On 22.12.2010 02:56, Merlin Moncure wrote:
On Tue, Dec 21, 2010 at 7:45 PM, Tom Lane<t...@sss.pgh.pa.us> wrote:
Merlin Moncure<mmonc...@gmail.com> writes:
Attached is an incomplete patch disabling hint bits based on compile
switch. ...
So far, at least doing pgbench runs and another test designed to
exercise clog lookups, the performance loss of always doing full
lookup hasn't materialized.
The standard pgbench test would be just about 100% useless for stressing
this, because its net database activity is only about one row
touched/updated per query. You need a test case that hits lots of rows
per query, else you're just measuring parse+plan+network overhead.
right -- see the attached clog_stress.sql above. It creates a script
that inserts records in blocks of 10000, deletes half of them, and
vacuums. Neither the execution of the script nor a seq scan following
its execution showed an interesting performance difference (which I am
arbitrarily calling 5% in either direction). Like I said though, I
don't trust the patch or the results yet.
Make sure you have a good mix of different xids in the table,
TransactionLogFetch has a one-item cache so repeatedly checking the same
xid is much faster than the general case.
Perhaps run pgbench for a while, and then do "SELECT COUNT(*)" on the
resulting tables.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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