorClock,
 }
 
 impl CausalContext {
 	/// Empty causality context
-	pub fn new_empty() -> Self {
-		Self {
-			vector_clock: BTreeMap::new(),
-		}
+	pub fn new() -> Self {
+		Self::default()
 	}
+
 	/// Make binary representation and encode in base64
 	pub fn serialize(&self) -> String {
 		let mut ints = Vec::with_capacity(2 * self.vector_clock.len());
@@ -45,13 +70,13 @@ impl CausalContext {
 
 		BASE64_URL_SAFE_NO_PAD.encode(bytes)
 	}
-	/// Parse from base64-encoded binary representation
-	pub fn parse(s: &str) -> Result<Self, String> {
-		let bytes = BASE64_URL_SAFE_NO_PAD
-			.decode(s)
-			.map_err(|e| format!("bad causality token base64: {}", e))?;
+
+	/// Parse from base64-encoded binary representation.
+	/// Returns None on error.
+	pub fn parse(s: &str) -> Option<Self> {
+		let bytes = BASE64_URL_SAFE_NO_PAD.decode(s).ok()?;
 		if bytes.len() % 16 != 8 || bytes.len() < 8 {
-			return Err("bad causality token length".into());
+			return None;
 		}
 
 		let checksum = u64::from_be_bytes(bytes[..8].try_into().unwrap());
@@ -68,16 +93,19 @@ impl CausalContext {
 		let check = ret.vector_clock.iter().fold(0, |acc, (n, t)| acc ^ *n ^ *t);
 
 		if check != checksum {
-			return Err("bad causality token checksum".into());
+			return None;
 		}
 
-		Ok(ret)
+		Some(ret)
 	}
+
+	pub fn parse_helper(s: &str) -> Result<Self, HelperError> {
+		Self::parse(s).ok_or_bad_request("Invalid causality token")
+	}
+
 	/// Check if this causal context contains newer items than another one
 	pub fn is_newer_than(&self, other: &Self) -> bool {
-		self.vector_clock
-			.iter()
-			.any(|(k, v)| v > other.vector_clock.get(k).unwrap_or(&0))
+		vclock_gt(&self.vector_clock, &other.vector_clock)
 	}
 }
 
diff --git a/src/model/k2v/item_table.rs b/src/model/k2v/item_table.rs
index 9955a9cd..28646f37 100644
--- a/src/model/k2v/item_table.rs
+++ b/src/model/k2v/item_table.rs
@@ -11,7 +11,7 @@ use garage_table::*;
 
 use crate::index_counter::*;
 use crate::k2v::causality::*;
-use crate::k2v::poll::*;
+use crate::k2v::sub::*;
 
 pub const ENTRIES: &str = "entries";
 pub const CONFLICTS: &str = "conflicts";
@@ -73,7 +73,8 @@ impl K2VItem {
 		this_node: Uuid,
 		context: &Option<CausalContext>,
 		new_value: DvvsValue,
-	) {
+		node_ts: u64,
+	) -> u64 {
 		if let Some(context) = context {
 			for (node, t_discard) in context.vector_clock.iter() {
 				if let Some(e) = self.items.get_mut(node) {
@@ -98,12 +99,14 @@ impl K2VItem {
 			values: vec![],
 		});
 		let t_prev = e.max_time();
-		e.values.push((t_prev + 1, new_value));
+		let t_new = std::cmp::max(t_prev + 1, node_ts + 1);
+		e.values.push((t_new, new_value));
+		t_new
 	}
 
 	/// Extract the causality context of a K2V Item
 	pub fn causal_context(&self) -> CausalContext {
-		let mut cc = CausalContext::new_empty();
+		let mut cc = CausalContext::new();
 		for (node, ent) in self.items.iter() {
 			cc.vector_clock.insert(*node, ent.max_time());
 		}
diff --git a/src/model/k2v/mod.rs b/src/model/k2v/mod.rs
index f6a96151..acc1fcdc 100644
--- a/src/model/k2v/mod.rs
+++ b/src/model/k2v/mod.rs
@@ -1,6 +1,8 @@
 pub mod causality;
+pub mod seen;
 
 pub mod item_table;
 
-pub mod poll;
 pub mod rpc;
+
+pub mod sub;
diff --git a/src/model/k2v/poll.rs b/src/model/k2v/poll.rs
deleted file mode 100644
index 93105207..00000000
--- a/src/model/k2v/poll.rs
+++ /dev/null
@@ -1,50 +0,0 @@
-use std::collections::HashMap;
-use std::sync::Mutex;
-
-use serde::{Deserialize, Serialize};
-use tokio::sync::broadcast;
-
-use crate::k2v::item_table::*;
-
-#[derive(Debug, Hash, Clone, PartialEq, Eq, Serialize, Deserialize)]
-pub struct PollKey {
-	pub partition: K2VItemPartition,
-	pub sort_key: String,
-}
-
-#[derive(Default)]
-pub struct SubscriptionManager {
-	subscriptions: Mutex<HashMap<PollKey, broadcast::Sender<K2VItem>>>,
-}
-
-impl SubscriptionManager {
-	pub fn new() -> Self {
-		Self::default()
-	}
-
-	pub fn subscribe(&self, key: &PollKey) -> broadcast::Receiver<K2VItem> {
-		let mut subs = self.subscriptions.lock().unwrap();
-		if let Some(s) = subs.get(key) {
-			s.subscribe()
-		} else {
-			let (tx, rx) = broadcast::channel(8);
-			subs.insert(key.clone(), tx);
-			rx
-		}
-	}
-
-	pub fn notify(&self, item: &K2VItem) {
-		let key = PollKey {
-			partition: item.partition.clone(),
-			sort_key: item.sort_key.clone(),
-		};
-		let mut subs = self.subscriptions.lock().unwrap();
-		if let Some(s) = subs.get(&key) {
-			if s.send(item.clone()).is_err() {
-				// no more subscribers, remove channel from here
-				// (we will re-create it later if we need to subscribe again)
-				subs.remove(&key);
-			}
-		}
-	}
-}
diff --git a/src/model/k2v/rpc.rs b/src/model/k2v/rpc.rs
index f64a7984..117103b6 100644
--- a/src/model/k2v/rpc.rs
+++ b/src/model/k2v/rpc.rs
@@ -5,9 +5,10 @@
 //! node does not process the entry directly, as this would
 //! mean the vector clock gets much larger than needed).
 
-use std::collections::HashMap;
-use std::sync::Arc;
-use std::time::Duration;
+use std::collections::{BTreeMap, HashMap};
+use std::convert::TryInto;
+use std::sync::{Arc, Mutex, MutexGuard};
+use std::time::{Duration, Instant};
 
 use async_trait::async_trait;
 use futures::stream::FuturesUnordered;
@@ -15,9 +16,12 @@ use futures::StreamExt;
 use serde::{Deserialize, Serialize};
 use tokio::select;
 
+use garage_db as db;
+
 use garage_util::crdt::*;
 use garage_util::data::*;
 use garage_util::error::*;
+use garage_util::time::now_msec;
 
 use garage_rpc::system::System;
 use garage_rpc::*;
@@ -25,9 +29,15 @@ use garage_rpc::*;
 use garage_table::replication::{TableReplication, TableShardedReplication};
 use garage_table::{PartitionKey, Table};
 
+use crate::helper::error::Error as HelperError;
 use crate::k2v::causality::*;
 use crate::k2v::item_table::*;
-use crate::k2v::poll::*;
+use crate::k2v::seen::*;
+use crate::k2v::sub::*;
+
+const POLL_RANGE_EXTRA_DELAY: Duration = Duration::from_millis(200);
+
+const TIMESTAMP_KEY: &'static [u8] = b"timestamp";
 
 /// RPC messages for K2V
 #[derive(Debug, Serialize, Deserialize)]
@@ -40,7 +50,13 @@ enum K2VRpc {
 		causal_context: CausalContext,
 		timeout_msec: u64,
 	},
+	PollRange {
+		range: PollRange,
+		seen_str: Option<String>,
+		timeout_msec: u64,
+	},
 	PollItemResponse(Option<K2VItem>),
+	PollRangeResponse(Uuid, Vec<K2VItem>),
 }
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -59,6 +75,12 @@ impl Rpc for K2VRpc {
 pub struct K2VRpcHandler {
 	system: Arc<System>,
 	item_table: Arc<Table<K2VItemTable, TableShardedReplication>>,
+
+	// Using a mutex on the local_timestamp_tree is not strictly necessary,
+	// but it helps to not try to do several inserts at the same time,
+	// which would create transaction conflicts and force many useless retries.
+	local_timestamp_tree: Mutex<db::Tree>,
+
 	endpoint: Arc<Endpoint<K2VRpc, Self>>,
 	subscriptions: Arc<SubscriptionManager>,
 }
@@ -66,14 +88,19 @@ pub struct K2VRpcHandler {
 impl K2VRpcHandler {
 	pub fn new(
 		system: Arc<System>,
+		db: &db::Db,
 		item_table: Arc<Table<K2VItemTable, TableShardedReplication>>,
 		subscriptions: Arc<SubscriptionManager>,
 	) -> Arc<Self> {
+		let local_timestamp_tree = db
+			.open_tree("k2v_local_timestamp")
+			.expect("Unable to open DB tree for k2v local timestamp");
 		let endpoint = system.netapp.endpoint("garage_model/k2v/Rpc".to_string());
 
 		let rpc_handler = Arc::new(Self {
 			system,
 			item_table,
+			local_timestamp_tree: Mutex::new(local_timestamp_tree),
 			endpoint,
 			subscriptions,
 		});
@@ -181,7 +208,7 @@ impl K2VRpcHandler {
 		Ok(())
 	}
 
-	pub async fn poll(
+	pub async fn poll_item(
 		&self,
 		bucket_id: Uuid,
 		partition_key: String,
@@ -230,9 +257,7 @@ impl K2VRpcHandler {
 						resp = Some(x);
 					}
 				}
-				K2VRpc::PollItemResponse(None) => {
-					return Ok(None);
-				}
+				K2VRpc::PollItemResponse(None) => (),
 				v => return Err(Error::unexpected_rpc_message(v)),
 			}
 		}
@@ -240,10 +265,117 @@ impl K2VRpcHandler {
 		Ok(resp)
 	}
 
+	pub async fn poll_range(
+		&self,
+		range: PollRange,
+		seen_str: Option<String>,
+		timeout_msec: u64,
+	) -> Result<Option<(BTreeMap<String, K2VItem>, String)>, HelperError> {
+		let has_seen_marker = seen_str.is_some();
+
+		// Parse seen marker, we will use it below. This is also the first check
+		// that it is valid, which returns a bad request error if not.
+		let mut seen = seen_str
+			.as_deref()
+			.map(RangeSeenMarker::decode_helper)
+			.transpose()?
+			.unwrap_or_default();
+		seen.restrict(&range);
+
+		// Prepare PollRange RPC to send to the storage nodes responsible for the parititon
+		let nodes = self
+			.item_table
+			.data
+			.replication
+			.write_nodes(&range.partition.hash());
+		let quorum = self.item_table.data.replication.read_quorum();
+		let msg = K2VRpc::PollRange {
+			range,
+			seen_str,
+			timeout_msec,
+		};
+
+		// Send the request to all nodes, use FuturesUnordered to get the responses in any order
+		let msg = msg.into_req().map_err(netapp::error::Error::from)?;
+		let rs = RequestStrategy::with_priority(PRIO_NORMAL).without_timeout();
+		let mut requests = nodes
+			.iter()
+			.map(|node| self.system.rpc.call(&self.endpoint, *node, msg.clone(), rs))
+			.collect::<FuturesUnordered<_>>();
+
+		// Fetch responses. This procedure stops fetching responses when any of the following
+		// conditions arise:
+		// - we have a response to all requests
+		// - we have a response to a read quorum of requests (e.g. 2/3), and an extra delay
+		//   has passed since the quorum was achieved
+		// - a global RPC timeout expired
+		// The extra delay after a quorum was received is usefull if the third response was to
+		// arrive during this short interval: this would allow us to consider all the data seen
+		// by that last node in the response we produce, and would likely help reduce the
+		// size of the seen marker that we will return (because we would have an info of the
+		// kind: all items produced by that node until time ts have been returned, so we can
+		// bump the entry in the global vector clock and possibly remove some item-specific
+		// vector clocks)
+		let mut deadline =
+			Instant::now() + Duration::from_millis(timeout_msec) + self.system.rpc.rpc_timeout();
+		let mut resps = vec![];
+		let mut errors = vec![];
+		loop {
+			select! {
+				_ =	tokio::time::sleep_until(deadline.into()) => {
+					break;
+				}
+				res = requests.next() => match res {
+					None => break,
+					Some(Err(e)) => errors.push(e),
+					Some(Ok(r)) => {
+						resps.push(r);
+						if resps.len() >= quorum {
+							deadline = std::cmp::min(deadline, Instant::now() + POLL_RANGE_EXTRA_DELAY);
+						}
+					}
+				}
+			}
+		}
+		if errors.len() > nodes.len() - quorum {
+			let errors = errors.iter().map(|e| format!("{}", e)).collect::<Vec<_>>();
+			return Err(Error::Quorum(quorum, resps.len(), nodes.len(), errors).into());
+		}
+
+		// Take all returned items into account to produce the response.
+		let mut new_items = BTreeMap::<String, K2VItem>::new();
+		for v in resps {
+			if let K2VRpc::PollRangeResponse(node, items) = v {
+				seen.mark_seen_node_items(node, items.iter());
+				for item in items.into_iter() {
+					match new_items.get_mut(&item.sort_key) {
+						Some(ent) => {
+							ent.merge(&item);
+						}
+						None => {
+							new_items.insert(item.sort_key.clone(), item);
+						}
+					}
+				}
+			} else {
+				return Err(Error::unexpected_rpc_message(v).into());
+			}
+		}
+
+		if new_items.is_empty() && has_seen_marker {
+			Ok(None)
+		} else {
+			Ok(Some((new_items, seen.encode()?)))
+		}
+	}
+
 	// ---- internal handlers ----
 
 	async fn handle_insert(&self, item: &InsertedItem) -> Result<K2VRpc, Error> {
-		let new = self.local_insert(item)?;
+		let new = {
+			let local_timestamp_tree = self.local_timestamp_tree.lock().unwrap();
+			self.local_insert(&local_timestamp_tree, item)?
+		};
 
 		// Propagate to rest of network
 		if let Some(updated) = new {
@@ -256,11 +388,14 @@ impl K2VRpcHandler {
 	async fn handle_insert_many(&self, items: &[InsertedItem]) -> Result<K2VRpc, Error> {
 		let mut updated_vec = vec![];
 
-		for item in items {
-			let new = self.local_insert(item)?;
+		{
+			let local_timestamp_tree = self.local_timestamp_tree.lock().unwrap();
+			for item in items {
+				let new = self.local_insert(&local_timestamp_tree, item)?;
 
-			if let Some(updated) = new {
-				updated_vec.push(updated);
+				if let Some(updated) = new {
+					updated_vec.push(updated);
+				}
 			}
 		}
 
@@ -272,10 +407,22 @@ impl K2VRpcHandler {
 		Ok(K2VRpc::Ok)
 	}
 
-	fn local_insert(&self, item: &InsertedItem) -> Result<Option<K2VItem>, Error> {
+	fn local_insert(
+		&self,
+		local_timestamp_tree: &MutexGuard<'_, db::Tree>,
+		item: &InsertedItem,
+	) -> Result<Option<K2VItem>, Error> {
+		let now = now_msec();
+
 		self.item_table
 			.data
-			.update_entry_with(&item.partition, &item.sort_key, |ent| {
+			.update_entry_with(&item.partition, &item.sort_key, |tx, ent| {
+				let old_local_timestamp = tx
+					.get(&local_timestamp_tree, TIMESTAMP_KEY)?
+					.and_then(|x| x.try_into().ok())
+					.map(u64::from_be_bytes)
+					.unwrap_or_default();
+
 				let mut ent = ent.unwrap_or_else(|| {
 					K2VItem::new(
 						item.partition.bucket_id,
@@ -283,13 +430,25 @@ impl K2VRpcHandler {
 						item.sort_key.clone(),
 					)
 				});
-				ent.update(self.system.id, &item.causal_context, item.value.clone());
-				ent
+				let new_local_timestamp = ent.update(
+					self.system.id,
+					&item.causal_context,
+					item.value.clone(),
+					std::cmp::max(old_local_timestamp, now),
+				);
+
+				tx.insert(
+					&local_timestamp_tree,
+					TIMESTAMP_KEY,
+					u64::to_be_bytes(new_local_timestamp),
+				)?;
+
+				Ok(ent)
 			})
 	}
 
-	async fn handle_poll(&self, key: &PollKey, ct: &CausalContext) -> Result<K2VItem, Error> {
-		let mut chan = self.subscriptions.subscribe(key);
+	async fn handle_poll_item(&self, key: &PollKey, ct: &CausalContext) -> Result<K2VItem, Error> {
+		let mut chan = self.subscriptions.subscribe_item(key);
 
 		let mut value = self
 			.item_table
@@ -311,6 +470,71 @@ impl K2VRpcHandler {
 
 		Ok(value)
 	}
+
+	async fn handle_poll_range(
+		&self,
+		range: &PollRange,
+		seen_str: &Option<String>,
+	) -> Result<Vec<K2VItem>, Error> {
+		if let Some(seen_str) = seen_str {
+			let seen = RangeSeenMarker::decode(seen_str).ok_or_message("Invalid seenMarker")?;
+
+			// Subscribe now to all changes on that partition,
+			// so that new items that are inserted while we are reading the range
+			// will be seen in the loop below
+			let mut chan = self.subscriptions.subscribe_partition(&range.partition);
+
+			// Check for the presence of any new items already stored in the item table
+			let mut new_items = self.poll_range_read_range(range, &seen)?;
+
+			// If we found no new items, wait for a matching item to arrive
+			// on the channel
+			while new_items.is_empty() {
+				let item = chan.recv().await?;
+				if range.matches(&item) && seen.is_new_item(&item) {
+					new_items.push(item);
+				}
+			}
+
+			Ok(new_items)
+		} else {
+			// If no seen marker was specified, we do not poll for anything.
+			// We return immediately with the set of known items (even if
+			// it is empty), which will give the client an inital view of
+			// the dataset and an initial seen marker for further
+			// PollRange calls.
+			self.poll_range_read_range(range, &RangeSeenMarker::default())
+		}
+	}
+
+	fn poll_range_read_range(
+		&self,
+		range: &PollRange,
+		seen: &RangeSeenMarker,
+	) -> Result<Vec<K2VItem>, Error> {
+		let mut new_items = vec![];
+
+		let partition_hash = range.partition.hash();
+		let first_key = match &range.start {
+			None => partition_hash.to_vec(),
+			Some(sk) => self.item_table.data.tree_key(&range.partition, sk),
+		};
+		for item in self.item_table.data.store.range(first_key..)? {
+			let (key, value) = item?;
+			if &key[..32] != partition_hash.as_slice() {
+				break;
+			}
+			let item = self.item_table.data.decode_entry(&value)?;
+			if !range.matches(&item) {
+				break;
+			}
+			if seen.is_new_item(&item) {
+				new_items.push(item);
+			}
+		}
+
+		Ok(new_items)
+	}
 }
 
 #[async_trait]
@@ -326,10 +550,21 @@ impl EndpointHandler<K2VRpc> for K2VRpcHandler {
 			} => {
 				let delay = tokio::time::sleep(Duration::from_millis(*timeout_msec));
 				select! {
-					ret = self.handle_poll(key, causal_context) => ret.map(Some).map(K2VRpc::PollItemResponse),
+					ret = self.handle_poll_item(key, causal_context) => ret.map(Some).map(K2VRpc::PollItemResponse),
 					_ = delay => Ok(K2VRpc::PollItemResponse(None)),
 				}
 			}
+			K2VRpc::PollRange {
+				range,
+				seen_str,
+				timeout_msec,
+			} => {
+				let delay = tokio::time::sleep(Duration::from_millis(*timeout_msec));
+				select! {
+					ret = self.handle_poll_range(range, seen_str) => ret.map(|items| K2VRpc::PollRangeResponse(self.system.id, items)),
+					_ = delay => Ok(K2VRpc::PollRangeResponse(self.system.id, vec![])),
+				}
+			}
 			m => Err(Error::unexpected_rpc_message(m)),
 		}
 	}
diff --git a/src/model/k2v/seen.rs b/src/model/k2v/seen.rs
new file mode 100644
index 00000000..51098710
--- /dev/null
+++ b/src/model/k2v/seen.rs
@@ -0,0 +1,105 @@
+//! Implements a RangeSeenMarker, a data type used in the PollRange API
+//! to indicate which items in the range have already been seen
+//! and which have not been seen yet.
+//!
+//! It consists of a vector clock that indicates that for each node,
+//! all items produced by that node with timestamps <= the value in the
+//! vector clock has been seen, as well as a set of causal contexts for
+//! individual items.
+
+use std::collections::BTreeMap;
+
+use base64::prelude::*;
+use serde::{Deserialize, Serialize};
+
+use garage_util::data::Uuid;
+use garage_util::encode::{nonversioned_decode, nonversioned_encode};
+use garage_util::error::Error;
+
+use crate::helper::error::{Error as HelperError, OkOrBadRequest};
+use crate::k2v::causality::*;
+use crate::k2v::item_table::*;
+use crate::k2v::sub::*;
+
+#[derive(Debug, Serialize, Deserialize, Default)]
+pub struct RangeSeenMarker {
+	vector_clock: VectorClock,
+	items: BTreeMap<String, VectorClock>,
+}
+
+impl RangeSeenMarker {
+	pub fn new() -> Self {
+		Self::default()
+	}
+
+	pub fn restrict(&mut self, range: &PollRange) {
+		if let Some(start) = &range.start {
+			self.items = self.items.split_off(start);
+		}
+		if let Some(end) = &range.end {
+			self.items.split_off(end);
+		}
+		if let Some(pfx) = &range.prefix {
+			self.items.retain(|k, _v| k.starts_with(pfx));
+		}
+	}
+
+	pub fn mark_seen_node_items<'a, I: IntoIterator<Item = &'a K2VItem>>(
+		&mut self,
+		node: Uuid,
+		items: I,
+	) {
+		let node = make_node_id(node);
+		for item in items.into_iter() {
+			let cc = item.causal_context();
+
+			if let Some(ts) = cc.vector_clock.get(&node) {
+				let ent = self.vector_clock.entry(node).or_insert(0);
+				*ent = std::cmp::max(*ent, *ts);
+			}
+
+			if vclock_gt(&cc.vector_clock, &self.vector_clock) {
+				match self.items.get_mut(&item.sort_key) {
+					None => {
+						self.items.insert(item.sort_key.clone(), cc.vector_clock);
+					}
+					Some(ent) => *ent = vclock_max(&ent, &cc.vector_clock),
+				}
+			}
+		}
+	}
+
+	pub fn canonicalize(&mut self) {
+		let self_vc = &self.vector_clock;
+		self.items.retain(|_sk, vc| vclock_gt(&vc, self_vc))
+	}
+
+	pub fn encode(&mut self) -> Result<String, Error> {
+		self.canonicalize();
+
+		let bytes = nonversioned_encode(&self)?;
+		let bytes = zstd::stream::encode_all(&mut &bytes[..], zstd::DEFAULT_COMPRESSION_LEVEL)?;
+		Ok(BASE64_STANDARD.encode(&bytes))
+	}
+
+	/// Decode from msgpack+zstd+b64 representation, returns None on error.
+	pub fn decode(s: &str) -> Option<Self> {
+		let bytes = BASE64_STANDARD.decode(&s).ok()?;
+		let bytes = zstd::stream::decode_all(&mut &bytes[..]).ok()?;
+		nonversioned_decode(&bytes).ok()
+	}
+
+	pub fn decode_helper(s: &str) -> Result<Self, HelperError> {
+		Self::decode(s).ok_or_bad_request("Invalid causality token")
+	}
+
+	pub fn is_new_item(&self, item: &K2VItem) -> bool {
+		let cc = item.causal_context();
+		vclock_gt(&cc.vector_clock, &self.vector_clock)
+			&& self
+				.items
+				.get(&item.sort_key)
+				.map(|vc| vclock_gt(&cc.vector_clock, &vc))
+				.unwrap_or(true)
+	}
+}
diff --git a/src/model/k2v/sub.rs b/src/model/k2v/sub.rs
new file mode 100644
index 00000000..b1daa271
--- /dev/null
+++ b/src/model/k2v/sub.rs
@@ -0,0 +1,110 @@
+use std::collections::HashMap;
+use std::sync::Mutex;
+
+use serde::{Deserialize, Serialize};
+use tokio::sync::broadcast;
+
+use crate::k2v::item_table::*;
+
+#[derive(Debug, Hash, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct PollKey {
+	pub partition: K2VItemPartition,
+	pub sort_key: String,
+}
+
+#[derive(Debug, Hash, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct PollRange {
+	pub partition: K2VItemPartition,
+	pub prefix: Option<String>,
+	pub start: Option<String>,
+	pub end: Option<String>,
+}
+
+#[derive(Default)]
+pub struct SubscriptionManager(Mutex<SubscriptionManagerInner>);
+
+#[derive(Default)]
+pub struct SubscriptionManagerInner {
+	item_subscriptions: HashMap<PollKey, broadcast::Sender<K2VItem>>,
+	part_subscriptions: HashMap<K2VItemPartition, broadcast::Sender<K2VItem>>,
+}
+
+impl SubscriptionManager {
+	pub fn new() -> Self {
+		Self::default()
+	}
+
+	pub(crate) fn subscribe_item(&self, key: &PollKey) -> broadcast::Receiver<K2VItem> {
+		let mut inner = self.0.lock().unwrap();
+		if let Some(s) = inner.item_subscriptions.get(key) {
+			s.subscribe()
+		} else {
+			let (tx, rx) = broadcast::channel(8);
+			inner.item_subscriptions.insert(key.clone(), tx);
+			rx
+		}
+	}
+
+	pub(crate) fn subscribe_partition(
+		&self,
+		part: &K2VItemPartition,
+	) -> broadcast::Receiver<K2VItem> {
+		let mut inner = self.0.lock().unwrap();
+		if let Some(s) = inner.part_subscriptions.get(part) {
+			s.subscribe()
+		} else {
+			let (tx, rx) = broadcast::channel(8);
+			inner.part_subscriptions.insert(part.clone(), tx);
+			rx
+		}
+	}
+
+	pub(crate) fn notify(&self, item: &K2VItem) {
+		let mut inner = self.0.lock().unwrap();
+
+		// 1. Notify single item subscribers,
+		// removing subscriptions with no more listeners if any
+		let key = PollKey {
+			partition: item.partition.clone(),
+			sort_key: item.sort_key.clone(),
+		};
+		if let Some(s) = inner.item_subscriptions.get(&key) {
+			if s.send(item.clone()).is_err() {
+				// no more subscribers, remove channel from here
+				// (we will re-create it later if we need to subscribe again)
+				inner.item_subscriptions.remove(&key);
+			}
+		}
+
+		// 2. Notify partition subscribers,
+		// removing subscriptions with no more listeners if any
+		if let Some(s) = inner.part_subscriptions.get(&item.partition) {
+			if s.send(item.clone()).is_err() {
+				// no more subscribers, remove channel from here
+				// (we will re-create it later if we need to subscribe again)
+				inner.part_subscriptions.remove(&item.partition);
+			}
+		}
+	}
+}
+
+impl PollRange {
+	pub fn matches(&self, item: &K2VItem) -> bool {
+		item.partition == self.partition
+			&& self
+				.prefix
+				.as_ref()
+				.map(|x| item.sort_key.starts_with(x))
+				.unwrap_or(true)
+			&& self
+				.start
+				.as_ref()
+				.map(|x| item.sort_key >= *x)
+				.unwrap_or(true)
+			&& self
+				.end
+				.as_ref()
+				.map(|x| item.sort_key < *x)
+				.unwrap_or(true)
+	}
+}
diff --git a/src/rpc/rpc_helper.rs b/src/rpc/rpc_helper.rs
index 1ec250c3..e59c372a 100644
--- a/src/rpc/rpc_helper.rs
+++ b/src/rpc/rpc_helper.rs
@@ -15,10 +15,9 @@ use opentelemetry::{
 };
 
 pub use netapp::endpoint::{Endpoint, EndpointHandler, StreamingEndpointHandler};
-use netapp::message::IntoReq;
 pub use netapp::message::{
-	Message as Rpc, OrderTag, Req, RequestPriority, Resp, PRIO_BACKGROUND, PRIO_HIGH, PRIO_NORMAL,
-	PRIO_SECONDARY,
+	IntoReq, Message as Rpc, OrderTag, Req, RequestPriority, Resp, PRIO_BACKGROUND, PRIO_HIGH,
+	PRIO_NORMAL, PRIO_SECONDARY,
 };
 use netapp::peering::fullmesh::FullMeshPeeringStrategy;
 pub use netapp::{self, NetApp, NodeID};
diff --git a/src/table/data.rs b/src/table/data.rs
index 5c792f1f..26cc3a5a 100644
--- a/src/table/data.rs
+++ b/src/table/data.rs
@@ -181,13 +181,17 @@ impl<F: TableSchema, R: TableReplication> TableData<F, R> {
 	pub(crate) fn update_entry(&self, update_bytes: &[u8]) -> Result<(), Error> {
 		let update = self.decode_entry(update_bytes)?;
 
-		self.update_entry_with(update.partition_key(), update.sort_key(), |ent| match ent {
-			Some(mut ent) => {
-				ent.merge(&update);
-				ent
-			}
-			None => update.clone(),
-		})?;
+		self.update_entry_with(
+			update.partition_key(),
+			update.sort_key(),
+			|_tx, ent| match ent {
+				Some(mut ent) => {
+					ent.merge(&update);
+					Ok(ent)
+				}
+				None => Ok(update.clone()),
+			},
+		)?;
 		Ok(())
 	}
 
@@ -195,7 +199,7 @@ impl<F: TableSchema, R: TableReplication> TableData<F, R> {
 		&self,
 		partition_key: &F::P,
 		sort_key: &F::S,
-		f: impl Fn(Option<F::E>) -> F::E,
+		update_fn: impl Fn(&mut db::Transaction, Option<F::E>) -> db::TxOpResult<F::E>,
 	) -> Result<Option<F::E>, Error> {
 		let tree_key = self.tree_key(partition_key, sort_key);
 
@@ -203,10 +207,10 @@ impl<F: TableSchema, R: TableReplication> TableData<F, R> {
 			let (old_entry, old_bytes, new_entry) = match tx.get(&self.store, &tree_key)? {
 				Some(old_bytes) => {
 					let old_entry = self.decode_entry(&old_bytes).map_err(db::TxError::Abort)?;
-					let new_entry = f(Some(old_entry.clone()));
+					let new_entry = update_fn(&mut tx, Some(old_entry.clone()))?;
 					(Some(old_entry), Some(old_bytes), new_entry)
 				}
-				None => (None, None, f(None)),
+				None => (None, None, update_fn(&mut tx, None)?),
 			};
 
 			// Changed can be true in two scenarios