Re: releasing ParallelApplyTxnHash when pa_launch_parallel_worker returns NULL

On Tue, Jan 10, 2023 at 6:13 PM houzj(dot)fnst(at)fujitsu(dot)com <
houzj(dot)fnst(at)fujitsu(dot)com> wrote:

> On Wednesday, January 11, 2023 1:25 AM Ted Yu <yuzhihong(at)gmail(dot)com> wrote:
>
> > I was reading src/backend/replication/logical/applyparallelworker.c .
> > In `pa_allocate_worker`, when pa_launch_parallel_worker returns NULL, I
> think the `ParallelApplyTxnHash` should be released.
>
> Thanks for reporting.
>
> ParallelApplyTxnHash is used to cache the state of streaming transactions
> being
> applied. There could be multiple streaming transactions being applied in
> parallel and their information were already saved in ParallelApplyTxnHash,
> so
> we should not release them just because we don't have a worker available to
> handle a new transaction here.
>
> Best Regards,
> Hou zj
>
Hi,

/* First time through, initialize parallel apply worker state
hashtable. */
if (!ParallelApplyTxnHash)

I think it would be better if `ParallelApplyTxnHash` is created by the
first successful parallel apply worker.

Please take a look at the new patch and see if it makes sense.

Cheers