PostgreSQL - Tipps und Tricks: Unterschied zwischen den Versionen

Version vom 9. Januar 2009, 13:23 Uhr

Siehe auch:

• PostgreSQL
• PostGIS und PostgreSQL - Tipps und Tricks

Quickreference

Im Aufbau...

• Start pgsl-Client:

 $ psql.exe -h localhost -p 5432 template1 "postgres"

PostgreSQL SQL

Version:

 select version();

Anfrage des Geometrie-Typs ('the_geom' ist der Name des Geometrie-Felds):

 SELECT *
   FROM sometable
   WHERE GeometryType(the_geom) = 'GEOMETRYCOLLECTION'

Problem mit Datenfelder (for < 8.3):

 SELECT the_geom ... (end_date - NOW() >= 10) AS GREEN 
   AND (end_date - NOW() < 0) AS RED ... FROM ...

Casting changes in >= 8.3:

 SELECT the_geom ... (end_date - NOW() >= '10 DAYS'::INTERVAL) AS GREEN 
   AND (end_date - NOW() < '0'::INTERVAL) AS RED ... FROM ...

 SELECT the_geom ...
   EXTRACT(DAY FROM (end_date - NOW()) >= 10) AS GREEN
   AND EXTRACT(DAY FROM (end_date - NOW()) < 0) AS RED ... FROM ...

Konfiguration

Die pg_hba.conf kann so eingestellt werden, dass bei der Ausführung von PostgreSQL-Kommandozeilen-Tools kein Passwort übertragen werden muss.

Bsp mit 127.0.0.1: Anstelle

 # IPv4 local connections:
 host    all         all         127.0.0.1/32          md5

neu:

 # IPv4 local connections:
 host    all         all         127.0.0.1/32          trust

PostgreSQL optimieren

1. Make sure you have (spatial) indexes on your tables.
2. Cluster on (spatial) indexes tends to improve performance but mostly good for static spatial data.
3. PostGIS: A spatial index is more effective on small geometries than larger geometries even for MySQL.
4. EXPLAIN ANALYZE is your friend -- especially PgAdmin III Graphical Explain - will pinpoint when indexes are not being used and what navigation strategies are being used.
5. posgresql.conf - fiddling with that a lot has been written -- particularly work_mem is important.
6. Then there is a whole science on how you write sql queries. In general for PostgreSQL - you can force PostgreSQL to materialize subselects by putting in an ORDER BY and in general a subselect tends to force the planner to evaluate those as a single unit of work, which tends to improve speed in many cases.