Than you for reviewing!
On Thu, Jul 7, 2016 at 7:06 AM, Andres Freund <[email protected]> wrote:
> On 2016-07-05 23:37:59 +0900, Masahiko Sawada wrote:
>> diff --git a/src/backend/access/heap/heapam.c
>> b/src/backend/access/heap/heapam.c
>> index 57da57a..fd66527 100644
>> --- a/src/backend/access/heap/heapam.c
>> +++ b/src/backend/access/heap/heapam.c
>> @@ -3923,6 +3923,17 @@ l2:
>>
>> if (need_toast || newtupsize > pagefree)
>> {
>> + /*
>> + * To prevent data corruption due to updating old tuple by
>> + * other backends after released buffer
>
> That's not really the reason, is it? The prime problem is crash safety /
> replication. The row-lock we're faking (by setting xmax to our xid),
> prevents concurrent updates until this backend died.
Fixed.
>> , we need to emit that
>> + * xmax of old tuple is set and clear visibility map bits if
>> + * needed before releasing buffer. We can reuse xl_heap_lock
>> + * for this purpose. It should be fine even if we crash midway
>> + * from this section and the actual updating one later, since
>> + * the xmax will appear to come from an aborted xid.
>> + */
>> + START_CRIT_SECTION();
>> +
>> /* Clear obsolete visibility flags ... */
>> oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
>> oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
>> @@ -3936,6 +3947,46 @@ l2:
>> /* temporarily make it look not-updated */
>> oldtup.t_data->t_ctid = oldtup.t_self;
>> already_marked = true;
>> +
>> + /* Clear PD_ALL_VISIBLE flags */
>> + if (PageIsAllVisible(BufferGetPage(buffer)))
>> + {
>> + all_visible_cleared = true;
>> + PageClearAllVisible(BufferGetPage(buffer));
>> + visibilitymap_clear(relation,
>> BufferGetBlockNumber(buffer),
>> + vmbuffer);
>> + }
>> +
>> + MarkBufferDirty(buffer);
>> +
>> + if (RelationNeedsWAL(relation))
>> + {
>> + xl_heap_lock xlrec;
>> + XLogRecPtr recptr;
>> +
>> + /*
>> + * For logical decoding we need combocids to properly
>> decode the
>> + * catalog.
>> + */
>> + if (RelationIsAccessibleInLogicalDecoding(relation))
>> + log_heap_new_cid(relation, &oldtup);
>
> Hm, I don't see that being necessary here. Row locks aren't logically
> decoded, so there's no need to emit this here.
Fixed.
>
>> + /* Clear PD_ALL_VISIBLE flags */
>> + if (PageIsAllVisible(page))
>> + {
>> + Buffer vmbuffer = InvalidBuffer;
>> + BlockNumber block = BufferGetBlockNumber(*buffer);
>> +
>> + all_visible_cleared = true;
>> + PageClearAllVisible(page);
>> + visibilitymap_pin(relation, block, &vmbuffer);
>> + visibilitymap_clear(relation, block, vmbuffer);
>> + }
>> +
>
> That clears all-visible unnecessarily, we only need to clear all-frozen.
>
Fixed.
>
>> @@ -8694,6 +8761,23 @@ heap_xlog_lock(XLogReaderState *record)
>> }
>> HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
>> HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
>> +
>> + /* The visibility map need to be cleared */
>> + if ((xlrec->infobits_set & XLHL_ALL_VISIBLE_CLEARED) != 0)
>> + {
>> + RelFileNode rnode;
>> + Buffer vmbuffer = InvalidBuffer;
>> + BlockNumber blkno;
>> + Relation reln;
>> +
>> + XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
>> + reln = CreateFakeRelcacheEntry(rnode);
>> +
>> + visibilitymap_pin(reln, blkno, &vmbuffer);
>> + visibilitymap_clear(reln, blkno, vmbuffer);
>> + PageClearAllVisible(page);
>> + }
>> +
>
>
>> PageSetLSN(page, lsn);
>> MarkBufferDirty(buffer);
>> }
>> diff --git a/src/include/access/heapam_xlog.h
>> b/src/include/access/heapam_xlog.h
>> index a822d0b..41b3c54 100644
>> --- a/src/include/access/heapam_xlog.h
>> +++ b/src/include/access/heapam_xlog.h
>> @@ -242,6 +242,7 @@ typedef struct xl_heap_cleanup_info
>> #define XLHL_XMAX_EXCL_LOCK 0x04
>> #define XLHL_XMAX_KEYSHR_LOCK 0x08
>> #define XLHL_KEYS_UPDATED 0x10
>> +#define XLHL_ALL_VISIBLE_CLEARED 0x20
>
> Hm. We can't easily do that in the back-patched version; because a
> standby won't know to check for the flag . That's kinda ok, since we
> don't yet need to clear all-visible yet at that point of
> heap_update. But that better means we don't do so on the master either.
>
Attached latest version patch.
I changed visibilitymap_clear function so that it allows to specify
bits being cleared.
The function that needs to clear the only all-frozen bit on visibility
map calls visibilitymap_clear_extended function to clear particular
bit.
Other function can call visibilitymap_clear function to clear all bits
for one page.
Instead of adding XLHL_ALL_VISIBLE_CLEARED, we do vm loop up for back branches.
To reduce unnecessary looking up visibility map, I changed it so that
we check the PD_ALL_VISIBLE on heap page, and then look up all-frozen
bit on visibility map if necessary.
Regards,
--
Masahiko Sawada
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 57da57a..e2efba3 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -3923,6 +3923,16 @@ l2:
if (need_toast || newtupsize > pagefree)
{
+ /*
+ * For crash safety, we need to emit that xmax of old tuple is set
+ * and clear only the all-frozen bit on visibility map if needed
+ * before releasing the buffer. We can reuse xl_heap_lock for this
+ * purpose. It should be fine even if we crash midway from this
+ * section and the actual updating one later, since the xmax will
+ * appear to come from an aborted xid.
+ */
+ START_CRIT_SECTION();
+
/* Clear obsolete visibility flags ... */
oldtup.t_data->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
oldtup.t_data->t_infomask2 &= ~HEAP_KEYS_UPDATED;
@@ -3936,6 +3946,36 @@ l2:
/* temporarily make it look not-updated */
oldtup.t_data->t_ctid = oldtup.t_self;
already_marked = true;
+
+ /* Clear only the all-frozen bit on visibility map if needed */
+ if (PageIsAllVisible(BufferGetPage(buffer)) &&
+ VM_ALL_FROZEN(relation, block, &vmbuffer))
+ {
+ visibilitymap_clear_extended(relation, block, vmbuffer,
+ VISIBILITYMAP_ALL_FROZEN);
+ }
+
+ MarkBufferDirty(buffer);
+
+ if (RelationNeedsWAL(relation))
+ {
+ xl_heap_lock xlrec;
+ XLogRecPtr recptr;
+
+ XLogBeginInsert();
+ XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+
+ xlrec.offnum = ItemPointerGetOffsetNumber(&oldtup.t_self);
+ xlrec.locking_xid = xmax_old_tuple;
+ xlrec.infobits_set = compute_infobits(oldtup.t_data->t_infomask,
+ oldtup.t_data->t_infomask2);
+ XLogRegisterData((char *) &xlrec, SizeOfHeapLock);
+ recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK);
+ PageSetLSN(page, recptr);
+ }
+
+ END_CRIT_SECTION();
+
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
/*
@@ -4506,6 +4546,7 @@ heap_lock_tuple(Relation relation, HeapTuple tuple,
ItemPointer tid = &(tuple->t_self);
ItemId lp;
Page page;
+ Buffer vmbuffer = InvalidBuffer;
TransactionId xid,
xmax;
uint16 old_infomask,
@@ -5034,6 +5075,17 @@ failed:
if (HEAP_XMAX_IS_LOCKED_ONLY(new_infomask))
tuple->t_data->t_ctid = *tid;
+ /* Clear only the all-frozen bit on visibility map if needed */
+ if (PageIsAllVisible(page) &&
+ VM_ALL_FROZEN(relation, BufferGetBlockNumber(*buffer), &vmbuffer))
+ {
+ BlockNumber block = BufferGetBlockNumber(*buffer);
+
+ visibilitymap_pin(relation, block, &vmbuffer);
+ visibilitymap_clear_extended(relation, block, vmbuffer,
+ VISIBILITYMAP_ALL_FROZEN);
+ }
+
MarkBufferDirty(*buffer);
/*
@@ -5072,6 +5124,8 @@ failed:
END_CRIT_SECTION();
LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
+ if (BufferIsValid(vmbuffer))
+ ReleaseBuffer(vmbuffer);
/*
* Don't update the visibility map here. Locking a tuple doesn't change
@@ -8694,6 +8748,22 @@ heap_xlog_lock(XLogReaderState *record)
}
HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
+
+ /* The all-frozen bit on visibility map need to be cleared if needed */
+ if (PageIsAllVisible(BufferGetPage(buffer)))
+ {
+ RelFileNode rnode;
+ Buffer vmbuffer = InvalidBuffer;
+ BlockNumber blkno;
+ Relation reln;
+
+ XLogRecGetBlockTag(record, 0, &rnode, NULL, &blkno);
+ reln = CreateFakeRelcacheEntry(rnode);
+ visibilitymap_clear_extended(reln, blkno, vmbuffer,
+ VISIBILITYMAP_ALL_FROZEN);
+ ReleaseBuffer(vmbuffer);
+ }
+
PageSetLSN(page, lsn);
MarkBufferDirty(buffer);
}
diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c
index b472d31..c52c0b0 100644
--- a/src/backend/access/heap/visibilitymap.c
+++ b/src/backend/access/heap/visibilitymap.c
@@ -11,7 +11,7 @@
* src/backend/access/heap/visibilitymap.c
*
* INTERFACE ROUTINES
- * visibilitymap_clear - clear a bit in the visibility map
+ * visibilitymap_clear - clear all bits for one page in the visibility map
* visibilitymap_pin - pin a map page for setting a bit
* visibilitymap_pin_ok - check whether correct map page is already pinned
* visibilitymap_set - set a bit in a previously pinned page
@@ -157,23 +157,34 @@ static const uint8 number_of_ones_for_frozen[256] = {
static Buffer vm_readbuf(Relation rel, BlockNumber blkno, bool extend);
static void vm_extend(Relation rel, BlockNumber nvmblocks);
+/*
+ * A shorthand for visibilitymap_clear_extended, for clearing all bits for one
+ * page in visibility map with VISIBILITYMAP_VALID_BITS.
+ */
+void
+visibilitymap_clear(Relation rel, BlockNumber heapBlk, Buffer buf)
+{
+ visibilitymap_clear_extended(rel, heapBlk, buf, VISIBILITYMAP_VALID_BITS);
+}
/*
- * visibilitymap_clear - clear all bits for one page in visibility map
+ * visibilitymap_clear_extended - clear bit(s) for one page in visibility map
*
* You must pass a buffer containing the correct map page to this function.
* Call visibilitymap_pin first to pin the right one. This function doesn't do
* any I/O.
*/
void
-visibilitymap_clear(Relation rel, BlockNumber heapBlk, Buffer buf)
+visibilitymap_clear_extended(Relation rel, BlockNumber heapBlk, Buffer buf, uint8 flags)
{
BlockNumber mapBlock = HEAPBLK_TO_MAPBLOCK(heapBlk);
int mapByte = HEAPBLK_TO_MAPBYTE(heapBlk);
int mapOffset = HEAPBLK_TO_OFFSET(heapBlk);
- uint8 mask = VISIBILITYMAP_VALID_BITS << mapOffset;
+ uint8 mask = flags << mapOffset;
char *map;
+ Assert(flags & VISIBILITYMAP_VALID_BITS);
+
#ifdef TRACE_VISIBILITYMAP
elog(DEBUG1, "vm_clear %s %d", RelationGetRelationName(rel), heapBlk);
#endif
diff --git a/src/include/access/visibilitymap.h b/src/include/access/visibilitymap.h
index fca99ca..f305b03 100644
--- a/src/include/access/visibilitymap.h
+++ b/src/include/access/visibilitymap.h
@@ -36,6 +36,8 @@
extern void visibilitymap_clear(Relation rel, BlockNumber heapBlk,
Buffer vmbuf);
+extern void visibilitymap_clear_extended(Relation rel, BlockNumber heapBlk,
+ Buffer vmbuf, uint8 flags);
extern void visibilitymap_pin(Relation rel, BlockNumber heapBlk,
Buffer *vmbuf);
extern bool visibilitymap_pin_ok(BlockNumber heapBlk, Buffer vmbuf);
--
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