Обсуждение: ORDER BY LIMIT n does not work as described when using partitioned tables
ORDER BY LIMIT n does not work as described when using partitioned tables
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The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/10/indexes-ordering.html Description: Dear Postgres team, First, thanks for an excellent product and great documentation. This is world class. We have found an issue with index and ORDER BY LIMIT 1 when using partitioned tables. The tabled is partitioned using declarative partitioning, the partition is created on timestamptz. There is one partition per day. Looking at the query planner, it is clear that it is trying to open up all the indexes (we have hundreds of partitioned tables) to find the 1 row that we are asking for, even if the row is in the first table that the index should look at. The result is that the query is extremely slow. All the benefits of using partitioned tables seems to be gone, it is worse than not partitioning. I would prefer that the issue is solved in the partitioned table, in this case the documentation is correct. If it is not possible to solve the partitioning issue, then the documentation should be updated. Here are the scripts: CREATE TABLE history.history_bools ( thing_id bigint, boolvalue boolean, "timestamp" timestamp with time zone NOT NULL ) PARTITION BY RANGE ("timestamp") WITH ( OIDS = FALSE ) TABLESPACE pg_default; ALTER TABLE history.history_bools OWNER to postgres; -- Partitions SQL CREATE TABLE history.history_bools_2018_05_01 PARTITION OF history.history_bools FOR VALUES FROM ('2018-04-30 17:00:00-07') TO ('2018-05-01 17:00:00-07'); CREATE UNIQUE INDEX history_bools_2018_05_01_idx ON history.history_bools_2018_05_01 USING btree (thing_id, "timestamp") TABLESPACE pg_default; CREATE TABLE history.history_bools_2018_05_02 PARTITION OF history.history_bools FOR VALUES FROM ('2018-05-01 17:00:00-07') TO ('2018-05-02 17:00:00-07'); CREATE UNIQUE INDEX history_bools_2018_05_02_idx ON history.history_bools_2018_05_02 USING btree (thing_id, "timestamp") TABLESPACE pg_default; .... SELECT * FROM history.history_bools WHERE thing_id = 1 AND "timestamp" < '2018-05-03 12:00:00';