On Sat, 14 Jun 2025, Dimitrios Apostolou wrote:
On Fri, 13 Jun 2025, Nathan Bossart wrote:
On Fri, Jun 13, 2025 at 01:00:26AM +0200, Dimitrios Apostolou wrote:
By the way, I might have set the threshold to 1MB in my program, but
lowering it won't show a difference in my test case, since the lseek()s I
was noticing before the patch were mostly 8-16KB forward. Not sure what
is
the defining factor for that. Maybe the compression algorithm, or how
wide
the table is?
I may have missed it, but could you share what the strace looks like with
the patch applied?
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
read(4, "..."..., 12288) = 12288
read(4, "..."..., 4096) = 4096
read(4, "..."..., 8192) = 8192
read(4, "..."..., 4096) = 4096
This was from pg_restoring a zstd-compressed custom format dump.
Out of curiosity I've tried the same with an uncompressed dump
(--compress=none). Surprisingly it seems the blocksize is even smaller.
With my patched pg_restore I only get 4K reads and nothing else on
the strace output.
read(4, "..."..., 4096) = 4096
read(4, "..."..., 4096) = 4096
read(4, "..."..., 4096) = 4096
read(4, "..."..., 4096) = 4096
read(4, "..."..., 4096) = 4096
read(4, "..."..., 4096) = 4096
The unpatched pg_restore gives me the weirdest output ever:
read(4, "..."..., 4096) = 4096
lseek(4, 98527916032, SEEK_SET) = 98527916032
lseek(4, 98527916032, SEEK_SET) = 98527916032
lseek(4, 98527916032, SEEK_SET) = 98527916032
lseek(4, 98527916032, SEEK_SET) = 98527916032
lseek(4, 98527916032, SEEK_SET) = 98527916032
lseek(4, 98527916032, SEEK_SET) = 98527916032
[ ... repeats about 80 times ...]
read(4, "..."..., 4096) = 4096
lseek(4, 98527920128, SEEK_SET) = 98527920128
lseek(4, 98527920128, SEEK_SET) = 98527920128
lseek(4, 98527920128, SEEK_SET) = 98527920128
lseek(4, 98527920128, SEEK_SET) = 98527920128
[ ... repeats ... ]
Seeing this, I think we should really consider raising the pg_dump block
size like Tom suggested on a previous thread.
Dimitris
