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commit    cf358a2c066ccb8fc9e82dc59358130aa61075ab
Author:   Andres Freund <andres@anarazel.de>
Date:     Wed Oct 31 21:47:41 2018 +0000
First released in: 12.0, 9.4.20, 9.5.15, 9.6.11, 10.6, 11.1

    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 3745edb445d..29b8cbaaf9c 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -72,6 +72,11 @@ 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 a538ae17541..909d9f3df4c 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -795,6 +795,11 @@ 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),
@@ -1236,6 +1241,31 @@ 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_ARCHIVE)
+		ereport(FATAL,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("physical replication slots \"%s\" exists, but wal_level < archive",
+						NameStr(cp.slotdata.name)),
+				 errhint("Change wal_level to be archive or higher.")));
+
 	/* nothing can be active yet, don't lock anything */
 	for (i = 0; i < max_replication_slots; i++)
 	{


[parent: 95015b1f8e8e]