On 2020-Aug-12, Alvaro Herrera wrote:
> 'anyvisible' mode is not required AFAICS; reading the code, I think this
> could also hit REINDEX CONCURRENTLY and CREATE INDEX CONCURRENTLY, which
> do not use that flag. I didn't try to reproduce it there, though.
> Anyway, I'm going to remove that Assert() I added.
So this is what I propose as the final form of the fix.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From e0abe5d957155285980a40fb33c192100699e8c0 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Wed, 12 Aug 2020 14:02:58 -0400
Subject: [PATCH v4] fix HOT tuples while scanning for index builds
---
src/backend/access/heap/heapam_handler.c | 20 ++++++++++++++++++++
src/backend/access/heap/pruneheap.c | 5 +++--
2 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index 267a6ee25a..ba44e30035 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -1324,6 +1324,12 @@ heapam_index_build_range_scan(Relation heapRelation,
* buffer continuously while visiting the page, so no pruning
* operation can occur either.
*
+ * In cases with only ShareUpdateExclusiveLock on the table, it's
+ * possible for some HOT tuples to appear that we didn't know about
+ * when we first read the page. To handle that case, we re-obtain the
+ * list of root offsets when a HOT tuple points to a root item that we
+ * don't know about.
+ *
* Also, although our opinions about tuple liveness could change while
* we scan the page (due to concurrent transaction commits/aborts),
* the chain root locations won't, so this info doesn't need to be
@@ -1625,6 +1631,20 @@ heapam_index_build_range_scan(Relation heapRelation,
offnum = ItemPointerGetOffsetNumber(&heapTuple->t_self);
+ /*
+ * If a HOT tuple points to a root that we don't know
+ * about, obtain root items afresh. If that still fails,
+ * report it as corruption.
+ */
+ if (root_offsets[offnum - 1] == InvalidOffsetNumber)
+ {
+ Page page = BufferGetPage(hscan->rs_cbuf);
+
+ LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
+ heap_get_root_tuples(page, root_offsets);
+ LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+ }
+
if (!OffsetNumberIsValid(root_offsets[offnum - 1]))
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c
index 256df4de10..7e3d44dfd6 100644
--- a/src/backend/access/heap/pruneheap.c
+++ b/src/backend/access/heap/pruneheap.c
@@ -732,7 +732,7 @@ heap_page_prune_execute(Buffer buffer,
* root_offsets[k - 1] = j.
*
* The passed-in root_offsets array must have MaxHeapTuplesPerPage entries.
- * We zero out all unused entries.
+ * Unused entries are filled with InvalidOffsetNumber (zero).
*
* The function must be called with at least share lock on the buffer, to
* prevent concurrent prune operations.
@@ -747,7 +747,8 @@ heap_get_root_tuples(Page page, OffsetNumber *root_offsets)
OffsetNumber offnum,
maxoff;
- MemSet(root_offsets, 0, MaxHeapTuplesPerPage * sizeof(OffsetNumber));
+ MemSet(root_offsets, InvalidOffsetNumber,
+ MaxHeapTuplesPerPage * sizeof(OffsetNumber));
maxoff = PageGetMaxOffsetNumber(page);
for (offnum = FirstOffsetNumber; offnum <= maxoff; offnum = OffsetNumberNext(offnum))
--
2.20.1
