Branching off from [0], here is a for-discussion patch about some
corrections for the pg_resetwal -c (--commit-timestamp-ids) option.
First, in the documentation for finding a manual value for the -c option
based on the files present in the data directory, it was missing a
multiplier, like for the other SLRU-based values, and also missing the
mention of adding one for the upper value. The value I came up with is
computed as
SLRU_PAGES_PER_SEGMENT * COMMIT_TS_XACTS_PER_PAGE = 13088 = 0x3320
Second, the present pg_resetwal code hardcodes the minimum value as 2,
which is FrozenTransactionId, but it's not clear why that is allowed.
Maybe we should change that to FirstNormalTransactionId, which matches
other xid-related options in pg_resetwal.
Thoughts?
[0]:
https://www.postgresql.org/message-id/flat/0f3ab4a1-ae80-56e8-3426-6b4a02507...@eisentraut.orgFrom c092e8767cad0618feee6e6a76071aeb9df3efad Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Thu, 28 Sep 2023 15:43:01 +0200
Subject: [PATCH] WIP: pg_resetwal: Corrections around -c option
In the documentation for finding a manual value for the -c option
based on the files present in the data directory, it was missing a
multiplier, like for the other SLRU-based values, and also missing the
mention of adding one for the upper value. The value mentioned here
is computed as
SLRU_PAGES_PER_SEGMENT * COMMIT_TS_XACTS_PER_PAGE = 13088 = 0x3320
Also, the present pg_resetwal code hardcodes the minimum value as 2,
which is FrozenTransactionId, but it's not clear why that is allowed.
Change that to FirstNormalTransactionId, which matches other
xid-related options in pg_resetwal.
---
doc/src/sgml/ref/pg_resetwal.sgml | 7 ++++---
src/bin/pg_resetwal/pg_resetwal.c | 12 ++++++------
2 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/doc/src/sgml/ref/pg_resetwal.sgml
b/doc/src/sgml/ref/pg_resetwal.sgml
index 08cd3ce5fc..40ea1ff724 100644
--- a/doc/src/sgml/ref/pg_resetwal.sgml
+++ b/doc/src/sgml/ref/pg_resetwal.sgml
@@ -183,11 +183,12 @@ <title>Options</title>
A safe value for the oldest transaction ID for which the commit time can
be retrieved (first part) can be determined by looking
for the numerically smallest file name in the directory
- <filename>pg_commit_ts</filename> under the data directory. Conversely,
a safe
+ <filename>pg_commit_ts</filename> under the data directory and then
+ multiplying by 13088 (0x3320). Conversely, a safe
value for the newest transaction ID for which the commit time can be
retrieved (second part) can be determined by looking for the numerically
- greatest file name in the same directory. The file names are in
- hexadecimal.
+ greatest file name in the same directory, adding one, and then
+ multiplying by 13088 (0x3320). The file names are in hexadecimal.
</para>
</listitem>
</varlistentry>
diff --git a/src/bin/pg_resetwal/pg_resetwal.c
b/src/bin/pg_resetwal/pg_resetwal.c
index 47e05bd2c9..b3fb94dfbe 100644
--- a/src/bin/pg_resetwal/pg_resetwal.c
+++ b/src/bin/pg_resetwal/pg_resetwal.c
@@ -211,13 +211,13 @@ main(int argc, char *argv[])
exit(1);
}
- if (set_oldest_commit_ts_xid < 2 &&
- set_oldest_commit_ts_xid != 0)
- pg_fatal("transaction ID (-c) must be
either 0 or greater than or equal to 2");
+ if (set_oldest_commit_ts_xid <
FirstNormalTransactionId &&
+ set_oldest_commit_ts_xid !=
InvalidTransactionId)
+ pg_fatal("transaction ID (-c) must be
either %u or greater than or equal to %u", InvalidTransactionId,
FirstNormalTransactionId);
- if (set_newest_commit_ts_xid < 2 &&
- set_newest_commit_ts_xid != 0)
- pg_fatal("transaction ID (-c) must be
either 0 or greater than or equal to 2");
+ if (set_newest_commit_ts_xid <
FirstNormalTransactionId &&
+ set_newest_commit_ts_xid !=
InvalidTransactionId)
+ pg_fatal("transaction ID (-c) must be
either %u or greater than or equal to %u", InvalidTransactionId,
FirstNormalTransactionId);
break;
case 'o':
--
2.42.0
