diff options
author | Michael Paquier | 2024-11-11 00:02:30 +0000 |
---|---|---|
committer | Michael Paquier | 2024-11-11 00:02:30 +0000 |
commit | 5d4298e75f252b162008ad0475f29349023573cb (patch) | |
tree | f878fbd8ff87b3e264139e85daf171f9c298cb79 | |
parent | 29d66b2d2f80dba0ac7fa5453d4da2dfbdd5ed2b (diff) |
pg_stat_statements: Avoid some locking during PGSS entry scans
A single PGSS entry's spinlock is used to be able to modify "counters"
without holding pgss->lock exclusively, as mentioned at the top of
pg_stat_statements.c and within pgssEntry.
Within a single pgssEntry, stats_since and minmax_stats_since are never
modified without holding pgss->lock exclusively, so there is no need to
hold an entry's spinlock when reading stats_since and
minmax_stats_since, as done when scanning all the PGSS entries for
function calls of pg_stat_statements().
This also restores the consistency between the code and the comments
about the entry's spinlock usage. This change is a performance
improvement (it can be argued that this is a logic bug), so there is no
need for a backpatch. This saves two instructions from being read while
holding an entry's spinlock.
Author: Karina Litskevich
Reviewed-by: Michael Paquier, wenhui qiu
Discussion: https://postgr.es/m/CACiT8ibhCmzbcOxM0v4pRLH3abk-95LPkt7_uC2JMP+miPjxsg@mail.gmail.com
-rw-r--r-- | contrib/pg_stat_statements/pg_stat_statements.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c index 1798e1d016..49c657b3e0 100644 --- a/contrib/pg_stat_statements/pg_stat_statements.c +++ b/contrib/pg_stat_statements/pg_stat_statements.c @@ -1869,9 +1869,14 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo, /* copy counters to a local variable to keep locking time short */ SpinLockAcquire(&entry->mutex); tmp = entry->counters; + SpinLockRelease(&entry->mutex); + + /* + * The spinlock is not required when reading these two as they are + * always updated when holding pgss->lock exclusively. + */ stats_since = entry->stats_since; minmax_stats_since = entry->minmax_stats_since; - SpinLockRelease(&entry->mutex); /* Skip entry if unexecuted (ie, it's a pending "sticky" entry) */ if (IS_STICKY(tmp)) |