On 7/25/17 12:55 AM, Tom Lane wrote:
Tomas Vondra <tomas.von...@2ndquadrant.com> writes:
It seems to me that VACUUM and ANALYZE somewhat disagree on what
exactly reltuples means. VACUUM seems to be thinking that reltuples
= live + dead while ANALYZE apparently believes that reltuples =
live
The question is - which of the reltuples definitions is the right
one? I've always assumed that "reltuples = live + dead" but perhaps
not?
I think the planner basically assumes that reltuples is the live
tuple count, so maybe we'd better change VACUUM to get in step.
Attached is a patch that (I think) does just that. The disagreement was
caused by VACUUM treating recently dead tuples as live, while ANALYZE
treats both of those as dead.
At first I was worried that this will negatively affect plans in the
long-running transaction, as it will get underestimates (due to
reltuples not including rows it can see). But that's a problem we
already have anyway, you just need to run ANALYZE in the other session.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index c5c194a..574ca70 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -1261,7 +1261,7 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
vacrelstats->new_rel_tuples = vac_estimate_reltuples(onerel, false,
nblocks,
vacrelstats->tupcount_pages,
- num_tuples);
+ num_tuples - nkeep);
/*
* Release any remaining pin on visibility map page.
--
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