From: | Fabrízio de Royes Mello <fabriziomello(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>, Mats Kindahl <mats(at)timescale(dot)com> |
Subject: | Re: Is SPI + Procedures (with COMMIT) inside a bgworker broken? |
Date: | 2021-09-13 23:31:34 |
Message-ID: | CAFcNs+pTiqVbPJD0Vywfb4H7LA7FKaemcWYce8sCcjH9AWKxNQ@mail.gmail.com |
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On Mon, Sep 13, 2021 at 4:30 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> The direct cause of that is that SPI_execute() doesn't permit the called
> query to perform COMMIT/ROLLBACK, which is because most callers would fail
> to cope with that. You can instruct SPI to allow that by replacing the
> SPI_execute() call with something like
>
> SPIExecuteOptions options;
>
> ...
> memset(&options, 0, sizeof(options));
> options.allow_nonatomic = true;
>
> ret = SPI_execute_extended(buf.data, &options);
>
I completely forgot about the SPI execute options... Thanks for the
explanation!!!
> However, that's not enough to make this example work :-(.
> I find that it still fails inside the procedure's COMMIT,
> with
>
> 2021-09-13 15:14:54.775 EDT worker_spi[476310] ERROR: portal snapshots
(0) did not account for all active snapshots (1)
> 2021-09-13 15:14:54.775 EDT worker_spi[476310] CONTEXT: PL/pgSQL
function schema4.counted_proc() line 1 at COMMIT
> SQL statement "CALL "schema4"."counted_proc"()"
>
> I think what this indicates is that worker_spi_main's cavalier
> management of the active snapshot isn't up to snuff for this
> use-case. The error is coming from ForgetPortalSnapshots, which
> is expecting that all active snapshots are attached to Portals;
> but that one isn't.
>
That is exactly the root cause of all my investigation.
At Timescale we have a scheduler (background worker) that launches another
background worker to "execute a job", and by executing a job it means to
call a function [1] or a procedure [2] directly without a SPI.
But now a user raised an issue about snapshots [3] and when I saw the code
for the first time I tried to use SPI and it didn't work as expected.
Even tweaking worker_spi to execute the procedure without SPI by calling
ExecuteCallStmt (attached) we end up with the same situation about the
active snapshots:
2021-09-13 20:14:36.654 -03 [21483] LOG: worker_spi worker 2 initialized
with schema2.counted
2021-09-13 20:14:36.655 -03 [21484] LOG: worker_spi worker 1 initialized
with schema1.counted
2021-09-13 20:14:36.657 -03 [21483] ERROR: portal snapshots (0) did not
account for all active snapshots (1)
2021-09-13 20:14:36.657 -03 [21483] CONTEXT: PL/pgSQL function
schema2.counted_proc() line 1 at COMMIT
2021-09-13 20:14:36.657 -03 [21484] ERROR: portal snapshots (0) did not
account for all active snapshots (1)
2021-09-13 20:14:36.657 -03 [21484] CONTEXT: PL/pgSQL function
schema1.counted_proc() line 1 at COMMIT
2021-09-13 20:14:36.659 -03 [21476] LOG: background worker "worker_spi"
(PID 21483) exited with exit code 1
2021-09-13 20:14:36.659 -03 [21476] LOG: background worker "worker_spi"
(PID 21484) exited with exit code 1
> Probably the most appropriate fix is to make worker_spi_main
> set up a Portal to run the query inside of. There are other
> bits of code that are not happy if they're not inside a Portal,
> so if you're hoping to run arbitrary SQL this way, sooner or
> later you're going to have to cross that bridge.
>
I started digging with it [4] by creating a Portal from scratch to execute
the Function or Procedure and it worked.
We're wondering if we can avoid the parser for PortalRun, can we??
Regards,
[1]
https://github.com/timescale/timescaledb/blob/master/tsl/src/bgw_policy/job.c#L726
[2]
https://github.com/timescale/timescaledb/blob/master/tsl/src/bgw_policy/job.c#L741
[3] https://github.com/timescale/timescaledb/issues/3545
[4]
https://github.com/fabriziomello/timescaledb/blob/issue/3545/tsl/src/bgw_policy/job.c#L824
--
Fabrízio de Royes Mello
Attachment | Content-Type | Size |
---|---|---|
worker_spi_executecallstmt.patch | text/x-patch | 5.0 KB |
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