Horton

Re: HOT chain validation in verify_heapam()

Aleksander Alekseev <aleksander@timescale.com>

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From: Aleksander Alekseev <aleksander@timescale.com>
To: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Cc: Himanshu Upadhyaya <upadhyaya.himanshu@gmail.com>, Robert Haas <robertmhaas@gmail.com>
Date: 2022-09-19T14:57:36Z
Lists: pgsql-hackers

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Hi Himanshu,

> Done, updated in the v3 patch.

Thanks for the updated patch.

Here is v4 with fixed compiler warnings and some minor tweaks from me.

I didn't put too much thought into the algorithm but I already see
something strange. At verify_heapam.c:553 you declared curr_xmax and
next_xmin. However the variables are not used/initialized until you
do:

```
            if (lp_valid[nextoffnum] && lp_valid[ctx.offnum] &&
                TransactionIdIsValid(curr_xmax) &&
                TransactionIdEquals(curr_xmax, next_xmin)) {
/* ... */
```

In v4 I elected to initialize both curr_xmax and next_xmin with
InvalidTransactionId for safety and in order to silence the compiler
but still there is no way this condition can succeed.

Please make sure there is no logic missing.

-- 
Best regards,
Aleksander Alekseev

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.