Re: Statistics mismatch between n_live_tup and actual row count

From: tim_wilson <tim(dot)wilson(at)telogis(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: Statistics mismatch between n_live_tup and actual row count
Date: 2012-12-07 02:13:54
Message-ID: 1354846434361-5735588.post@n5.nabble.com
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This drift gets more confusing.

My small table A (60K rows) is not being inserted to (except one or two
rows) it is getting thousands of updates a minute. Analyze and vacuum on the
table are running regularly. But sometimes ,every time the vacuum runs the
reltuples value jumps up. Sometime bloating by 4 times the actualy size of
the table (have seen 10 times)

The impact of this on the query plans is evident straight away. Joins from
all small A to large table B (55 Million rows) on the large B's primary key
start seq scanning.

Some sort of threshold is being hit where the planner believes that the size
of A is big enough that given we are requesting all of A we might as well
scan all of B.

Also even though the table has been clustered and even vacuum full'ed the
relpages value continues to grow.

Any answers?

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