On Wed, Dec 9, 2009 at 12:36 AM, Takahiro Itagaki
<itagaki.takah...@oss.ntt.co.jp> wrote:
> Note that the patch also removes buffer counters from log_statement_stats,
> but we only have brief descriptions about the options. Our documentation
> say nothing about buffer counters, so I didn't modify those lines in sgml.
> http://developer.postgresql.org/pgdocs/postgres/runtime-config-statistics.html#RUNTIME-CONFIG-STATISTICS-MONITOR
I'm not sure whether this is a good idea or not. Let me read the
patch. I'm not sure an EXPLAIN option is really an adequate
substitute for log_statement_stats - the latter will let you get stats
for all of your queries automatically, I believe, and might still be
useful as a quick and dirty tool.
> IMHO, we could remove those options completely because we can use
> EXPLAIN BUFFERS and DTrace probes instead of them.
We certainly should NOT count on dtrace as a substitute for anything.
It's not available on Windows, or all other platforms either.
> =# EXPLAIN (BUFFERS, ANALYZE) SELECT *
> FROM pgbench_accounts a, pgbench_branches b
> WHERE a.bid = b.bid AND abalance > 0 ORDER BY abalance;
> QUERY PLAN
> ------------------------------------------------------------------------------------------------------------------------------
> Sort (cost=2891.03..2891.04 rows=1 width=461) (actual time=22.494..22.494
> rows=0 loops=1)
> Sort Key: a.abalance
> Sort Method: quicksort Memory: 25kB
> Blocks: (shared hit=96 read=1544 written=0) (local hit=0 read=0 written=0)
> (temp read=0 written=0)
> -> Nested Loop (cost=0.00..2891.02 rows=1 width=461) (actual
> time=22.488..22.488 rows=0 loops=1)
> Join Filter: (a.bid = b.bid)
> Blocks: (shared hit=96 read=1544 written=0) (local hit=0 read=0
> written=0) (temp read=0 written=0)
> -> Seq Scan on pgbench_accounts a (cost=0.00..2890.00 rows=1
> width=97) (actual time=22.486..22.486 rows=0 loops=1)
> Filter: (abalance > 0)
> Blocks: (shared hit=96 read=1544 written=0) (local hit=0 read=0
> written=0) (temp read=0 written=0)
> -> Seq Scan on pgbench_branches b (cost=0.00..1.01 rows=1
> width=364) (never executed)
> Blocks: (shared hit=0 read=0 written=0) (local hit=0 read=0
> written=0) (temp read=0 written=0)
> Total runtime: 22.546 ms
> (13 rows)
I still think this is a bad format. Instead of putting "(" and ")"
around each phrase, can't we just separate them with a "," or ";"?
The filter uses parentheses in a mathematical way, for grouping
related items. Not all filters are surrounded by parentheses
(consider a filter like "WHERE x", x being a boolean column) and some
will have multiple sets, if there are ANDs and ORs in there.
...Robert
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