hawdb-storage 0.13.0

An embedded Rust graph database for local data-plane workloads
Documentation 
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

// Copyright 2026 Nowledge
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Bounded, generation-reframed post-snapshot WAL preparation.

use super::{DurableStore, PreparedCheckpoint};
use crate::durability::durable_replace_file;
use crate::error::{HawDBError, Result};
use crate::file_io::{self as fs, File};
use crate::store::{
    encode_binary_wal_header, encode_binary_wal_record, frame_binary_wal_record,
    wal_generation_file, WalCursorEvent, WalRecordCursor, WAL_BINARY_FILE_HEADER_BYTES,
};
use std::io::Write;

/// Receipt for a private candidate; not evidence of checkpoint publication.
#[doc(hidden)]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct CheckpointWalTail {
    pub captured_commit_epoch: u64,
    pub captured_next_lsn: u64,
    pub captured_wal_generation: u64,
    pub captured_wal_bytes: u64,
    pub candidate_wal_bytes: u64,
    pub entries: u64,
}

impl DurableStore {
    pub(in crate::store) fn checkpoint_tail_record_limit(&self) -> Option<usize> {
        self.max_record_bytes
    }

    pub(in crate::store) fn prepare_checkpoint_wal_tail(
        &self,
        prepared: &PreparedCheckpoint,
        commit_epoch: u64,
    ) -> Result<CheckpointWalTail> {
        if self.read_only || self.wal_sync_group_active() {
            return Err(HawDBError::Storage(
                "checkpoint suffix capture requires a writable, fully flushed commit boundary"
                    .into(),
            ));
        }
        if self.checkpoint_epoch != prepared.source_checkpoint_epoch
            || self.wal_generation != prepared.source_wal_generation
            || self.wal_bytes < prepared.source_wal_bytes
            || self.next_lsn < prepared.source_next_lsn
            || commit_epoch < prepared.source_commit_epoch
            || self.next_lsn - prepared.source_next_lsn
                != commit_epoch - prepared.source_commit_epoch
            || prepared.generation <= self.wal_generation
        {
            return Err(HawDBError::Storage(
                "checkpoint suffix source identity changed; retain the authoritative WAL".into(),
            ));
        }
        let path = self
            .root_path
            .join(wal_generation_file(prepared.generation));
        let temporary = path.with_extension("hawdb.tail.tmp");
        let result = (|| {
            let header = encode_binary_wal_header(prepared.generation, prepared.source_next_lsn);
            let mut output = File::create(&temporary)?;
            output.write_all(&header)?;
            let mut bytes = header.len() as u64;
            let mut expected_lsn = prepared.source_next_lsn;
            let mut epoch = prepared.source_commit_epoch;
            if expected_lsn < self.next_lsn {
                let mut cursor = WalRecordCursor::open_range(
                    &self.wal_path,
                    self.max_record_bytes,
                    self.wal_generation,
                    self.wal_replay_start_lsn,
                    prepared
                        .source_wal_bytes
                        .max(WAL_BINARY_FILE_HEADER_BYTES as u64),
                    self.wal_bytes,
                )?;
                loop {
                    let entry = match cursor.next()? {
                        WalCursorEvent::Entry { entry, .. } => entry,
                        WalCursorEvent::Eof => break,
                        WalCursorEvent::Corrupt { reason, .. }
                        | WalCursorEvent::TornTail { reason, .. } => {
                            return Err(HawDBError::StorageIntegrity(format!(
                                "checkpoint suffix is not a complete committed interval: {reason}"
                            )));
                        }
                    };
                    if entry.lsn != expected_lsn || expected_lsn >= self.next_lsn {
                        return Err(HawDBError::StorageIntegrity(
                            "checkpoint suffix has a noncontiguous or unexpected LSN".into(),
                        ));
                    }
                    epoch = epoch.checked_add(1).ok_or_else(|| {
                        HawDBError::StorageIntegrity("checkpoint suffix epoch overflow".into())
                    })?;
                    let payload = encode_binary_wal_record(&entry, epoch)?;
                    let framed = frame_binary_wal_record(
                        prepared.generation,
                        &payload,
                        bytes - WAL_BINARY_FILE_HEADER_BYTES as u64,
                    );
                    output.write_all(&framed)?;
                    bytes = bytes.checked_add(framed.len() as u64).ok_or_else(|| {
                        HawDBError::Storage("checkpoint suffix byte count overflow".into())
                    })?;
                    if self.max_wal_bytes.is_some_and(|limit| bytes > limit) {
                        return Err(HawDBError::Storage(
                            "reframed checkpoint suffix exceeds the configured WAL budget".into(),
                        ));
                    }
                    expected_lsn = expected_lsn.checked_add(1).ok_or_else(|| {
                        HawDBError::StorageIntegrity("checkpoint suffix LSN overflow".into())
                    })?;
                }
            }
            if expected_lsn != self.next_lsn || epoch != commit_epoch {
                return Err(HawDBError::StorageIntegrity(
                    "checkpoint suffix does not cover every captured commit".into(),
                ));
            }
            // A completed prefix with unexpected bytes after the final LSN is
            // rejected by the bounded reader/count checks above. All captured
            // suffix bytes become durable before any future selector change.
            output.sync_all()?;
            drop(output);
            durable_replace_file(&temporary, &path)?;
            Ok(CheckpointWalTail {
                captured_commit_epoch: commit_epoch,
                captured_next_lsn: self.next_lsn,
                captured_wal_generation: self.wal_generation,
                captured_wal_bytes: self.wal_bytes,
                candidate_wal_bytes: bytes,
                entries: self.next_lsn - prepared.source_next_lsn,
            })
        })();
        if result.is_err() {
            // This temporary file is owned by the serialized checkpoint job.
            // Leave the already prepared generation and authoritative WAL intact.
            match fs::remove_file(&temporary) {
                Ok(()) => {}
                Err(error) if error.kind() == std::io::ErrorKind::NotFound => {}
                Err(error) => return Err(error.into()),
            }
        }
        result
    }
}