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base repository: postgres/postgres
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head repository: baotiao/postgres
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  • 4 commits
  • 12 files changed
  • 3 contributors

Commits on Feb 7, 2026

  1. Add double write buffer (DWB) for torn page protection 

    Implement a double write buffer mechanism as an alternative to full page
writes (FPW). When enabled, dirty pages are written to a dedicated DWB
file before being written to the data files. This provides protection
against torn pages without requiring full page images in WAL.

Key benefits over FPW:
- Dramatically reduced WAL volume (up to 98% reduction in IO-bound workloads)
- Lower network bandwidth for replication
- Faster WAL replay during recovery

The implementation includes:
- New GUC parameters: double_write_buffer (bool) and
  double_write_buffer_size (int, default 64MB)
- DWB files stored in pg_dwbuf/ directory
- Integration with checkpoint for proper flush ordering
- Per-process file descriptor management for correctness

Performance testing shows:
- WAL reduction: 270GB -> 4.6GB (58x reduction) in IO-bound scenarios
- TPS overhead: ~1% compared to no protection
- Comparable TPS to FPW with vastly reduced WAL

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
    @claude
    zongzhi.czz and claude committed Feb 7, 2026
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  2. Fix DWB process handling and skip FPW when DWB enabled 

    - Skip full page writes when double write buffer is enabled since DWB
  already provides torn page protection
- Fix file descriptor handling after fork by tracking process ID
- Initialize DWB in checkpointer process
- Improve batch synchronization in DWBufPostCheckpoint
- Add DWB shared memory initialization in ipci.c

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
    @claude
    zongzhi.czz and claude committed Feb 7, 2026
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  3. Add Claude Code configuration 

    Add local settings for Claude Code with permission allowlist for
common development and testing commands.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
    @claude
    zongzhi.czz and claude committed Feb 7, 2026
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  4. Fix critical correctness bugs in double write buffer (DWB) 

    Fix several issues that made the DWB feature unsafe:

1. CRC computation: Move crc to first field of DWBufPageSlot and zero
   it before computing, so the stale crc value is excluded from the
   CRC range. Previously verification would always fail.

2. Fsync before data file writes: DWB pages must be durable before
   data file writes begin. Add per-page DWBufFlushFile() for
   non-checkpoint writes (bgwriter/backend eviction), and batch
   DWBufFlush() in BufferSync for checkpoint writes.

3. Checkpoint integration: Wire up DWBufPreCheckpoint/PostCheckpoint
   calls in CreateCheckPoint and CreateRestartPoint — they existed
   but were never called.

4. Recovery path: Wire up DWBufRecoveryInit in StartupXLOG to build
   recovery hash, DWBufRecoverPage in buffer_readv_complete to
   recover torn pages, and DWBufRecoveryFinish after FinishWalRecovery.

5. Backup FPW: Keep full_page_writes enabled when a backup is running
   even with DWB on, since pg_basebackup doesn't copy DWB files.

6. Slot overflow: Add bounds check when write_pos >= num_slots,
   flush and wrap instead of overwriting valid data.

7. PostCheckpoint race: Add resetting flag to prevent concurrent
   DWBufWritePage calls during position reset.

8. Build/initdb: Add dwbuf.c to meson.build, pg_dwbuf to initdb
   subdirs array.

9. Minor: Remove unused old_batch_id, fix %ld format string cast.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
    @baotiao @claude
    baotiao and claude committed Feb 7, 2026
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