From: Christian Brink <cbrink@r-stream.com>
To: pgsql-performance@postgresql.org
Subject: PostgreSQL upgraded to 8.2 but forcing index scan on query produces faster
Date: Mon, 22 Mar 2010 15:09:11 -0400
Message-ID: <4BA7C057.9090909@r-stream.com> (raw)
I previously posted 'forcing index scan on query produces 16x faster'
and it seemed that the consensus was that 8.0.x series had an issue. I
have upgraded to the highest practical version for our distro. But we
seem to have the same issue.
If I force the 'enable_seqscan' off our actual time is 9ms where if
'enable_seqscan' is on the performance is 2200ms ( the good news is the
Seq Scan query on 8.2 is 1/2 the time of the 8.0 query ).
The paste is below - I reloaded the table from scratch after the 8.2
upgrade. Then I ran a 'REINDEX DATABASE' and a 'VACUUM ANALYZE' (then
ran some queries and reran the vac analyze).
postream=> SELECT version();
version
---------------------------------------------------------------------------------------------------------
PostgreSQL 8.2.11 on i386-redhat-linux-gnu, compiled by GCC gcc (GCC)
4.1.2 20070925 (Red Hat 4.1.2-33)
(1 row)
postream=> SET enable_seqscan = false;
SET
postream=> EXPLAIN ANALYZE
postream-> SELECT si.group1_id as name, sum(si.qty) as count,
sum(si.amt) as amt
postream-> FROM salesitems si, sales s, sysstrings
postream-> WHERE si.id = s.id
postream-> AND si.group1_id != ''
postream-> AND si.group1_id IS NOT NULL
postream-> AND NOT si.void
postream-> AND NOT s.void
postream-> AND NOT s.suspended
postream-> AND s.tranzdate >= (cast('2010-02-15' as date) +
cast(sysstrings.data as time))
postream-> AND s.tranzdate < ((cast('2010-02-15' as date) + 1) +
cast(sysstrings.data as time))
postream-> AND sysstrings.id='net/Console/Employee/Day End Time'
postream-> GROUP BY name;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
HashAggregate (cost=426973.65..426973.86 rows=14 width=35) (actual
time=9.424..9.438 rows=12 loops=1)
-> Nested Loop (cost=0.01..426245.31 rows=97113 width=35) (actual
time=0.653..6.954 rows=894 loops=1)
-> Nested Loop (cost=0.01..2416.59 rows=22477 width=4)
(actual time=0.595..2.150 rows=225 loops=1)
-> Index Scan using sysstrings_pkey on sysstrings
(cost=0.00..8.27 rows=1 width=182) (actual time=0.110..0.112 rows=1 loops=1)
Index Cond: (id = 'net/Console/Employee/Day End
Time'::text)
-> Index Scan using sales_tranzdate_index on sales s
(cost=0.01..1846.40 rows=22477 width=12) (actual time=0.454..1.687
rows=225 loops=1)
Index Cond: ((s.tranzdate >= ('2010-02-15'::date +
(sysstrings.data)::time without time zone)) AND (s.tranzdate <
('2010-02-16'::date + (sysstrings.data)::time without time zone)))
Filter: ((NOT void) AND (NOT suspended))
-> Index Scan using salesitems_pkey on salesitems si
(cost=0.00..18.54 rows=25 width=39) (actual time=0.007..0.013 rows=4
loops=225)
Index Cond: (si.id = s.id)
Filter: (((group1_id)::text <> ''::text) AND (group1_id
IS NOT NULL) AND (NOT void))
Total runtime: 9.585 ms
(12 rows)
postream=> SET enable_seqscan = true;
SET
postream=> EXPLAIN ANALYZE
postream-> SELECT si.group1_id as name, sum(si.qty) as count,
sum(si.amt) as amt
postream-> FROM salesitems si, sales s, sysstrings
postream-> WHERE si.id = s.id
postream-> AND si.group1_id != ''
postream-> AND si.group1_id IS NOT NULL
postream-> AND NOT si.void
postream-> AND NOT s.void
postream-> AND NOT s.suspended
postream-> AND s.tranzdate >= (cast('2010-02-15' as date) +
cast(sysstrings.data as time))
postream-> AND s.tranzdate < ((cast('2010-02-15' as date) + 1) +
cast(sysstrings.data as time))
postream-> AND sysstrings.id='net/Console/Employee/Day End Time'
postream-> GROUP BY name;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
HashAggregate (cost=38315.09..38315.30 rows=14 width=35) (actual
time=2206.531..2206.545 rows=12 loops=1)
-> Hash Join (cost=2697.55..37586.74 rows=97113 width=35) (actual
time=2128.070..2204.048 rows=894 loops=1)
Hash Cond: (si.id = s.id)
-> Seq Scan on salesitems si (cost=0.00..30578.15
rows=890646 width=39) (actual time=0.047..1487.688 rows=901281 loops=1)
Filter: (((group1_id)::text <> ''::text) AND (group1_id
IS NOT NULL) AND (NOT void))
-> Hash (cost=2416.59..2416.59 rows=22477 width=4) (actual
time=1.823..1.823 rows=225 loops=1)
-> Nested Loop (cost=0.01..2416.59 rows=22477 width=4)
(actual time=0.477..1.592 rows=225 loops=1)
-> Index Scan using sysstrings_pkey on
sysstrings (cost=0.00..8.27 rows=1 width=182) (actual time=0.039..0.040
rows=1 loops=1)
Index Cond: (id = 'net/Console/Employee/Day
End Time'::text)
-> Index Scan using sales_tranzdate_index on
sales s (cost=0.01..1846.40 rows=22477 width=12) (actual
time=0.410..1.187 rows=225 loops=1)
Index Cond: ((s.tranzdate >=
('2010-02-15'::date + (sysstrings.data)::time without time zone)) AND
(s.tranzdate < ('2010-02-16'::date + (sysstrings.data)::time without
time zone)))
Filter: ((NOT void) AND (NOT suspended))
Total runtime: 2206.706 ms
(13 rows)
postream=> \d salesitems;
Table "public.salesitems"
Column | Type | Modifiers
--------------+--------------------------+------------------------
id | integer | not null
lineno | smallint | not null
plu | character varying(35) |
qty | numeric(8,3) | not null
amt | numeric(10,2) |
last_updated | timestamp with time zone | default now()
group1_id | character varying(64) |
group2_id | text |
group3_id | text |
void | boolean | not null default false
hash | boolean | not null default false
component | boolean | not null default false
subitem | boolean | not null default false
Indexes:
"salesitems_pkey" PRIMARY KEY, btree (id, lineno)
"idx_si_group_id" btree (group1_id)
"salesitems_last_updated_index" btree (last_updated)
--
Christian Brink
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To: pgsql-performance@postgresql.org
Cc: cbrink@r-stream.com
Subject: Re: PostgreSQL upgraded to 8.2 but forcing index scan on query produces faster
In-Reply-To: <4BA7C057.9090909@r-stream.com>
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