Re: Compression of bigger WAL records

> On 12 Jan 2025, at 17:43, Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>
> I attach a prototype patch.

Here's v2, now it passes all the tests with wal_debug.

Some stats. On this test

create table a as select random() from generate_series(1,1e7);
select pg_stat_reset_shared('wal'); create index on a(random ); select pg_size_pretty(wal_bytes) from pg_stat_wal;
set wal_compression to 'lz4';
select pg_stat_reset_shared('wal'); create index on a(random ); select pg_size_pretty(wal_bytes) from pg_stat_wal;
set wal_compression to 'pglz';
select pg_stat_reset_shared('wal'); create index on a(random ); select pg_size_pretty(wal_bytes) from pg_stat_wal;
set wal_compression to 'zstd';
select pg_stat_reset_shared('wal'); create index on a(random ); select pg_size_pretty(wal_bytes) from pg_stat_wal;

I observe WAL size of the index:
method HEAD patched
pglz 193 MB 193 MB
lz4 160 MB 132 MB
zstd 125 MB 97 MB

So, for lz4 and zstd this seems to be a significant reduction.

I'm planning to work on improving the patch quality.

Thanks!

Best regards, Andrey Borodin.