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+mipj...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/5d4298e75f252b162008ad0475f29349023573cb Modified Files -------------- contrib/pg_stat_statements/pg_stat_statements.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
