At Tue, 12 Oct 2021 13:59:59 +0900 (JST), Kyotaro Horiguchi
<horikyota....@gmail.com> wrote in
> So I came up with the attached version.
Sorry, it was losing a piece of change.
--
Kyotaro Horiguchi
NTT Open Source Software Center
>From 424f405b4c9d41471eae1edd48cdbb6a6d47217e Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horikyota....@gmail.com>
Date: Tue, 12 Oct 2021 13:53:27 +0900
Subject: [PATCH v2] Allow overflowed snapshot when creating logical
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 fails for certain circumstances. Instead, create a
"takenDuringRecovery" snapshot instead, which stores all XIDs in
subxip array. Addition to that, allow to create an overflowed
snapshot by adding to reorder buffer a function to tell whether an XID
is a top-level or not.
---
.../replication/logical/reorderbuffer.c | 20 +++++++
src/backend/replication/logical/snapbuild.c | 56 +++++++++++++++----
src/include/replication/reorderbuffer.h | 1 +
3 files changed, 65 insertions(+), 12 deletions(-)
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 46e66608cf..4e452cce7c 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -3326,6 +3326,26 @@ 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 a5333349a8..46c691df20 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -531,8 +531,9 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
{
Snapshot snap;
TransactionId xid;
- TransactionId *newxip;
- int newxcnt = 0;
+ TransactionId *newsubxip;
+ int newsubxcnt;
+ bool overflowed = false;
Assert(!FirstSnapshotSet);
Assert(XactIsoLevel == XACT_REPEATABLE_READ);
@@ -568,9 +569,12 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
MyProc->xmin = snap->xmin;
- /* allocate in transaction context */
- newxip = (TransactionId *)
- palloc(sizeof(TransactionId) * GetMaxSnapshotXidCount());
+ /*
+ * Allocate in transaction context. We use only subxip to store xids. See
+ * GetSnapshotData for details.
+ */
+ newsubxip = (TransactionId *)
+ palloc(sizeof(TransactionId) * GetMaxSnapshotSubxidCount());
/*
* snapbuild.c builds transactions in an "inverted" manner, which means it
@@ -578,6 +582,9 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
* classical snapshot by marking all non-committed transactions as
* in-progress. This can be expensive.
*/
+retry:
+ newsubxcnt = 0;
+
for (xid = snap->xmin; NormalTransactionIdPrecedes(xid, snap->xmax);)
{
void *test;
@@ -591,12 +598,29 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
if (test == NULL)
{
- if (newxcnt >= GetMaxSnapshotXidCount())
- ereport(ERROR,
- (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
- errmsg("initial slot snapshot too large")));
+ bool add = true;
- newxip[newxcnt++] = xid;
+ /* exlude subxids when subxip is overflowed */
+ if (overflowed &&
+ ReorderBufferXidIsKnownSubXact(builder->reorder, xid))
+ add = false;
+
+ if (add)
+ {
+ if (newsubxcnt >= GetMaxSnapshotSubxidCount())
+ {
+ if (overflowed)
+ ereport(ERROR,
+ (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
+ errmsg("initial slot snapshot too large")));
+
+ /* retry excluding subxids */
+ overflowed = true;
+ goto retry;
+ }
+
+ newsubxip[newsubxcnt++] = xid;
+ }
}
TransactionIdAdvance(xid);
@@ -604,8 +628,16 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
/* adjust remaining snapshot fields as needed */
snap->snapshot_type = SNAPSHOT_MVCC;
- snap->xcnt = newxcnt;
- snap->xip = newxip;
+ snap->xcnt = 0;
+ snap->subxcnt = newsubxcnt;
+ snap->subxip = newsubxip;
+ snap->suboverflowed = overflowed;
+
+ /*
+ * Although this snapshot is taken actually not during recovery, all XIDs
+ * are stored in subxip even if it is not overflowed.
+ */
+ snap->takenDuringRecovery = true;
return snap;
}
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 5b40ff75f7..e5fa1051d7 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -669,6 +669,7 @@ 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
