> On Mar 4, 2026, at 16:59, Chao Li <[email protected]> wrote:
>
>
>
>> On Mar 3, 2026, at 23:52, Melanie Plageman <[email protected]> wrote:
>>
>>
>>> Otherwise, if prstate->pagefrz.FreezePageConflictXid is still possibly be
>>> InvalidTransactionId, then the Assert should be changed to something like:
>>>
>>> Assert(prstate->pagefrz.FreezePageConflictXid == InvalidTransactionId ||
>>> TransactionIdPrecedesOrEquals(prstate->pagefrz.FreezePageConflictXid,
>>> prstate->cutoffs->OldestXmin)
>>
>> This is covered by TransactionIdPrecedesOrEquals because
>> InvalidTransactionId is 0. We assume that in many places throughout
>> the code.
>>
>
> I understood that TransactionIdPrecedesOrEquals(InvalidTransactionId,
> prstate->cutoffs->OldestXmin) is true, but that would leave an impression to
> code readers that prstate->pagefrz.FreezePageConflictXid could not be
> InvalidTransactionId. Thus I think my version explicitly tells that
> prstate->pagefrz.FreezePageConflictXid could be InvalidTransactionId at the
> point.
>
>
>>> I will continue with 0005 tomorrow.
>>
>
> 4 - 0005
> ```
> * Caller must have pin on the buffer, and must *not* have a lock on it.
> */
> void
> -heap_page_prune_opt(Relation relation, Buffer buffer)
> +heap_page_prune_opt(Relation relation, Buffer buffer, Buffer *vmbuffer)
> ```
>
> I don’t see why vmbuffer has to be of pointer type. Buffer type is underlying
> int, I checked the last commit, vmbuffer only passes in data into the
> function without passing out anything.
>
> As we add the new parameter vmbuffer, though it’s not used in this commit, I
> think it’d be better to update the header commit to explain what this
> parameter will do.
>
> 5 - 0006
> ```
> + *
> + * heap_fix_vm_corruption() makes changes to the VM and, potentially, the
> heap
> + * page, but it does not need to be done in a critical section because
> + * clearing the VM is not WAL-logged.
> + */
> +static void
> +heap_fix_vm_corruption(PruneState *prstate, OffsetNumber offnum)
> ```
>
> Nit: why the last paragraph of the header comments uses the function name
> instead of “this function”? Looks like a copy-pasto.
>
> 6 - 0006
> ```
> + if (prstate->lpdead_items > 0)
> + {
> + ereport(WARNING,
> + (errcode(ERRCODE_DATA_CORRUPTED),
> + errmsg("LP_DEAD item found on page marked as all-visible"),
> + errdetail("relation \"%s\", page %u, tuple %u",
> + RelationGetRelationName(prstate->relation),
> + prstate->block, offnum)));
> + }
> + else
> + {
> + ereport(WARNING,
> + (errcode(ERRCODE_DATA_CORRUPTED),
> + errmsg("tuple not visible to all found on page marked as all-visible"),
> + errdetail("relation \"%s\", page %u, tuple %u",
> + RelationGetRelationName(prstate->relation),
> + prstate->block, offnum)));
> + }
> ```
>
> I recently just learned that a detail message should use complete sentences,
> and end each with a period, and capitalize the first word of sentences. See
> https://www.postgresql.org/docs/current/error-style-guide.html.
>
> 7 - 0006
> ```
> + else if (prstate->vmbits & VISIBILITYMAP_VALID_BITS)
> + {
> + /*
> + * As of PostgreSQL 9.2, the visibility map bit should never be set if
> + * the page-level bit is clear. However, it's possible that the bit
> + * got cleared after heap_vac_scan_next_block() was called, so we must
> + * recheck with buffer lock before concluding that the VM is corrupt.
> + */
> + ereport(WARNING,
> + (errcode(ERRCODE_DATA_CORRUPTED),
> + errmsg("page %u in \"%s\" is not marked all-visible but visibility map bit
> is set",
> + prstate->block,
> + RelationGetRelationName(prstate->relation))));
> + }
> ```
>
> The comment says “we must recheck with buffer lock before…”, but it only log
> a warning message. Is the comment stale?
>
> 8 - 0007
> ```
> +static void
> +heap_page_bypass_prune_freeze(PruneState *prstate, PruneFreezeResult
> *presult)
> +{
> + OffsetNumber maxoff = PageGetMaxOffsetNumber(prstate->page);
> + Page page = prstate->page;
> +
> + Assert(prstate->vmbits & VISIBILITYMAP_ALL_FROZEN ||
> + (prstate->vmbits & VISIBILITYMAP_ALL_VISIBLE &&
> + !prstate->attempt_freeze));
> +
> + /* We'll fill in presult for the caller */
> + memset(presult, 0, sizeof(PruneFreezeResult));
> +
> + /*
> + * Since the page is all-visible, a count of the normal ItemIds on the
> + * page should be sufficient for vacuum's live tuple count.
> + */
> + for (OffsetNumber off = FirstOffsetNumber;
> + off <= maxoff;
> + off = OffsetNumberNext(off))
> + {
> + if (ItemIdIsNormal(PageGetItemId(page, off)))
> + prstate->live_tuples++;
> + }
> +
> + presult->live_tuples = prstate->live_tuples;
> +
> + /* Clear any stale prune hint */
> + if (TransactionIdIsValid(PageGetPruneXid(page)))
> + {
> + PageClearPrunable(page);
> + MarkBufferDirtyHint(prstate->buffer, true);
> + }
> +
> + presult->vmbits = prstate->vmbits;
> +
> + if (!PageIsEmpty(page))
> + presult->hastup = true;
> +}
> ```
>
> * Given this function has done PageIsEmpty(page), that that is true, we don’t
> need to count live_tuples, right? That could be a tiny optimization.
> * I see heap_page_bypass_prune_freeze() is only called in one place and
> immediately after prune_freeze_setup() and heap_fix_vm_corruption(), so
> prstate->vmbits must be 0, so do we need to do presult->vmbits =
> prstate->vmbits;?
> * Do we need to set all_visible and all_frozen to presult?
>
> 0008 LGTM
>
> I will continue with 0009 tomorrow.
>
9 - 0009
···
+ * Currently, only VACUUM performs freezing, but other callers may in
the
+ * future. Other callers must initialize prstate.all_frozen to false,
···
Nit: prstate.all_frozen -> prstate.set_all_frozen
I saw you have fixed this in 0010, but I think it’s better also fix it here.
10 - 0010
```
+ * Whether or not the page was newly set all-visible and all-frozen
during
+ * phase I of vacuuming.
*/
- uint8 vmbits;
+ BlockNumber new_all_visible_pages;
+ BlockNumber new_all_visible_frozen_pages;
+ BlockNumber new_all_frozen_pages;
```
These 3 fields are actually counts rather than pointers to blocks, using type
BlockNumber are quite confusing, though underlying BlockNumber is uint32. I
think they can be just int type.
11 - 0010
```
+ BlockNumber new_all_visible_pages;
+ BlockNumber new_all_visible_frozen_pages;
+ BlockNumber new_all_frozen_pages;
```
I don’t see where these 3 fields are initialized. In lazy_scan_prune(), presult
is defined as:
```
PruneFreezeResult presult;
```
So, those fields will hold random values.
12 - 0010
```
+ * conflict would ahve been handled in reaction to the WAL record
freezing
```
Nit: ahve -> have
0011 LGTM
13 - 0012 - bufmask.c
```
+ * we don't mark the page all-visible. See heap_xlog_prune_and_freeze()
+ * for more details.
```
I don’t find a function named heap_xlog_prune_and_freeze().
14 - 0012 - heapam_xlog.c
```
+ * same approach is taken when replaying XLOG_HEAP2_PRUNE* records (see
+ * heap_xlog_prune_and_freeze()).
```
Same as 13.
0013 LGTM
I will try to finish the rest 5 commits tomorrow.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
