From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
---|---|
To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
Cc: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Andres Freund <andres(at)anarazel(dot)de>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com> |
Subject: | Re: BitmapHeapScan streaming read user and prelim refactoring |
Date: | 2024-03-31 15:45:51 |
Message-ID: | 20240331154551.lty4mundyoyhtixw@liskov |
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Lists: | pgsql-hackers |
On Fri, Mar 29, 2024 at 12:05:15PM +0100, Tomas Vondra wrote:
>
>
> On 3/29/24 02:12, Thomas Munro wrote:
> > On Fri, Mar 29, 2024 at 10:43 AM Tomas Vondra
> > <tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
> >> I think there's some sort of bug, triggering this assert in heapam
> >>
> >> Assert(BufferGetBlockNumber(hscan->rs_cbuf) == tbmres->blockno);
> >
> > Thanks for the repro. I can't seem to reproduce it (still trying) but
> > I assume this is with Melanie's v11 patch set which had
> > v11-0016-v10-Read-Stream-API.patch.
> >
> > Would you mind removing that commit and instead applying the v13
> > stream_read.c patches[1]? v10 stream_read.c was a little confused
> > about random I/O combining, which I fixed with a small adjustment to
> > the conditions for the "if" statement right at the end of
> > read_stream_look_ahead(). Sorry about that. The fixed version, with
> > eic=4, with your test query using WHERE a < a, ends its scan with:
> >
>
> I'll give that a try. Unfortunately unfortunately the v11 still has the
> problem I reported about a week ago:
>
> ERROR: prefetch and main iterators are out of sync
>
> So I can't run the full benchmarks :-( but master vs. streaming read API
> should work, I think.
Odd, I didn't notice you reporting this ERROR popping up. Now that I
take a look, v11 (at least, maybe also v10) had this very sill mistake:
if (scan->bm_parallel == NULL &&
scan->rs_pf_bhs_iterator &&
hscan->pfblockno > hscan->rs_base.blockno)
elog(ERROR, "prefetch and main iterators are out of sync");
It errors out if the prefetch block is ahead of the current block --
which is the opposite of what we want. I've fixed this in attached v12.
This version also has v13 of the streaming read API. I noticed one
mistake in my bitmapheap scan streaming read user -- it freed the
streaming read object at the wrong time. I don't know if this was
causing any other issues, but it at least is fixed in this version.
- Melanie
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