Peter Geoghegan <> wrote:
In Alik's workload, there are two queries: One UPDATE, one SELECT.  Even
though the bloated index was a unique index, and so still gets
_bt_check_unique() item killing, the regression is still going to block
LP_DEAD cleanup by the SELECTs, which seems like it might be quite
important there.  After all, _bt_check_unique() cleanup has to happen
with an exclusive buffer lock held, whereas the kill_prior_tuple stuff
happens with only a shared buffer lock held.  It's not hard to imaging
that there will be a whole lot less LP_DEAD setting, overall.

Actually, there is a much bigger reason why SELECT statement LP_DEAD
killing matters more to Alik's workload than _bt_check_unique() LP_DEAD
killing: The UPDATE query itself does not affect indexed columns. Most
UPDATEs are actually HOT-safe (despite the degree of index bloat we
see), and so most UPDATEs will never reach _bt_check_unique().

Peter Geoghegan

Sent via pgsql-hackers mailing list (
To make changes to your subscription:

Reply via email to