1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
|
use std::convert::TryInto;
use garage_db as db;
use garage_util::data::*;
use garage_util::error::*;
use garage_util::time::*;
use crate::manager::BLOCK_GC_DELAY;
pub struct BlockRc {
pub(crate) rc: db::Tree,
}
impl BlockRc {
pub(crate) fn new(rc: db::Tree) -> Self {
Self { rc }
}
/// Increment the reference counter associated to a hash.
/// Returns true if the RC goes from zero to nonzero.
pub(crate) fn block_incref(&self, tx: &mut db::Transaction, hash: &Hash) -> db::Result<bool> {
let old_rc = RcEntry::parse_opt(tx.get(&self.rc, &hash)?);
match old_rc.increment().serialize() {
Some(x) => tx.insert(&self.rc, &hash, x)?,
None => unreachable!(),
};
Ok(old_rc.is_zero())
}
/// Decrement the reference counter associated to a hash.
/// Returns true if the RC is now zero.
pub(crate) fn block_decref(&self, tx: &mut db::Transaction, hash: &Hash) -> db::Result<bool> {
let new_rc = RcEntry::parse_opt(tx.get(&self.rc, &hash)?).decrement();
match new_rc.serialize() {
Some(x) => tx.insert(&self.rc, &hash, x)?,
None => tx.remove(&self.rc, &hash)?,
};
Ok(matches!(new_rc, RcEntry::Deletable { .. }))
}
/// Read a block's reference count
pub(crate) fn get_block_rc(&self, hash: &Hash) -> Result<RcEntry, Error> {
Ok(RcEntry::parse_opt(self.rc.get(hash.as_ref())?))
}
/// Delete an entry in the RC table if it is deletable and the
/// deletion time has passed
pub(crate) fn clear_deleted_block_rc(&self, hash: &Hash) -> Result<(), Error> {
let now = now_msec();
self.rc.db().transaction(|mut tx| {
let rcval = RcEntry::parse_opt(tx.get(&self.rc, &hash)?);
match rcval {
RcEntry::Deletable { at_time } if now > at_time => {
tx.remove(&self.rc, &hash)?;
}
_ => (),
};
tx.commit(())
})?;
Ok(())
}
}
/// Describes the state of the reference counter for a block
#[derive(Clone, Copy, Debug)]
pub(crate) enum RcEntry {
/// Present: the block has `count` references, with `count` > 0.
///
/// This is stored as u64::to_be_bytes(count)
Present { count: u64 },
/// Deletable: the block has zero references, and can be deleted
/// once time (returned by now_msec) is larger than at_time
/// (in millis since Unix epoch)
///
/// This is stored as [0u8; 8] followed by u64::to_be_bytes(at_time),
/// (this allows for the data format to be backwards compatible with
/// previous Garage versions that didn't have this intermediate state)
Deletable { at_time: u64 },
/// Absent: the block has zero references, and can be deleted
/// immediately
Absent,
}
impl RcEntry {
fn parse(bytes: &[u8]) -> Self {
if bytes.len() == 8 {
RcEntry::Present {
count: u64::from_be_bytes(bytes.try_into().unwrap()),
}
} else if bytes.len() == 16 {
RcEntry::Deletable {
at_time: u64::from_be_bytes(bytes[8..16].try_into().unwrap()),
}
} else {
panic!("Invalid RC entry: {:?}, database is corrupted. This is an error Garage is currently unable to recover from. Sorry, and also please report a bug.",
bytes
)
}
}
fn parse_opt<V: AsRef<[u8]>>(bytes: Option<V>) -> Self {
bytes
.map(|b| Self::parse(b.as_ref()))
.unwrap_or(Self::Absent)
}
fn serialize(self) -> Option<Vec<u8>> {
match self {
RcEntry::Present { count } => Some(u64::to_be_bytes(count).to_vec()),
RcEntry::Deletable { at_time } => {
Some([u64::to_be_bytes(0), u64::to_be_bytes(at_time)].concat())
}
RcEntry::Absent => None,
}
}
fn increment(self) -> Self {
let old_count = match self {
RcEntry::Present { count } => count,
_ => 0,
};
RcEntry::Present {
count: old_count + 1,
}
}
fn decrement(self) -> Self {
match self {
RcEntry::Present { count } => {
if count > 1 {
RcEntry::Present { count: count - 1 }
} else {
RcEntry::Deletable {
at_time: now_msec() + BLOCK_GC_DELAY.as_millis() as u64,
}
}
}
del => del,
}
}
pub(crate) fn is_zero(&self) -> bool {
matches!(self, RcEntry::Deletable { .. } | RcEntry::Absent)
}
pub(crate) fn is_nonzero(&self) -> bool {
!self.is_zero()
}
pub(crate) fn is_deletable(&self) -> bool {
match self {
RcEntry::Present { .. } => false,
RcEntry::Deletable { at_time } => now_msec() > *at_time,
RcEntry::Absent => true,
}
}
pub(crate) fn is_needed(&self) -> bool {
!self.is_deletable()
}
}
|
