pgpartman), opting instead to just add a small background job to our existing worker framework. We added our first partitioned table recently, and things have gotten so good that we skipped bringing in a partition-managing extension (e.g. It’s largely been a story of getting partitioned tables up to feature parity with non-partitioned tables, and they’re now very, very close. Postgres 14: Partitions can be detached in a non-blocking way with ALTER TABLE.Postgres 13: Logical replication on partitioned tables (previously, partitions would have to be replicated individually).Postgres 13: Support for row-level BEFORE triggers on partitioned tables. Postgres 12: Improved INSERT performance, ALTER TABLE ATTACH PARTITION no longer blocks queries.Postgres 12: Foreign keys can reference partitioned tables.Postgres 11: UPDATE statements can move rows between partitions.Postgres 11: INSERT on the parent partitioned table routes rows to their appropriate partition.Postgres 11: Support for PRIMARY KEY, FOREIGN KEY, indexes, and triggers on partitioned tables.Postgres 10: Brings in the original CREATE TABLE.Here’s a sprinkling of new features that have come into Postgres over the last five years: And even once Postgres got support for native partitioning, things were always harder – routing inserts/updates, adding/removing partitions, adding indexes, support for features like foreign keys and triggers, etc.īut, a lot of work has gone into improving the operator experience since partitioning was introduced. Not long ago there was no formal partitioning at all in Postgres – it was entirely a user-level construct which needed all kinds of manual plumbing to run. It executes instantly, and with negligible costs (partitioning has other benefits too). Each row removal land in the WAL, resulting in significant amplification.īut with partitions, deletion becomes a simple DROP TABLE. A long running query must iterate through and mark each one as dead, and even then nothing is reclaimed until an equally expensive vacuum runs through and frees space, and only when it’s allowed to after rows are no longer visible to any other query in the system, whether they’re making use of the large table or not. In Postgres, trying to remove old rows from a large, hot table is flitting with disaster. Hopefully if you followed those steps, your table should be sorted in exactly the order you want.Partitioned tables aren’t an everyday go to, but are invaluable in some cases, particularly when you have a high volume table that’s expected to keep growing. Now unless you want to keep the view, rule, and sequence around, you can drop them:.UPDATE view_team SET priority = nextval('team_priority_seq') This will update each row in sequence, and serves as an alternative to using user-defined variables, as we did in MySQL: You can change more than one field in this rule by adding more fields to the UPDATE part of that query, but since we are only applying changes to the priority field, this will suffice. This specifies that when you try to run an update on the view_team view, it will apply those changes to the team table where we want those changes to show up. To run the update on the view you just created, you have to create a rule telling the view how to interpret UPDATE queries you’re going to run on it:ĬREATE RULE rule_team AS ON UPDATE TO view_team DO INSTEAD UPDATE team SET priority = NEW.priority WHERE id = NEW.id.You must first create a view on the table that you want to update in the particular order that you want to update by:ĬREATE VIEW view_team AS SELECT * FROM team ORDER BY name ASC.It turns out, the solution requires the use of views, rules, and sequences, things that are foreign to most MySQL users and all but the more advanced PostgreSQL users. However, under PostgreSQL, this is much more challenging, and I couldn’t find any easy solution on the web. Piece of cake: each employee is given a certain priority according to name. SET team SET priority = ORDER BY name ASC However, recently they asked us to sort their employee table according to name. This allowed them to order their employees according to any criteria they desire (say, in this case, seniority, or rank). For one particular client, they wanted the ability to sort their list of team members according to priority. In many of our tables we allow site administrators to sort elements (rows) according to a certain priority (in this case, 1 being the highest priority). Something I’ve found frequently valuable is the ability to update a table in a particular order, such as when you want a column to have a particular numerical sequence, and you want that sequence to share the same order as another field. MySQL is great in that it really lets you get away with a lot.
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