From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | pgsql-committers(at)lists(dot)postgresql(dot)org |
Subject: | pgsql: Count individual SQL commands in pg_restore's --transaction-size |
Date: | 2024-07-29 16:17:34 |
Message-ID: | E1sYT42-001lYg-CR@gemulon.postgresql.org |
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Lists: | pgsql-committers |
Count individual SQL commands in pg_restore's --transaction-size mode.
The initial implementation in commit 959b38d77 counted one action
per TOC entry (except for some special cases for multi-blob BLOBS
entries). This assumes that TOC entries are all about equally
complex, but it turns out that that assumption doesn't hold up very
well in binary-upgrade mode. For example, even after the previous
commit I was able to cause backend bloat with tables having many
inherited constraints. There may be other cases too. (Since no
serious problems have been reported with --single-transaction mode,
we can conclude that the backend copes well with psql's regular
restore scripts; but before 959b38d77 we never ran binary-upgrade
restores with multi-command transactions.)
To fix, count multi-command TOC entries as N actions, allowing the
transaction size to be scaled down when we hit a complex TOC entry.
Rather than add a SQL parser to pg_restore, approximate "multi
command" by counting semicolons in the TOC entry's defn string.
This will be fooled by semicolons appearing in string literals ---
but the error is in the conservative direction, so it doesn't seem
worth working harder. The biggest risk is with function/procedure
TOC entries, but we can just explicitly skip those.
(This is undoubtedly a hack, and maybe someday we'll be able to
revert it after fixing the backend's bloat issues or rethinking
what pg_dump emits in binary upgrade mode. But that surely isn't
a project for v17.)
Thanks to Alexander Korotkov for the let's-count-semicolons idea.
Per report from Justin Pryzby. Back-patch to v17 where txn_size mode
was introduced.
Discussion: https://postgr.es/m/ZqEND4ZcTDBmcv31@pryzbyj2023
Branch
------
REL_17_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/81db073a287842cbf0a17cb32108b214a335670b
Modified Files
--------------
src/bin/pg_dump/pg_backup_archiver.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)
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