From 414ed1ca232134e512ecfed1849f092f24f2a27a Mon Sep 17 00:00:00 2001 From: Fujii Masao Date: Wed, 19 Feb 2020 20:37:26 +0900 Subject: [PATCH] Fix mesurement of elapsed time during truncating heap in VACUUM. VACUUM may truncate heap in several batches. The activity report is logged for each batch, and contains the number of pages in the table before and after the truncation, and also the elapsed time during the truncation. Previously the elapsed time reported in each batch was the total elapsed time since starting the truncation until finishing each batch. For example, if the truncation was processed dividing into three batches, the second batch reported the accumulated time elapsed during both first and second batches. This is strange and confusing because the number of pages in the table reported together is not total. Instead, each batch should report the time elapsed during only that batch. The cause of this issue was that the resource usage snapshot was initialized only at the beginning of the truncation and was never reset later. This commit fixes the issue by changing VACUUM so that the resource usage snapshot is reset at each batch. Back-patch to all supported branches. Reported-by: Tatsuhito Kasahara Author: Tatsuhito Kasahara Reviewed-by: Masahiko Sawada, Fujii Masao Discussion: https://postgr.es/m/CAP0=ZVJsf=NvQuy+QXQZ7B=ZVLoDV_JzsVC1FRsF1G18i3zMGg@mail.gmail.com --- src/backend/commands/vacuumlazy.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index 5649a70800..7c00418578 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -1809,11 +1809,8 @@ lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats) { BlockNumber old_rel_pages = vacrelstats->rel_pages; BlockNumber new_rel_pages; - PGRUsage ru0; int lock_retry; - pg_rusage_init(&ru0); - /* Report that we are now truncating */ pgstat_progress_update_param(PROGRESS_VACUUM_PHASE, PROGRESS_VACUUM_PHASE_TRUNCATE); @@ -1823,6 +1820,10 @@ lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats) */ do { + PGRUsage ru0; + + pg_rusage_init(&ru0); + /* * We need full exclusive lock on the relation in order to do * truncation. If we can't get it, give up rather than waiting --- we