0001-Fix-the-bug-in-HS-that-it-is-possible-to-stay-connec.patch

From 36f57e6f6b1d25d7433d9706682e53cc79b45a61 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Sun, 27 Dec 2009 19:14:21 +0100
Subject: [PATCH] Fix the bug in HS that it is possible to stay connected to a database
 on a slave after it has been deleted.

Instead immediately kill sessions using such a database - it is
unlikely that those sessions will quit and its unlikely as well that
its a significant issue to get thrown of a database which is dropped
on the master.
---
 src/backend/commands/dbcommands.c   |   22 ++++++++--------------
 src/backend/storage/ipc/procarray.c |   25 +++++++++++++++++++++++++
 src/include/storage/procarray.h     |    1 +
 3 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 316222f..85d1d64 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -1945,22 +1945,16 @@ dbase_redo(XLogRecPtr lsn, XLogRecord *record)
 
 		if (InHotStandby)
 		{
-			VirtualTransactionId *database_users;
-
 			/*
-			 * Find all users connected to this database and ask them
-			 * politely to immediately kill their sessions before processing
-			 * the drop database record, after the usual grace period.
-			 * We don't wait for commit because drop database is
-			 * non-transactional.
+			 * We dont do the usual GetConflictingVirtualXIDs/
+			 * ResolveRecoveryConflictWithVirutalXIDs dance here because we are
+			 * not only conflicting against concurrently running transactions
+			 * but against concurrently running backends using this database.
+			 *
+			 * We do not wait for those sessions to exit by free will because
+			 * quite likely that will never happen. So force them.
 			 */
-		    database_users = GetConflictingVirtualXIDs(InvalidTransactionId,
-													   xlrec->db_id,
-													   false);
-
-			ResolveRecoveryConflictWithVirtualXIDs(database_users,
-												   "drop database",
-												   CONFLICT_MODE_FATAL);
+			CancelDBBackends(xlrec->db_id);
 		}
 
 		/* Drop pages for this database that are in the shared buffer cache */
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 8e2de35..07c7899 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -1827,6 +1827,31 @@ CountDBBackends(Oid databaseid)
 }
 
 /*
+ * CancelDBBackends --- cancel backends that are using specified database
+ */
+void
+CancelDBBackends(Oid databaseid)
+{
+	ProcArrayStruct *arrayP = procArray;
+	int			index;
+
+	/* tell all backends to die */
+	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+	for (index = 0; index < arrayP->numProcs; index++)
+	{
+		volatile PGPROC *proc = arrayP->procs[index];
+
+		if (proc->databaseId == databaseid){
+			if (proc->recoveryConflictMode < CONFLICT_MODE_FATAL){
+				proc->recoveryConflictMode = CONFLICT_MODE_FATAL;
+			}
+			kill(proc->pid, SIGINT);
+		}
+	}
+	LWLockRelease(ProcArrayLock);
+}
+
+/*
  * CountUserBackends --- count backends that are used by specified user
  */
 int
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index 1cee639..707396b 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -63,6 +63,7 @@ extern pid_t CancelVirtualTransaction(VirtualTransactionId vxid,
 
 extern int	CountActiveBackends(void);
 extern int	CountDBBackends(Oid databaseid);
+extern void	CancelDBBackends(Oid databaseid);
 extern int	CountUserBackends(Oid roleid);
 extern bool CountOtherDBBackends(Oid databaseId,
 					 int *nbackends, int *nprepared);
-- 
1.6.5.12.gd65df24