Re: [HACKERS] Hooks to track changed pages for backup purposes

On Thu, Aug 31, 2017 at 9:02 AM, Andrey Borodin <x4mmm@yandex-team.ru> wrote:
> When we have accumulated diff blocknumbers for most of segments we can significantly speed up method of WAL scanning.
Ifwe have blocknumbers for all segments we can skip WAL scanning at all.
 

Have you measured that the WAL scanning is actually a significant
issue? As a quick experiment I hacked up pg_waldump to just dump block
references to stdout in binary format. It scanned 2.8GB of WAL in 3.17
seconds, outputting 9.3M block refs per second. WAL was generated with
pgbench, synchronous commit off, using 4 cores for 10 minutes - making
the ratio of work from generating WAL to parsing it be about 750:1.

Regards,
Ants Aasma


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