Properly re-initialize replication slot shared memory upon creation.

Slot creation did not clear all fields upon creation. After start the
memory is zeroed, but when a physical replication slot was created in
the shared memory of a previously existing logical slot, catalog_xmin
would not be cleared. That in turn would prevent vacuum from doing its
duties.

To fix initialize all the fields. To make similar future bugs less
likely, zero all of ReplicationSlotPersistentData, and re-order the
rest of the initialization to be in struct member order.

Analysis: Andrew Gierth
Reported-By: md@chewy.com
Author: Michael Paquier
Discussion: <20160705173502.1398.70934@wrigleys.postgresql.org>
Backpatch: 9.4, where replication slots were introduced

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 2fb7c17d7da6745848bacc417f6c7550699a1ab0..0b2575ee9d0b3b9f7b418202d2c7c0293bf1aba6 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -272,12 +272,22 @@ ReplicationSlotCreate(const char *name, bool db_specific,
         */
        Assert(!slot->in_use);
        Assert(slot->active_pid == 0);
-       slot->data.persistency = persistency;
-       slot->data.xmin = InvalidTransactionId;
-       slot->effective_xmin = InvalidTransactionId;
+
+       /* first initialize persistent data */
+       memset(&slot->data, 0, sizeof(ReplicationSlotPersistentData));
        StrNCpy(NameStr(slot->data.name), name, NAMEDATALEN);
        slot->data.database = db_specific ? MyDatabaseId : InvalidOid;
-       slot->data.restart_lsn = InvalidXLogRecPtr;
+       slot->data.persistency = persistency;
+
+       /* and then data only present in shared memory */
+       slot->just_dirtied = false;
+       slot->dirty = false;
+       slot->effective_xmin = InvalidTransactionId;
+       slot->effective_catalog_xmin = InvalidTransactionId;
+       slot->candidate_catalog_xmin = InvalidTransactionId;
+       slot->candidate_xmin_lsn = InvalidXLogRecPtr;
+       slot->candidate_restart_valid = InvalidXLogRecPtr;
+       slot->candidate_restart_lsn = InvalidXLogRecPtr;
 
        /*
         * Create the slot on disk.  We haven't actually marked the slot allocated