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Optimize vector get last written LSN #553

Merged
merged 11 commits into from
Jan 14, 2025
Merged

Optimize vector get last written LSN #553

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19dab9f
Optimize vector get last written LSN
Jan 12, 2025
89d27dc
Add SetLastWrittenLSNForBlockRangeInternal to avoid redundant unlocki…
Jan 13, 2025
f7f1c57
Fix incorrect calls of SetLastWrittenLSNForBlockRangeInternal with sh…
Jan 13, 2025
94f068d
Update src/backend/access/transam/xlog.c
knizhnik Jan 13, 2025
77a1238
Update src/backend/access/transam/xlog.c
knizhnik Jan 13, 2025
2d8871f
Update comments
Jan 13, 2025
cca215e
Remove rediundant use of lsn variable
Jan 13, 2025
d7526ad
Update src/backend/access/transam/xlog.c
knizhnik Jan 13, 2025
bb48994
Update src/backend/access/transam/xlog.c
knizhnik Jan 13, 2025
e0b3210
Fix formatting
Jan 13, 2025
0f8da73
Fix bug in GetLastWrittenLSNv
Jan 13, 2025
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87 changes: 64 additions & 23 deletions src/backend/access/transam/xlog.c
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Original file line number Diff line number Diff line change
Expand Up @@ -764,6 +764,8 @@ static void WALInsertLockAcquireExclusive(void);
static void WALInsertLockRelease(void);
static void WALInsertLockUpdateInsertingAt(XLogRecPtr insertingAt);

static XLogRecPtr SetLastWrittenLSNForBlockRangeInternal(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks);
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/*
* Insert an XLOG record represented by an already-constructed chain of data
* chunks. This is a low-level routine; to construct the WAL record header
Expand Down Expand Up @@ -6681,7 +6683,7 @@ GetInsertRecPtr(void)
* either from a cached last written LSN or a global maximum last written LSN.
* If rnode is InvalidOid then we calculate maximum among all cached LSN and maxLastWrittenLsn.
* If cache is large enough, iterating through all hash items may be rather expensive.
* But GetLastWrittenLSN(InvalidOid) is used only by zenith_dbsize which is not performance critical.
* But GetLastWrittenLSN(InvalidOid) is used only by neon_dbsize which is not performance critical.
*/
XLogRecPtr
GetLastWrittenLSN(RelFileLocator rlocator, ForkNumber forknum, BlockNumber blkno)
Expand Down Expand Up @@ -6710,7 +6712,16 @@ GetLastWrittenLSN(RelFileLocator rlocator, ForkNumber forknum, BlockNumber blkno
else
{
LWLockRelease(LastWrittenLsnLock);
return SetLastWrittenLSNForBlock(lsn, rlocator, forknum, blkno);
LWLockAcquire(LastWrittenLsnLock, LW_EXCLUSIVE);
/*
* In case of statements CREATE TABLE AS SELECT... or INSERT FROM SELECT... we are fetching data from source table
* and storing it in destination table. It cause problems with prefetch last-written-lsn is known for the pages of
* source table (which for example happens after compute restart). In this case we get get global value of
* last-written-lsn which is changed frequently as far as we are writing pages of destination table.
* As a result request-lsn for the prefetch and request-let when this page is actually needed are different
* and we got exported prefetch request. So it actually disarms prefetch.
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*/
lsn = SetLastWrittenLSNForBlockRangeInternal(lsn, rlocator, forknum, blkno, 1);
}
}
else
Expand All @@ -6735,7 +6746,7 @@ GetLastWrittenLSN(RelFileLocator rlocator, ForkNumber forknum, BlockNumber blkno
* either from a cached last written LSN or a global maximum last written LSN.
* If rnode is InvalidOid then we calculate maximum among all cached LSN and maxLastWrittenLsn.
* If cache is large enough, iterating through all hash items may be rather expensive.
* But GetLastWrittenLSN(InvalidOid) is used only by zenith_dbsize which is not performance critical.
* But GetLastWrittenLSN(InvalidOid) is used only by neon_dbsize which is not performance critical.
*/
void
GetLastWrittenLSNv(RelFileLocator relfilenode, ForkNumber forknum,
Expand All @@ -6752,6 +6763,8 @@ GetLastWrittenLSNv(RelFileLocator relfilenode, ForkNumber forknum,
if (relfilenode.relNumber != InvalidOid)
{
BufferTag key;
bool missed_keys = false;

key.spcOid = relfilenode.spcOid;
key.dbOid = relfilenode.dbOid;
key.relNumber = relfilenode.relNumber;
Expand All @@ -6763,17 +6776,33 @@ GetLastWrittenLSNv(RelFileLocator relfilenode, ForkNumber forknum,
key.blockNum = blkno + i;

entry = hash_search(lastWrittenLsnCache, &key, HASH_FIND, NULL);

if (entry != NULL)
{
lsns[i] = entry->lsn;
}
else
{
XLogRecPtr lsn;
lsns[i] = lsn = XLogCtl->maxLastWrittenLsn;
/* Mark this block's LSN as missing - we'll update the LwLSN for missing blocks in bulk later */
lsns[i] = InvalidXLogRecPtr;
missed_keys = true;
}
}

/*
* If we had any missing LwLSN entries, we add the missing ones now.
* By doing the insertions in one batch, we decrease lock contention.
*/
if (missed_keys)
{
LWLockRelease(LastWrittenLsnLock);
LWLockAcquire(LastWrittenLsnLock, LW_EXCLUSIVE);

LWLockRelease(LastWrittenLsnLock);
SetLastWrittenLSNForBlock(lsn, relfilenode, forknum, key.blockNum);
LWLockAcquire(LastWrittenLsnLock, LW_SHARED);
for (int i = 0; i < nblocks; i++)
{
if (lsns[i] == InvalidXLogRecPtr)
{
SetLastWrittenLSNForBlockRangeInternal(XLogCtl->maxLastWrittenLsn, relfilenode, forknum, blkno + i, 1);
}
}
}
}
Expand All @@ -6796,22 +6825,12 @@ GetLastWrittenLSNv(RelFileLocator relfilenode, ForkNumber forknum,
}

/*
* SetLastWrittenLSNForBlockRange -- Set maximal LSN of written page range.
* We maintain cache of last written LSNs with limited size and LRU replacement
* policy. Keeping last written LSN for each page allows to use old LSN when
* requesting pages of unchanged or appended relations. Also it is critical for
* efficient work of prefetch in case massive update operations (like vacuum or remove).
*
* rlocator.relNumber can be InvalidOid, in this case maxLastWrittenLsn is updated.
* SetLastWrittenLsn with dummy rlocator is used by createdb and dbase_redo functions.
* Guts for SetLastWrittenLSNForBlockRange.
* Caller must ensure LastWrittenLsnLock is held in exclusive mode.
*/
XLogRecPtr
SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks)
static XLogRecPtr
SetLastWrittenLSNForBlockRangeInternal(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks)
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{
if (lsn == InvalidXLogRecPtr || n_blocks == 0 || lastWrittenLsnCacheSize == 0)
return lsn;

LWLockAcquire(LastWrittenLsnLock, LW_EXCLUSIVE);
if (rlocator.relNumber == InvalidOid)
{
if (lsn > XLogCtl->maxLastWrittenLsn)
Expand Down Expand Up @@ -6861,7 +6880,29 @@ SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumb
dlist_push_tail(&XLogCtl->lastWrittenLsnLRU, &entry->lru_node);
}
}
return lsn;
}

/*
* SetLastWrittenLSNForBlockRange -- Set maximal LSN of written page range.
* We maintain cache of last written LSNs with limited size and LRU replacement
* policy. Keeping last written LSN for each page allows to use old LSN when
* requesting pages of unchanged or appended relations. Also it is critical for
* efficient work of prefetch in case massive update operations (like vacuum or remove).
*
* rlocator.relNumber can be InvalidOid, in this case maxLastWrittenLsn is updated.
* SetLastWrittenLsn with dummy rlocator is used by createdb and dbase_redo functions.
*/
XLogRecPtr
SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks)
{
if (lsn == InvalidXLogRecPtr || n_blocks == 0 || lastWrittenLsnCacheSize == 0)
return lsn;

LWLockAcquire(LastWrittenLsnLock, LW_EXCLUSIVE);
lsn = SetLastWrittenLSNForBlockRangeInternal(lsn, rlocator, forknum, from, n_blocks);
LWLockRelease(LastWrittenLsnLock);

return lsn;
}

Expand Down