Replace replication slot's invalidated_at LSN with an enum

This is mainly useful because the upcoming logical-decoding-on-standby feature
adds further reasons for invalidating slots, and we don't want to end up with
multiple invalidated_* fields, or check different attributes.

Eventually we should consider not resetting restart_lsn when invalidating a
slot due to max_slot_wal_keep_size. But that's a user visible change, so left
for later.

Increases SLOT_VERSION, due to the changed field (with a different alignment,
no less).

Reviewed-by: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/20230407075009.igg7be27ha2htkbt@awork3.anarazel.de

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 2293c0c6fc348b0a1541c2ed666977b73fd67639..f969f7c083f97c2fb8f8af17763332e8d639f4ea 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -89,7 +89,7 @@ typedef struct ReplicationSlotOnDisk
    sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskConstantSize
 
 #define SLOT_MAGIC     0x1051CA1   /* format identifier */
-#define SLOT_VERSION   2       /* version for new files */
+#define SLOT_VERSION   3       /* version for new files */
 
 /* Control array for replication slot management */
 ReplicationSlotCtlData *ReplicationSlotCtl = NULL;
@@ -855,8 +855,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
        SpinLockAcquire(&s->mutex);
        effective_xmin = s->effective_xmin;
        effective_catalog_xmin = s->effective_catalog_xmin;
-       invalidated = (!XLogRecPtrIsInvalid(s->data.invalidated_at) &&
-                      XLogRecPtrIsInvalid(s->data.restart_lsn));
+       invalidated = s->data.invalidated != RS_INVAL_NONE;
        SpinLockRelease(&s->mutex);
 
        /* invalidated slots need not apply */
@@ -901,14 +900,20 @@ ReplicationSlotsComputeRequiredLSN(void)
    {
        ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
        XLogRecPtr  restart_lsn;
+       bool        invalidated;
 
        if (!s->in_use)
            continue;
 
        SpinLockAcquire(&s->mutex);
        restart_lsn = s->data.restart_lsn;
+       invalidated = s->data.invalidated != RS_INVAL_NONE;
        SpinLockRelease(&s->mutex);
 
+       /* invalidated slots need not apply */
+       if (invalidated)
+           continue;
+
        if (restart_lsn != InvalidXLogRecPtr &&
            (min_required == InvalidXLogRecPtr ||
             restart_lsn < min_required))
@@ -946,6 +951,7 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
    {
        ReplicationSlot *s;
        XLogRecPtr  restart_lsn;
+       bool        invalidated;
 
        s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -960,8 +966,13 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
        /* read once, it's ok if it increases while we're checking */
        SpinLockAcquire(&s->mutex);
        restart_lsn = s->data.restart_lsn;
+       invalidated = s->data.invalidated != RS_INVAL_NONE;
        SpinLockRelease(&s->mutex);
 
+       /* invalidated slots need not apply */
+       if (invalidated)
+           continue;
+
        if (restart_lsn == InvalidXLogRecPtr)
            continue;
 
@@ -1012,6 +1023,8 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
        if (s->data.database != dboid)
            continue;
 
+       /* NB: intentionally counting invalidated slots */
+
        /* count slots with spinlock held */
        SpinLockAcquire(&s->mutex);
        (*nslots)++;
@@ -1069,6 +1082,8 @@ restart:
        if (s->data.database != dboid)
            continue;
 
+       /* NB: intentionally including invalidated slots */
+
        /* acquire slot, so ReplicationSlotDropAcquired can be reused  */
        SpinLockAcquire(&s->mutex);
        /* can't change while ReplicationSlotControlLock is held */
@@ -1294,7 +1309,12 @@ InvalidatePossiblyObsoleteSlot(ReplicationSlot *s, XLogRecPtr oldestLSN,
        {
            MyReplicationSlot = s;
            s->active_pid = MyProcPid;
-           s->data.invalidated_at = restart_lsn;
+           s->data.invalidated = RS_INVAL_WAL_REMOVED;
+
+           /*
+            * XXX: We should consider not overwriting restart_lsn and instead
+            * just rely on .invalidated.
+            */
            s->data.restart_lsn = InvalidXLogRecPtr;
 
            /* Let caller know */

diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 2f3c96482413324de00675765229351733d8c54b..ad3e72be5ee2634983ab39804843aa48a9e2194e 100644 (file)
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -315,12 +315,10 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
            nulls[i++] = true;
 
        /*
-        * If invalidated_at is valid and restart_lsn is invalid, we know for
-        * certain that the slot has been invalidated.  Otherwise, test
-        * availability from restart_lsn.
+        * If the slot has not been invalidated, test availability from
+        * restart_lsn.
         */
-       if (XLogRecPtrIsInvalid(slot_contents.data.restart_lsn) &&
-           !XLogRecPtrIsInvalid(slot_contents.data.invalidated_at))
+       if (slot_contents.data.invalidated != RS_INVAL_NONE)
            walstate = WALAVAIL_REMOVED;
        else
            walstate = GetWALAvailability(slot_contents.data.restart_lsn);

diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 8872c80cdfe7f6db9602b3152119c2e1844767eb..34ce055dd503d4a59c52065cd52d55806f48fec3 100644 (file)
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -37,6 +37,17 @@ typedef enum ReplicationSlotPersistency
    RS_TEMPORARY
 } ReplicationSlotPersistency;
 
+/*
+ * Slots can be invalidated, e.g. due to max_slot_wal_keep_size. If so, the
+ * 'invalidated' field is set to a value other than _NONE.
+ */
+typedef enum ReplicationSlotInvalidationCause
+{
+   RS_INVAL_NONE,
+   /* required WAL has been removed */
+   RS_INVAL_WAL_REMOVED,
+} ReplicationSlotInvalidationCause;
+
 /*
  * On-Disk data of a replication slot, preserved across restarts.
  */
@@ -72,8 +83,8 @@ typedef struct ReplicationSlotPersistentData
    /* oldest LSN that might be required by this replication slot */
    XLogRecPtr  restart_lsn;
 
-   /* restart_lsn is copied here when the slot is invalidated */
-   XLogRecPtr  invalidated_at;
+   /* RS_INVAL_NONE if valid, or the reason for having been invalidated */
+   ReplicationSlotInvalidationCause invalidated;
 
    /*
     * Oldest LSN that the client has acked receipt for.  This is used as the

diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index df960883c5ce3f69338683e58eb07219bb799555..b4058b88c3e9ef319d1677e13bbbf6bb3165ab4c 100644 (file)
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2339,6 +2339,7 @@ ReplicaIdentityStmt
 ReplicationKind
 ReplicationSlot
 ReplicationSlotCtlData
+ReplicationSlotInvalidationCause
 ReplicationSlotOnDisk
 ReplicationSlotPersistency
 ReplicationSlotPersistentData