From d35fd17cb58db72122912b57c75c8825ebf24285 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 31 Oct 2018 14:47:41 -0700
Subject: [PATCH] Disallow starting server with insufficient wal_level for
existing slot.
Previously it was possible to create a slot, change wal_level, and
restart, even if the new wal_level was insufficient for the
slot. That's a problem for both logical and physical slots, because
the necessary WAL records are not generated.
This removes a few tests in newer versions that, somewhat
inexplicably, whether restarting with a too low wal_level worked (a
buggy behaviour!).
Reported-By: Joshua D. Drake
Author: Andres Freund
Discussion: https://postgr.es/m/20181029191304.lbsmhshkyymhw22w@alap3.anarazel.de
Backpatch: 9.4-, where replication slots where introduced
---
src/backend/replication/logical/logical.c | 5 ++++
src/backend/replication/slot.c | 30 +++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f44533eb7f7..f9ae9cb2d9a 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -77,6 +77,11 @@ CheckLogicalDecodingRequirements(void)
{
CheckSlotRequirements();
+ /*
+ * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
+ * needs the same check.
+ */
+
if (wal_level < WAL_LEVEL_LOGICAL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a206fbf234d..f914153f1b3 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -783,6 +783,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
void
CheckSlotRequirements(void)
{
+ /*
+ * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
+ * needs the same check.
+ */
+
if (max_replication_slots == 0)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
@@ -1286,6 +1291,31 @@ RestoreSlotFromDisk(const char *name)
return;
}
+ /*
+ * Verify that requirements for the specific slot type are met. That's
+ * important because if these aren't met we're not guaranteed to retain
+ * all the necessary resources for the slot.
+ *
+ * NB: We have to do so *after* the above checks for ephemeral slots,
+ * because otherwise a slot that shouldn't exist anymore could prevent
+ * restarts.
+ *
+ * NB: Changing the requirements here also requires adapting
+ * CheckSlotRequirements() and CheckLogicalDecodingRequirements().
+ */
+ if (cp.slotdata.database != InvalidOid && wal_level < WAL_LEVEL_LOGICAL)
+ ereport(FATAL,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("logical replication slots \"%s\" exists, but wal_level < logical",
+ NameStr(cp.slotdata.name)),
+ errhint("Change wal_level to be replica or higher.")));
+ else if (wal_level < WAL_LEVEL_REPLICA)
+ ereport(FATAL,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("physical replication slots \"%s\" exists, but wal_level < replica",
+ NameStr(cp.slotdata.name)),
+ errhint("Change wal_level to be replica or higher.")));
+
/* nothing can be active yet, don't lock anything */
for (i = 0; i < max_replication_slots; i++)
{
--
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