RE: COPY performance on Windows

From: "Ryohei Takahashi (Fujitsu)" <r(dot)takahashi_2(at)fujitsu(dot)com>
To: "Ryohei Takahashi (Fujitsu)" <r(dot)takahashi_2(at)fujitsu(dot)com>, 'Vladlen Popolitov' <v(dot)popolitov(at)postgrespro(dot)ru>
Cc: 'Robert Haas' <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: RE: COPY performance on Windows
Date: 2025-01-14 06:55:04
Message-ID: TY3PR01MB1189178759FA74DB8E508533B82182@TY3PR01MB11891.jpnprd01.prod.outlook.com
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Hi,

I compared the performance between 94f9c08 (previous commit of 82a4edabd2) and 82a4edabd2 with nclient = 8.
The performance is degraded by 8%.

* 94f9c08 (previous commit of 82a4edabd2)
75sec

* 82a4edabd2
81sec

I looked the pg_stat_io view after COPY completed.

* 94f9c08 (previous commit of 82a4edabd2)
backend_type | object | context | reads | read_time | writes | write_time | writebacks | writeback_time | extends | extend_time | op_bytes | hits | evictions | reuses | fsyncs | fsync_time | stats_reset
client backend | relation | bulkwrite | 0 | 0 | 4408399 | 57207.667 | 0 | 0 | 4424783 | 43897.679000000004 | 8192 | 6559989 | 0 | 4408399 | | | 2025-01-14 13:57:29.162001+09

* 82a4edabd2
backend_type | object | context | reads | read_time | writes | write_time | writebacks | writeback_time | extends | extend_time | op_bytes | hits | evictions | reuses | fsyncs | fsync_time | stats_reset
client backend | relation | bulkwrite | 0 | 0 | 4408514 | 112722.993 | 0 | 0 | 4424898 | 33416.076 | 8192 | 5245654 | 0 | 4408514 | | | 2025-01-14 13:54:40.643054+09

By applying 82a4edabd2, extend_time is reduced from 43897ms to 33416ms.
It seems it is the effect of 82a4edabd2.

On the other hand, write_time is increased from 57207ms to 112722ms.
I think write_time is just the time for pwrite(), so I cannot understand why 82a4edabd2 affects write_time.

How do you think about this?

Regards,
Ryohei Takahashi

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