CREATE INDEX does not block table reads

[seanpascoe]

Folks at my company have been passing this repo and associated article around like it's gospel, but I'm pretty sure you're wrong on creating postgres indexes and blocking table reads:

Creating an index will block both reads and writes in Postgres.

CREATE INDEX will block table writes but not reads in postgres

With Postgres, instead create the index concurrently which does not block reads.

creating the index concurrently will not block writes.

From the postgresql docs regarding CONCURRENTLY

When this option is used, PostgreSQL will build the index without taking any locks that prevent concurrent inserts, updates, or deletes on the table; whereas a standard index build locks out writes (but not reads) on the table until it's done. There are several caveats to be aware of when using this option — see Building Indexes Concurrently.

[dbernheisel]

Thanks, there's definitely an inconsistency here. The example is correct in stating "which will block writes" but the description says (incorrectly) it will also block reads. This must've been some copy-paste error; sorry about that. I'll get a PR up to resolve.

[dbernheisel]

Also see some notes I left in #8

[seanpascoe]

Thanks, though you still have the language under the "Good", suggesting postgres normally blocks reads without concurrently:

With Postgres, instead create the index concurrently which does not block reads. There are two options:

[dbernheisel]

fixed!