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Message-ID: <52d064b8-63bd-45df-a405-b6017d49b300@gmail.com>
Date: Fri, 13 Mar 2026 10:00:00 +0200
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User-Agent: Mozilla Thunderbird
Subject: Re: Buffer locking is special (hints, checksums, AIO writes)
To: Andres Freund <andres@anarazel.de>, Noah Misch <noah@leadboat.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>,
 Melanie Plageman <melanieplageman@gmail.com>,
 Kirill Reshke <reshkekirill@gmail.com>,
 Matthias van de Meent <boekewurm+postgres@gmail.com>,
 pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>,
 Robert Haas <robertmhaas@gmail.com>,
 Michael Paquier <michael.paquier@gmail.com>
References: <5dwlfu2jyzkyf3nrlzxxblxctb6xio5es73ptgsahjnmfu5miu@772rc764hfhi>
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 <CALdSSPgyc7VuMLUZ8J7v2G-PebBa_vEi+mp-cLkcOwNycB56Hw@mail.gmail.com>
 <kjdgvws34gpnz4y6xu5aaeul5mspgy3ahvyiw4lndb3ecsacdb@b2ccyowotpqh>
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 <68e89de8-5f6c-4eaf-a800-e16a5e487667@iki.fi>
 <20260215195239.ce.noahmisch@microsoft.com>
 <mheeefrtikvgjnjsenocvo3afj7vlpr5rljkzevssxs77n2zdt@sugqtjhryydo>
Content-Language: en-US
From: Alexander Lakhin <exclusion@gmail.com>
In-Reply-To: <mheeefrtikvgjnjsenocvo3afj7vlpr5rljkzevssxs77n2zdt@sugqtjhryydo>
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Hello Andres,

12.03.2026 00:40, Andres Freund wrote:
> I pushed this and many of the later patches in the series.  Here are updated
> versions of the remaining changes.  The last two previously were one commit
> with "WIP" in the title. The first one has, I think, not had a lot of review -
> but it's also not a complicated change.

I've discovered that starting from 82467f627, the following query:
SET cpu_operator_cost = 1000;
CREATE TABLE t (i INT);
INSERT INTO T SELECT 1 FROM generate_series(1, 1000) a;
CREATE INDEX hi on t USING HASH (i);
DELETE FROM t WHERE i = 1;
DELETE FROM t WHERE i = 1;

triggers
TRAP: failed Assert("BufferIsValid(buffer)"), File: "bufmgr.c", Line: 497, PID: 3942058

#4  0x000079a60ae288ff in __GI_abort () at ./stdlib/abort.c:79
#5  0x00005a68d9343eef in ExceptionalCondition (conditionName=conditionName@entry=0x5a68d93ac27d "BufferIsValid(buffer)",
     fileName=fileName@entry=0x5a68d93c99ef "bufmgr.c", lineNumber=lineNumber@entry=497) at assert.c:65
#6  0x00005a68d91a18eb in GetPrivateRefCountEntry (do_move=true, buffer=<optimized out>) at bufmgr.c:497
#7  SharedBufferBeginSetHintBits (lockstate=<synthetic pointer>, buf_hdr=0x79e5febbbc40, buffer=<optimized out>)
     at bufmgr.c:6830
#8  BufferBeginSetHintBits (buffer=<optimized out>) at bufmgr.c:6931
#9  0x00005a68d8e3c862 in _hash_kill_items (scan=<optimized out>) at hashutil.c:603
#10 0x00005a68d8e3b7c3 in _hash_next (scan=0x5a68e735f938, dir=<optimized out>) at hashsearch.c:69
#11 0x00005a68d8e616ce in index_getnext_tid (scan=scan@entry=0x5a68e735f938, direction=direction@entry=ForwardScanDirection)
     at indexam.c:647
...
#25 0x00005a68d91eb4ad in exec_simple_query (query_string=0x5a68e7270120 "DELETE FROM t WHERE i = 1;") at postgres.c:1277
...

Could you please look at this?

Best regards,
Alexander
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    <div class="moz-cite-prefix">Hello Andres,<br>
      <br>
      12.03.2026 00:40, Andres Freund wrote:<span
      style="white-space: pre-wrap">
</span></div>
    <blockquote type="cite"
cite="mid:mheeefrtikvgjnjsenocvo3afj7vlpr5rljkzevssxs77n2zdt@sugqtjhryydo">
      <pre wrap="" class="moz-quote-pre">I pushed this and many of the later patches in the series.  Here are updated
versions of the remaining changes.  The last two previously were one commit
with "WIP" in the title. The first one has, I think, not had a lot of review -
but it's also not a complicated change.
</pre>
    </blockquote>
    <br>
    I've discovered that starting from 82467f627, the following query:<br>
    SET cpu_operator_cost = 1000;<br>
    CREATE TABLE t (i INT);<br>
    INSERT INTO T SELECT 1 FROM generate_series(1, 1000) a;<br>
    CREATE INDEX hi on t USING HASH (i);<br>
    DELETE FROM t WHERE i = 1;<br>
    DELETE FROM t WHERE i = 1;<br>
    <br>
    triggers<br>
    TRAP: failed Assert("BufferIsValid(buffer)"), File: "bufmgr.c",
    Line: 497, PID: 3942058<br>
    <br>
    #4  0x000079a60ae288ff in __GI_abort () at ./stdlib/abort.c:79<br>
    #5  0x00005a68d9343eef in ExceptionalCondition
    (conditionName=conditionName@entry=0x5a68d93ac27d
    "BufferIsValid(buffer)", <br>
        fileName=fileName@entry=0x5a68d93c99ef "bufmgr.c",
    lineNumber=lineNumber@entry=497) at assert.c:65<br>
    #6  0x00005a68d91a18eb in GetPrivateRefCountEntry (do_move=true,
    buffer=&lt;optimized out&gt;) at bufmgr.c:497<br>
    #7  SharedBufferBeginSetHintBits (lockstate=&lt;synthetic
    pointer&gt;, buf_hdr=0x79e5febbbc40, buffer=&lt;optimized out&gt;)<br>
        at bufmgr.c:6830<br>
    #8  BufferBeginSetHintBits (buffer=&lt;optimized out&gt;) at
    bufmgr.c:6931<br>
    #9  0x00005a68d8e3c862 in _hash_kill_items (scan=&lt;optimized
    out&gt;) at hashutil.c:603<br>
    #10 0x00005a68d8e3b7c3 in _hash_next (scan=0x5a68e735f938,
    dir=&lt;optimized out&gt;) at hashsearch.c:69<br>
    #11 0x00005a68d8e616ce in index_getnext_tid
    (scan=scan@entry=0x5a68e735f938,
    direction=direction@entry=ForwardScanDirection)<br>
        at indexam.c:647<br>
    ...<br>
    #25 0x00005a68d91eb4ad in exec_simple_query
    (query_string=0x5a68e7270120 "DELETE FROM t WHERE i = 1;") at
    postgres.c:1277<br>
    ...<br>
    <br>
    Could you please look at this?<br>
    <br>
    Best regards,<br>
    Alexander<br>
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