postgresql-performance

I am not very familiar with looking at EXPLAIN ANALYZE results, I have a huge problem with my queries being too slow. I have tried to read up on how to interpret results from an explain queries, but I still don't know what I should be looking for, and what might be wrong. I have a feeling that there is some big red light flashing somewhere, I just don't see it. So the query is pretty simple, it looks like this: EXPLAIN ANALYZE SELECT "cars".* FROM "cars" WHERE "cars"."sales_state" = 'onsale' AND "cars"."brand" = 'BMW' AND "cars"."model_name" = '318i' AND "cars"."has_auto_gear" = TRUE LIMIT 25

I have a star schema here and I am querying the fact table and would like to join one very small dimension table. I can't really explain the following: EXPLAIN ANALYZE SELECT COUNT(impression_id), imp.os_id FROM bi.impressions imp GROUP BY imp.os_id; QUERY PLAN -------------------------------------------------------------------------------------------------------------------------------------- HashAggregate (cost=868719.08..868719.24 rows=16 width=10) (actual time=12559.462..12559.466 rows=26 loops=1) -> Seq Scan on impressions imp (cost=0.00..690306.72 rows=35682472 width=10) (actual time=0

I have to optimize queries by tuning basic PostgreSQL server configuration parameters. In documentation I've came across the work_mem parameter. Then I checked how changing this parameter would influence performance of my query (using sort). I measured query execution time with various work_mem settings and was very disappointed. The table on which I perform my query contains 10,000,000 rows and there are 430 MB of data to sort. ( Sort Method: external merge Disk: 430112kB ). With work_mem = 1MB , EXPLAIN output is: Total runtime: 29950.571 ms (sort takes about 19300 ms). Sort (cost=4032588.78

I need to delete about 2 million rows from my PG database. I have a list of IDs that I need to delete. However, any way I try to do this is taking days. I tried putting them in a table and doing it in batches of 100. 4 days later, this is still running with only 297268 rows deleted. (I had to select 100 id's from an ID table, delete where IN that list, delete from ids table the 100 I selected). I tried: DELETE FROM tbl WHERE id IN (select * from ids) That's taking forever, too. Hard to gauge how long, since I can't see it's progress till done, but the query was still running after 2 days. Just

What if I want to search for a single row in a table with a decrementing precision, e.g. like this: SELECT * FROM image WHERE name LIKE 'text' AND group_id = 10 LIMIT 1 When this gives me no result, try this one: SELECT * FROM image WHERE name LIKE 'text' LIMIT 1 And when this gives me no result, try this one: SELECT * FROM image WHERE group_id = 10 LIMIT 1 Is it possible to do that with just one expression? Also there arises a problem when I have not two but e.g. three or more search parameters. Is there a generic solution for that? Of course it would come in handy when the search result is

I need to create a ranking of similar strings in a table. I have the following table create table names ( name character varying(255) ); Currently, I'm using pg_trgm module which offers the similarity function, but I have an efficiency problem. I created an index like the Postgres manual suggests : CREATE INDEX trgm_idx ON names USING gist (name gist_trgm_ops); and I'm executing the following query: select (similarity(n1.name, n2.name)) as sim, n1.name, n2.name from names n1, names n2 where n1.name != n2.name and similarity(n1.name, n2.name) > .8 order by sim desc; The query works, but is