Horton

Re: HOT chain validation in verify_heapam()

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@lists.postgresql.org, Himanshu Upadhyaya <upadhyaya.himanshu@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Aleksander Alekseev <aleksander@timescale.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2022-11-21T22:06:32Z
Lists: pgsql-hackers 
On Mon, Nov 21, 2022 at 1:34 PM Andres Freund <andres@anarazel.de> wrote:
> Hm. But to get to that point we already need to have decided that xmax
> is not a normal xid. Unhelpfully we reuse the 'xid' variable for xmax as
> well:
>         xid = HeapTupleHeaderGetRawXmax(tuple);
>
> I don't really know the HEAP_XMAX_INVALID branch is trying to do. For
> one, xid already is set to HeapTupleHeaderGetRawXmax(), why is it
> refetching the value?

Right, that detail is correct, but still weird. And suggests that it
might not have been super well thought through.

> So it looks to me like this path should just test !TransactionIdIsValid(xid)?

Agreed. Plus there should be a comment that reminds you that this is a
normal regular transaction ID (easy to miss, because the initial "if"
block for Multis is rather large).

I will push something like that soon.

-- 
Peter Geoghegan

Commits

  1. amcheck: Generalize one of the recently-added update chain checks.

  2. amcheck: Tighten up validation of redirect line pointers.

  3. amcheck: Fix verify_heapam for tuples where xmin or xmax is 0.

  4. amcheck: Fix a few bugs in new update chain validation.

  5. Fix new test case to work on (some?) big-endian architectures.

  6. Don't test HEAP_XMAX_INVALID when freezing xmax.