Re: Deadlock between concurrent index builds on different tables

On Fri, Dec 22, 2017 at 1:53 PM, Jeremy Finzel <finzelj@gmail.com> wrote:

> I am attempting to build several indexes in parallel, guaranteeing that I
> never build one on the same table twice.  I understand I can't build two on
> the same table at once or I will get a deadlock.  However, I am also
> getting a deadlock when doing several in parallel on different tables.
>
> Here is an example of the error I am getting:
>
> 2017-12-22 15:48:07.669 CST,"CREATE INDEX",2017-12-22 15:48:02
> CST,8/32,0,ERROR,40P01,"deadlock detected","Process 4470 waits for
> ShareLock on virtual transaction 4/262; blocked by process 4466.
> Process 4466 waits for ShareLock on virtual transaction 8/32; blocked by
> process 4470.
> Process 4470: CREATE INDEX CONCURRENTLY index_foo_on_created_at ON foo
> USING btree (created_at);
> Process 4466: CREATE INDEX CONCURRENTLY index_bar_on_id ON bar USING btree
> (id);","See server log for query details.",,,,"CREATE INDEX CONCURRENTLY
> index_foo_on_created_at ON foo USING btree (created_at);",,,""
>
> Here is my process:
>
>    - Kick off one index build and background 1 second apart, using a
>    queue table to determine what indexes to build and what is finished
>    - When I determine if a index can be built, I first check if there is
>    another already in build on target table before starting another
>    - After the index is built in each workflow, I mark it as built in a
>    queue table
>
> I assume that one of the indexes (the earlier transaction) is building and
> taking so long that several finished indexes end up waiting, and there is
> perhaps a limit to that?
>

Each index build needs to wait for all other transactions (Including the
ones used by the other index build) to finish.  So I don't think a deadlock
here is unexpected.

Cheers,

Jeff