At Fri, 01 Apr 2022 14:44:30 +0900 (JST), Kyotaro Horiguchi
<horikyota....@gmail.com> wrote in
> At Sun, 13 Feb 2022 17:35:38 +0300, Yura Sokolov <y.soko...@postgrespro.ru>
> wrote in
> > And there are checks for `takenDuringRecovery` in `heapgetpage` and
> > `heapam_scan_sample_next_tuple`. Are this checks affected by the change?
> > Neither the preceding discussion nor commit message answer me.
>
> The snapshot works correctly, but for the heapgetpage case, it foces
> all_visible to be false. That unnecessarily prevents visibility check
> from skipping.
>
> An annoying thing in SnapBuildInitialSnapshot is that we don't know
> the number of xids before looping over the xid range, and we don't
> want to bother sorting top-level xids and subxids unless we have to do
> so.
>
> Is it better that we hassle in SnapBuildInitialSnapshot to create a
> !takenDuringRecovery snapshot?
So this is that. v5 creates a regular snapshot.
By the way, is there any chance this could be committed to 15?
Otherwise I'll immediately move this to the next CF.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
>From 6f3cfb58bc2c6294124831d6b410b0e51d067fb2 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horikyota....@gmail.com>
Date: Mon, 31 Jan 2022 15:03:33 +0900
Subject: [PATCH v5] Create correct snapshot during CREATE_REPLICATION_SLOT
Snapshot can hold top XIDs up to the number of server processes but
SnapBuildInitialSnapshot tries to store all top-level and sub XIDs to
there and easily fails with "initial slot snapshot too large" error.
We could instead create a "takenDuringRecovery" snapshot, which later
leads to unnecessary visibility checks. Therefore we take trouble to
create a regular snapshot by identifying whether each xids is
top-level and storing it in the appropriate xid array.
Author: Dilip Kumar and Kyotaro Horiguchi
---
.../replication/logical/reorderbuffer.c | 20 +++++++++
src/backend/replication/logical/snapbuild.c | 45 +++++++++++++++----
src/include/replication/reorderbuffer.h | 1 +
3 files changed, 58 insertions(+), 8 deletions(-)
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index c2d9be81fa..42adbe5f15 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -3658,6 +3658,26 @@ ReorderBufferXidHasBaseSnapshot(ReorderBuffer *rb, TransactionId xid)
}
+/*
+ * ReorderBufferXidIsKnownSubXact
+ * Returns true if the xid is a known subtransaction.
+ */
+bool
+ReorderBufferXidIsKnownSubXact(ReorderBuffer *rb, TransactionId xid)
+{
+ ReorderBufferTXN *txn;
+
+ txn = ReorderBufferTXNByXid(rb, xid, false,
+ NULL, InvalidXLogRecPtr, false);
+
+ /* a known subtxn? */
+ if (txn && rbtxn_is_known_subxact(txn))
+ return true;
+
+ return false;
+}
+
+
/*
* ---------------------------------------
* Disk serialization support
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 83fca8a77d..fa08e406e3 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -532,7 +532,10 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
Snapshot snap;
TransactionId xid;
TransactionId *newxip;
- int newxcnt = 0;
+ TransactionId *newsubxip;
+ int newxcnt;
+ int newsubxcnt;
+ bool overflowed = false;
Assert(!FirstSnapshotSet);
Assert(XactIsoLevel == XACT_REPEATABLE_READ);
@@ -568,9 +571,17 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
MyProc->xmin = snap->xmin;
- /* allocate in transaction context */
+ /*
+ * Allocate in transaction context.
+ *
+ * We could use only subxip to store all xids (takenduringrecovery
+ * snapshot) but that causes useless visibility checks later so we hasle to
+ * create a normal snapshot.
+ */
newxip = (TransactionId *)
palloc(sizeof(TransactionId) * GetMaxSnapshotXidCount());
+ newsubxip = (TransactionId *)
+ palloc(sizeof(TransactionId) * GetMaxSnapshotSubxidCount());
/*
* snapbuild.c builds transactions in an "inverted" manner, which means it
@@ -578,6 +589,9 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
* classical snapshot by marking all non-committed transactions as
* in-progress. This can be expensive.
*/
+ newxcnt = 0;
+ newsubxcnt = 0;
+
for (xid = snap->xmin; NormalTransactionIdPrecedes(xid, snap->xmax);)
{
void *test;
@@ -591,12 +605,24 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
if (test == NULL)
{
- if (newxcnt >= GetMaxSnapshotXidCount())
- ereport(ERROR,
- (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
- errmsg("initial slot snapshot too large")));
-
- newxip[newxcnt++] = xid;
+ /* Store the xid to the appropriate xid array */
+ if (ReorderBufferXidIsKnownSubXact(builder->reorder, xid))
+ {
+ if (!overflowed)
+ {
+ if (newsubxcnt >= GetMaxSnapshotSubxidCount())
+ overflowed = true;
+ else
+ newsubxip[newsubxcnt++] = xid;
+ }
+ }
+ else
+ {
+ if (newxcnt >= GetMaxSnapshotXidCount())
+ elog(ERROR,
+ "too many transactions while creating snapshot");
+ newxip[newxcnt++] = xid;
+ }
}
TransactionIdAdvance(xid);
@@ -606,6 +632,9 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
snap->snapshot_type = SNAPSHOT_MVCC;
snap->xcnt = newxcnt;
snap->xip = newxip;
+ snap->subxcnt = newsubxcnt;
+ snap->subxip = newsubxip;
+ snap->suboverflowed = overflowed;
return snap;
}
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 0bcc150b33..b26c34ce9d 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -707,6 +707,7 @@ void ReorderBufferXidSetCatalogChanges(ReorderBuffer *, TransactionId xid, XLog
bool ReorderBufferXidHasCatalogChanges(ReorderBuffer *, TransactionId xid);
bool ReorderBufferXidHasBaseSnapshot(ReorderBuffer *, TransactionId xid);
+bool ReorderBufferXidIsKnownSubXact(ReorderBuffer *rb, TransactionId xid);
bool ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
XLogRecPtr prepare_lsn, XLogRecPtr end_lsn,
TimestampTz prepare_time,
--
2.27.0
