Greetings, We've been using postgreSQL for a few years. This is my first post here and first real dive into query plans.
A description of what you are trying to achieve and what results you expect.: Query results of nested joins of table. Results are correct - just takes a long time with selected plan. PostgreSQL version number you are running: PostgreSQL 9.2.3 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.6 20120305 (Red Hat 4.4.6-4), 64-bit How you installed PostgreSQL: yum, using PGDG repo (package postgresql92-server-9.2.3-2PGDG.rhel6.x86_64 and friends) Changes made to the settings in the postgresql.conf file DateStyle = ISO, MDY default_tablespace = esc_data default_text_search_config = pg_catalog.english effective_cache_size = 24GB lc_messages = en_US.UTF-8 lc_monetary = en_US.UTF-8 lc_numeric = en_US.UTF-8 lc_time = en_US.UTF-8 listen_addresses = 0.0.0.0 log_connections = on log_destination = stderr log_disconnections = on log_line_prefix = %t %c log_rotation_age = 1d log_timezone = US/Eastern logging_collector = on maintenance_work_mem = 96MB max_connections = 100 search_path = "$user", esc_funcs, public shared_buffers = 8GB TimeZone = US/Eastern track_functions = all track_io_timing = on Operating system and version: Red Hat Enterprise Linux Server release 6.4 (Santiago) What program you're using to connect to PostgreSQL: java(jdbc) and psql Is there anything relevant or unusual in the PostgreSQL server logs?: no The issue is similar on PostgreSQL 9.0.5 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.4.real (Ubuntu 4.4.3-4ubuntu5) 4.4.3 on Ubuntu 10.04 64-bit although we're doing troubleshooting on our new RHEL server. We have a particular query that takes about 75 minutes to complete. The selected execution plan estimates 1 row from several of the outermost results so picks nested loop join resolutions. That turns out to be a bad choice since actual row counts are in the thirty to fifty thousand range. original selected plan: http://explain.depesz.com/s/muR SQL: http://pastebin.com/f40Xp0JM I set enable_nestloop=false to hint at the planner not to use nested loop. That resulted in 13 second runtime. It appears this plan was considered originally but estimated cost was higher than the plan above. enable_nestloop=false: http://explain.depesz.com/s/mAa SQL: http://pastebin.com/CgcSe7r6 We tried rewriting the query using WITH clauses. That took 82 seconds but plan thought it would take much longer. using with clauses: http://explain.depesz.com/s/GEZ SQL: http://pastebin.com/ZRvRK2TV We have been looking into the issue to the best of our ability but can't figure out how to help the planner. I've looked at the planner source some and see where row count is set to 1 if it's <= 1. I haven't found where it's set yet but presume it was unable to determine the result set row count and defaulted to 1. I've run analyze manually and tried it with default_statistics_target=10000 to see if that helped. It didn't. The table is static - no new rows are being added and there is no other load on the database. schema dump: http://pastebin.com/pUU0BJvr What can we do to help the planner estimate better? Thanks in advance, Marty Frasier
