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Re: cleanup patches for incremental backup

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-01-27T16:31:09Z
Lists: pgsql-hackers

Attachments

On Sat, Jan 27, 2024 at 11:00:01AM +0300, Alexander Lakhin wrote:
> 24.01.2024 20:46, Robert Haas wrote:
>> This is weird. There's a little more detail in the log file,
>> regress_log_002_blocks, e.g. from the first failure you linked:
>> 
>> [11:18:20.683](96.787s) # before insert, summarized TLI 1 through 0/14E09D0
>> [11:18:21.188](0.505s) # after insert, summarized TLI 1 through 0/14E0D08
>> [11:18:21.326](0.138s) # examining summary for TLI 1 from 0/14E0D08 to 0/155BAF0
>> # 1
>> ...
>> [11:18:21.349](0.000s) #          got: 'pg_walsummary: error: could
>> not open file "/home/nm/farm/gcc64/HEAD/pgsql.build/src/bin/pg_walsummary/tmp_check/t_002_blocks_node1_data/pgdata/pg_wal/summaries/0000000100000000014E0D0800000000155BAF0
>> # 1.summary": No such file or directory'
>> 
>> The "examining summary" line is generated based on the output of
>> pg_available_wal_summaries(). The way that works is that the server
>> calls readdir(), disassembles the filename into a TLI and two LSNs,
>> and returns the result.
> 
> I'm discouraged by "\n1" in the file name and in the
> "examining summary..." message.
> regress_log_002_blocks from the following successful test run on the same
> sungazer node contains:
> [15:21:58.924](0.106s) # examining summary for TLI 1 from 0/155BAE0 to 0/155E750
> [15:21:58.925](0.001s) ok 1 - WAL summary file exists

Ah, I think this query:

	SELECT tli, start_lsn, end_lsn from pg_available_wal_summaries()
		WHERE tli = $summarized_tli AND end_lsn > '$summarized_lsn'

is returning more than one row in some cases.  I attached a quick sketch of
an easy way to reproduce the issue as well as one way to fix it.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid overflow in MaybeRemoveOldWalSummaries().

  2. Revert "Temporary patch to help debug pg_walsummary test failures."

  3. Revise pg_walsummary's 002_blocks test to avoid spurious failures.

  4. Temporary patch to help debug pg_walsummary test failures.

  5. More documentation updates for incremental backup.

  6. Fix typos.

  7. Fix typo.

  8. Try to fix pg_walsummary buildfarm failures.

  9. Repair various defects in dc212340058b4e7ecfc5a7a81ec50e7a207bf288.

  10. Add new pg_walsummary tool.

  11. Add new function pg_get_wal_summarizer_state().

  12. Document WAL summarization information functions.