From 3baf804b7295fff7551f93ed94550d8268804cc1 Mon Sep 17 00:00:00 2001
From: Noah Misch <noah@leadboat.com>
Date: Fri, 25 Oct 2024 06:51:06 -0700
Subject: [PATCH] At end of recovery, reset all sinval-managed caches.

An inplace update's invalidation messages are part of its transaction's
commit record.  However, the update survives even if its transaction
aborts or we stop recovery before replaying its transaction commit.
After recovery, a backend that started in recovery could update the row
without incorporating the inplace update.  That could result in a table
with an index, yet relhasindex=f.  That is a source of index corruption.

This bulk invalidation avoids the functional consequences.  A future
change can fix the !RecoveryInProgress() scenario without changing the
WAL format.  Back-patch to v17 - v12 (all supported versions).  v18 will
instead add invalidations to WAL.

Discussion: https://postgr.es/m/20240618152349.7f.nmisch@google.com
---
 src/backend/access/transam/xlog.c   | 25 ++++++++++++++++++
 src/backend/storage/ipc/sinvaladt.c | 41 +++++++++++++++++++++++++++++
 src/include/storage/sinvaladt.h     |  1 +
 3 files changed, 67 insertions(+)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index daad1ff1c3b..5d8322fbd04 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -94,6 +94,7 @@
 #include "storage/proc.h"
 #include "storage/procarray.h"
 #include "storage/reinit.h"
+#include "storage/sinvaladt.h"
 #include "storage/smgr.h"
 #include "storage/spin.h"
 #include "storage/sync.h"
@@ -5514,6 +5515,30 @@ StartupXLOG(void)
 	XLogCtl->LogwrtRqst.Write = EndOfLog;
 	XLogCtl->LogwrtRqst.Flush = EndOfLog;
 
+	/*
+	 * Invalidate all sinval-managed caches before READ WRITE transactions
+	 * begin.  The xl_heap_inplace WAL record doesn't store sufficient data
+	 * for invalidations.  The commit record, if any, has the invalidations.
+	 * However, the inplace update is permanent, whether or not we reach a
+	 * commit record.  Fortunately, read-only transactions tolerate caches not
+	 * reflecting the latest inplace updates.  Read-only transactions
+	 * experience the notable inplace updates as follows:
+	 *
+	 * - relhasindex=true affects readers only after the CREATE INDEX
+	 * transaction commit makes an index fully available to them.
+	 *
+	 * - datconnlimit=DATCONNLIMIT_INVALID_DB affects readers only at
+	 * InitPostgres() time, and that read does not use a cache.
+	 *
+	 * - relfrozenxid, datfrozenxid, relminmxid, and datminmxid have no effect
+	 * on readers.
+	 *
+	 * Hence, hot standby queries (all READ ONLY) function correctly without
+	 * the missing invalidations.  This avoided changing the WAL format in
+	 * back branches.
+	 */
+	SIResetAll();
+
 	/*
 	 * Preallocate additional log files, if wanted.
 	 */
diff --git a/src/backend/storage/ipc/sinvaladt.c b/src/backend/storage/ipc/sinvaladt.c
index 59310b708fb..21f0ff97579 100644
--- a/src/backend/storage/ipc/sinvaladt.c
+++ b/src/backend/storage/ipc/sinvaladt.c
@@ -757,6 +757,47 @@ SICleanupQueue(bool callerHasWriteLock, int minFree)
 	}
 }
 
+/*
+ * SIResetAll
+ *		Mark all active backends as "reset"
+ *
+ * Use this when we don't know what needs to be invalidated.  It's a
+ * cluster-wide InvalidateSystemCaches().  This was a back-branch-only remedy
+ * to avoid a WAL format change.
+ *
+ * The implementation is like SICleanupQueue(false, MAXNUMMESSAGES + 1), with
+ * one addition.  SICleanupQueue() assumes minFree << MAXNUMMESSAGES, so it
+ * assumes hasMessages==true for any backend it resets.  We're resetting even
+ * fully-caught-up backends, so we set hasMessages.
+ */
+void
+SIResetAll(void)
+{
+	SISeg	   *segP = shmInvalBuffer;
+	int			i;
+
+	LWLockAcquire(SInvalWriteLock, LW_EXCLUSIVE);
+	LWLockAcquire(SInvalReadLock, LW_EXCLUSIVE);
+
+	for (i = 0; i < segP->lastBackend; i++)
+	{
+		ProcState  *stateP = &segP->procState[i];
+
+		if (stateP->procPid == 0 || stateP->sendOnly)
+			continue;
+
+		/* Consuming the reset will update "nextMsgNum" and "signaled". */
+		stateP->resetState = true;
+		stateP->hasMessages = true;
+	}
+
+	segP->minMsgNum = segP->maxMsgNum;
+	segP->nextThreshold = CLEANUP_MIN;
+
+	LWLockRelease(SInvalReadLock);
+	LWLockRelease(SInvalWriteLock);
+}
+
 
 /*
  * GetNextLocalTransactionId --- allocate a new LocalTransactionId
diff --git a/src/include/storage/sinvaladt.h b/src/include/storage/sinvaladt.h
index 91e24189a7a..b3a83ccae20 100644
--- a/src/include/storage/sinvaladt.h
+++ b/src/include/storage/sinvaladt.h
@@ -37,6 +37,7 @@ extern void BackendIdGetTransactionIds(int backendID, TransactionId *xid, Transa
 extern void SIInsertDataEntries(const SharedInvalidationMessage *data, int n);
 extern int	SIGetDataEntries(SharedInvalidationMessage *data, int datasize);
 extern void SICleanupQueue(bool callerHasWriteLock, int minFree);
+extern void SIResetAll(void);
 
 extern LocalTransactionId GetNextLocalTransactionId(void);