Re: Optimize update query - Mailing list pgsql-performance

Thanks for all the great help and advice already! Let me just clear some things, to make my question a little easier to answer :-)

Now my site is a search engine for used cars - not just a car shop with a few hundred cars.

The update query you look at, is an update that is executed once a day in chunks for all active adverts, so we know they are still for sale (one car can be advertised at several places hence several "adverts"). So it's not a "constant stream" but it has a fairly high volume especially at night time though.

A compressed version of my .conf looks like this (note: there is some tweaks at the end of the file)

# All the log stuff is mainly temporary requirement for pgBadger

# The database has been tuned with pgtuner

This shows me, that the by far most time-consuming queries are updates (in general). On avg. a query like the one I showed you, take 1,3 sec (but often it takes several minutes - which makes me wonder). So correct me if I'm wrong here: my theory is, that I have too many too slow update queries, that then often end up in a situation, where they "wait" for each other to finish, hence the sometimes VERY long execution times. So my basic idea here is, that if I could reduce the cost of the updates, then I could get a hight throughput overall.

Here is a sample of the pgBadger analysis:

Queries that took up the most time (N) ^
Rank Total duration Times executed Av. duration (s) Query
1 1d15h28m38.71s
948,711
0.15s
COMMIT;

2 1d2h17m55.43s
401,002
0.24s
INSERT INTO "car_images" ( "car_id", "created_at", "image", "updated_at" ) VALUES ( '', '', '', '' ) returning "id";

3 23h18m33.68s
195,093
0.43s
SELECT DISTINCT "cars".id FROM "cars" LEFT OUTER JOIN "adverts" ON "adverts"."car_id" = "cars"."id" LEFT OUTERJOIN "sellers" ON "sellers"."id" = "adverts"."seller_id" WHERE "cars"."sales_state" = '' AND "cars"."year" = 0 AND"cars"."engine_size" = 0.0 AND ( ( "cars"."id" IS NOT NULL AND "cars"."brand" = '' AND "cars"."model_name" = ''AND "cars"."fuel" = '' AND "cars"."km" = 0 AND "cars"."price" = 0 AND "sellers"."kind" = '' ) ) LIMIT 0;

4 22h45m26.52s
3,374,133
0.02s
SELECT "adverts".* FROM "adverts" WHERE ( source_name = '' AND md5 ( url ) = md5 ( '' ) ) LIMIT 0;

5 10h31m37.18s
29,671
1.28s
UPDATE "adverts" SET "last_observed_at" = '', "data_source_id" = '' WHERE "adverts"."id" IN ( ... ) ;

6 7h18m40.65s
396,393
0.07s
UPDATE "cars" SET "updated_at" = '' WHERE "cars"."id" = 0;

7 7h6m7.87s
241,294
0.11s
UPDATE "cars" SET "images_count" = COALESCE ( "images_count", 0 ) + 0 WHERE "cars"."id" = 0;

8 6h56m11.78s
84,571
0.30s
INSERT INTO "failed_adverts" ( "active_record_object_class", "advert_candidate", "created_at", "exception_class","exception_message", "from_rescraper", "last_retried_at", "retry_count", "source_name", "stack_trace","updated_at", "url" ) VALUES ( NULL, '', '', '', '', NULL, NULL, '', '', '', '', '' ) returning "id";

9 5h47m25.45s
188,402
0.11s
INSERT INTO "adverts" ( "availability_state", "car_id", "created_at", "data_source_id", "deactivated_at","first_extraction", "last_observed_at", "price", "seller_id", "source_id", "source_name", "updated_at", "url" )VALUES ( '', '', '', '', NULL, '', '', '', '', '', '', '', '' ) returning "id";

10 3h4m26.86s
166,235
0.07s
UPDATE "adverts" SET "deactivated_at" = '', "availability_state" = '', "updated_at" = '' WHERE "adverts"."id" = 0;