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	Thu, 9 Sep 2021 10:25:27 -0400
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Christoph Berg <christoph.berg@credativ.de>
cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: trap instead of error on 32 TiB table
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Comments: In-reply-to Christoph Berg <christoph.berg@credativ.de>
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Christoph Berg <christoph.berg@credativ.de> writes:
>> Can you provide a stack trace from that?

> #2  0x0000558b6223d46e in ExceptionalCondition (conditionName=3Dconditio=
nName@entry=3D0x558b623b2577 "tagPtr->blockNum !=3D P_NEW",
>     errorType=3DerrorType@entry=3D0x558b6229b016 "FailedAssertion",
>     fileName=3DfileName@entry=3D0x558b623b2598 "./build/../src/backend/s=
torage/buffer/buf_table.c", lineNumber=3DlineNumber@entry=3D125)
>     at ./build/../src/backend/utils/error/assert.c:67
> #3  0x0000558b620bafb9 in BufTableInsert (tagPtr=3DtagPtr@entry=3D0x7ffe=
c8919330, hashcode=3Dhashcode@entry=3D960067002, buf_id=3D<optimized out>)
>     at ./build/../src/backend/storage/buffer/buf_table.c:125
> #4  0x0000558b620bf827 in BufferAlloc (foundPtr=3D0x7ffec891932b, strate=
gy=3D0x0, blockNum=3D4294967295, forkNum=3DMAIN_FORKNUM,
>     relpersistence=3D112 'p', smgr=3D0x558b62ed4b38) at ./build/../src/b=
ackend/storage/buffer/bufmgr.c:1234

Ah, thanks.  I don't think it's unreasonable for BufTableInsert to contain
that assertion --- we shouldn't be trying to allocate a buffer for an
illegal block number.

The regular error comes from mdextend, but that is too late under this
worldview, because smgrextend expects to be given a zero-filled buffer
to write out.  I think where we ought to be making the check is right
where ReadBuffer_common replaces P_NEW:

    /* Substitute proper block number if caller asked for P_NEW */
    if (isExtend)
+   {
        blockNum =3D smgrnblocks(smgr, forkNum);
+       if (blockNum =3D=3D InvalidBlockNumber)
+            ereport(ERROR,
+                    (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+                     errmsg("cannot extend file \"%s\" beyond %u blocks",
+                            relpath(smgr->smgr_rnode, forkNum),
+                            InvalidBlockNumber)));
+   }

Having done that, the check in md.c could be reduced to an Assert,
although there's something to be said for leaving it as-is as an
extra layer of defense.

			regards, tom lane