> 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.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
