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help / color / mirror / Atom feedFrom: Peter Geoghegan <[email protected]>
To: Bossart, Nathan <[email protected]>
Cc: John Naylor <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: do only critical work during single-user vacuum?
Date: Mon, 20 Dec 2021 17:17:26 -0800
Message-ID: <CAH2-Wz=Eb-jrhFK6=_WNT6V1JAK-qFOTu_4-yOpAhkEES4VeNA@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
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<[email protected]>
On Thu, Dec 9, 2021 at 8:41 PM Bossart, Nathan <[email protected]> wrote:
> I like the idea of having a built-in function that does the bare
> minimum to resolve wraparound emergencies, and I think providing some
> sort of simple progress indicator (even if rudimentary) would be very
> useful.
If John doesn't have time to work on this during the Postgres 15
cycle, and if nobody else picks it up, then we should at least do the
bare minimum here: force the use of the failsafe in single user mode
(regardless of the age of relfrozenxid/relminmxid, which in general
might not be that old in tables where VACUUM might need to do a lot of
work). Attached quick and dirty patch shows what this would take. If
nothing else, it seems natural to define running any VACUUM in single
user mode as an emergency.
This is really the least we could do -- it's much better than nothing,
but still really lazy^M^M^M^M conservative. I haven't revised the
assumption that the user should do a top-level "VACUUM" in databases
that can no longer allocate XIDs due to wraparound, despite the fact
that we could do far better with moderate effort. Although it might
make sense to commit something like the attached as part of a more
worked out solution (assuming it didn't fully remove single user mode
from the equation, which would be better still).
--
Peter Geoghegan
Attachments:
[application/octet-stream] v1-0001-Always-trigger-failsafe-in-single-user-mode.patch (2.3K, ../CAH2-Wz=Eb-jrhFK6=_WNT6V1JAK-qFOTu_4-yOpAhkEES4VeNA@mail.gmail.com/2-v1-0001-Always-trigger-failsafe-in-single-user-mode.patch)
download | inline diff:
From b7a3ded18d1303e64951439437bcd5925d5c6f44 Mon Sep 17 00:00:00 2001
From: Peter Geoghegan <[email protected]>
Date: Mon, 20 Dec 2021 16:58:40 -0800
Subject: [PATCH v1] Always trigger failsafe in single user mode.
---
src/backend/access/heap/vacuumlazy.c | 12 ++++++++----
src/backend/commands/vacuum.c | 6 +++++-
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index db6becfed..2ba882951 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -2605,6 +2605,14 @@ lazy_check_wraparound_failsafe(LVRelState *vacrel)
vacrel->do_index_cleanup = false;
vacrel->do_rel_truncate = false;
+ /* Stop applying cost limits from this point on */
+ VacuumCostActive = false;
+ VacuumCostBalance = 0;
+
+ /* Single user mode uses failsafe as standard, so no WARNING needed */
+ if (!IsUnderPostmaster)
+ return true;
+
ereport(WARNING,
(errmsg("bypassing nonessential maintenance of table \"%s.%s.%s\" as a failsafe after %d index scans",
get_database_name(MyDatabaseId),
@@ -2615,10 +2623,6 @@ lazy_check_wraparound_failsafe(LVRelState *vacrel)
errhint("Consider increasing configuration parameter \"maintenance_work_mem\" or \"autovacuum_work_mem\".\n"
"You might also need to consider other ways for VACUUM to keep up with the allocation of transaction IDs.")));
- /* Stop applying cost limits from this point on */
- VacuumCostActive = false;
- VacuumCostBalance = 0;
-
return true;
}
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 5c4bc15b4..217bb6965 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1153,7 +1153,8 @@ vacuum_set_xid_limits(Relation rel,
/*
* vacuum_xid_failsafe_check() -- Used by VACUUM's wraparound failsafe
* mechanism to determine if its table's relfrozenxid and relminmxid are now
- * dangerously far in the past.
+ * dangerously far in the past. This is assumed to always be the case when
+ * the backend is run in single user mode.
*
* Input parameters are the target relation's relfrozenxid and relminmxid.
*
@@ -1203,6 +1204,9 @@ vacuum_xid_failsafe_check(TransactionId relfrozenxid, MultiXactId relminmxid)
return true;
}
+ if (!IsUnderPostmaster)
+ return true;
+
return false;
}
--
2.30.2
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Subject: Re: do only critical work during single-user vacuum?
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