From: Willy-Bas Loos [mailto:willybas@xxxxxxxxx] Sent: Wednesday, June 26, 2013 3:04 PM To: Igor Neyman Cc: pgsql-performance@xxxxxxxxxxxxxx Subject: Re: seqscan for 100 out of 3M rows, index present nope $ grep ^[^#] /etc/postgresql/9.1/main/postgresql.conf|grep -e ^[^[:space:]] data_directory = '/var/lib/postgresql/9.1/main' # use data in another directory hba_file = '/etc/postgresql/9.1/main/pg_hba.conf' # host-based authentication file ident_file = '/etc/postgresql/9.1/main/pg_ident.conf' # ident configuration file external_pid_file = '/var/run/postgresql/9.1-main.pid' # write an extra PID file port = 5432 # (change requires restart) max_connections = 100 # (change requires restart) unix_socket_directory = '/var/run/postgresql' # (change requires restart) ssl = true # (change requires restart) shared_buffers = 2GB # min 128kB work_mem = 100MB # min 64kB maintenance_work_mem = 256MB # min 1MB synchronous_commit = off # synchronization level; on, off, or local checkpoint_segments = 10 # in logfile segments, min 1, 16MB each log_line_prefix = '%t ' # special values: datestyle = 'iso, mdy' lc_messages = 'en_US.UTF-8' # locale for system error message lc_monetary = 'en_US.UTF-8' # locale for monetary formatting lc_numeric = 'en_US.UTF-8' # locale for number formatting lc_time = 'en_US.UTF-8' # locale for time formatting default_text_search_config = 'pg_catalog.english' -- You could change this setting on session level, and prove yourself or query optimizer right (or wrong :) Igor Neyman ... ... Aggregate (cost=60836.71..60836.72 rows=1 width=0) (actual time=481.526..481.526 rows=1 loops=1) -> Hash Join (cost=1296.42..60833.75 rows=1184 width=0) (actual time=317.403..481.513 rows=17 loops=1) Hash Cond: (d2.gid = g2.gid) -> Seq Scan on d2 (cost=0.00..47872.54 rows=3107454 width=8) (actual time=0.013..231.707 rows=3107454 loops=1) -> Hash (cost=1290.24..1290.24 rows=494 width=8) (actual time=0.207..0.207 rows=121 loops=1) Buckets: 1024 Batches: 1 Memory Usage: 5kB -> Index Scan using g_blok on g2 (cost=0.00..1290.24 rows=494 width=8) (actual time=0.102..0.156 rows=121 loops=1) Index Cond: (k = 1942) Total runtime: 481.600 ms Here's the DDL: create table g2 (gid bigint primary key, k integer); create table d2 (id bigint primary key, gid bigint); --insert into g2 (...) --insert into d2 (...) create index g_blok on g2(blok); create index d_gid on d2(gid); alter table d2 add constraint d_g_fk foreign key (gid) references g2 (gid); analyze d2; analyze g2; Any advice? Cheers, Willy-Bas Loos -- So, did you try to set: enable_seqscan = off and see if different execution plan is more efficient? Igor Neyman -- "Quality comes from focus and clarity of purpose" -- Mark Shuttleworth -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
