pgstat: revise replication slot API in preparation for shared memory stats.

Previously the pgstat <-> replication slots API was done with on the basis of
names. However, the upcoming move to storing stats in shared memory makes it
more convenient to use a integer as key.

Change the replication slot functions to take the slot rather than the slot
name, and expose ReplicationSlotIndex() to compute the index of an replication
slot. Special handling will be required for restarts, as the index is not
stable across restarts. For now pgstat internally still uses names.

Rename pgstat_report_replslot_{create,drop}() to
pgstat_{create,drop}_replslot() to match the functions for other kinds of
stats.

Reviewed-By: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20220404041516.cctrvpadhuriawlq@alap3.anarazel.de

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 13dee84059337a5b87dc53565d92bd7d2a0192f5..8655b56c5e2734b961683e05251be5e17803ae83 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -862,7 +862,15 @@ pgstat_vacuum_stat(void)
            CHECK_FOR_INTERRUPTS();
 
            if (SearchNamedReplicationSlot(NameStr(slotentry->slotname), true) == NULL)
-               pgstat_report_replslot_drop(NameStr(slotentry->slotname));
+           {
+               PgStat_MsgReplSlot msg;
+
+               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_REPLSLOT);
+               namestrcpy(&msg.m_slotname, NameStr(slotentry->slotname));
+               msg.m_create = false;
+               msg.m_drop = true;
+               pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));
+           }
        }
    }
 

diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index e1f14aeecb5efea93c6eb9c79ffee6ab15193f49..656ec8f5555b2626c0e600ee82ea110a249e9ede 100644 (file)
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -1921,7 +1921,7 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
    repSlotStat.total_txns = rb->totalTxns;
    repSlotStat.total_bytes = rb->totalBytes;
 
-   pgstat_report_replslot(&repSlotStat);
+   pgstat_report_replslot(ctx->slot, &repSlotStat);
 
    rb->spillTxns = 0;
    rb->spillCount = 0;

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index ed4c8b3ad5586839fa4c22b8885dd4d43d3b45bd..2217af70d43cf8473e52ed7d6b13e0eb8ab8a329 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -356,7 +356,7 @@ ReplicationSlotCreate(const char *name, bool db_specific,
     * ReplicationSlotAllocationLock.
     */
    if (SlotIsLogical(slot))
-       pgstat_report_replslot_create(NameStr(slot->data.name));
+       pgstat_create_replslot(slot);
 
    /*
     * Now that the slot has been marked as in_use and active, it's safe to
@@ -399,6 +399,22 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
    return slot;
 }
 
+/*
+ * Return the index of the replication slot in
+ * ReplicationSlotCtl->replication_slots.
+ *
+ * This is mainly useful to have an efficient key for storing replication slot
+ * stats.
+ */
+int
+ReplicationSlotIndex(ReplicationSlot *slot)
+{
+   Assert(slot >= ReplicationSlotCtl->replication_slots &&
+          slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+
+   return slot - ReplicationSlotCtl->replication_slots;
+}
+
 /*
  * Find a previously created slot and mark it as used by this process.
  *
@@ -746,7 +762,7 @@ ReplicationSlotDropPtr(ReplicationSlot *slot)
     * doesn't seem worth doing as in practice this won't happen frequently.
     */
    if (SlotIsLogical(slot))
-       pgstat_report_replslot_drop(NameStr(slot->data.name));
+       pgstat_drop_replslot(slot);
 
    /*
     * We release this at the very end, so that nobody starts trying to create

diff --git a/src/backend/utils/activity/pgstat_replslot.c b/src/backend/utils/activity/pgstat_replslot.c
index cfaf8d546c55a5e128e4407f3335327e026d5794..ceefc5d59b3a0e7f3548434cfcc90e043fa7ad5a 100644 (file)
--- a/src/backend/utils/activity/pgstat_replslot.c
+++ b/src/backend/utils/activity/pgstat_replslot.c
@@ -69,7 +69,7 @@ pgstat_reset_replslot(const char *name)
  * Report replication slot statistics.
  */
 void
-pgstat_report_replslot(const PgStat_StatReplSlotEntry *repSlotStat)
+pgstat_report_replslot(ReplicationSlot *slot, const PgStat_StatReplSlotEntry *repSlotStat)
 {
    PgStat_MsgReplSlot msg;
 
@@ -93,14 +93,17 @@ pgstat_report_replslot(const PgStat_StatReplSlotEntry *repSlotStat)
 
 /*
  * Report replication slot creation.
+ *
+ * NB: This gets called with ReplicationSlotAllocationLock already held, be
+ * careful about calling back into slot.c.
  */
 void
-pgstat_report_replslot_create(const char *slotname)
+pgstat_create_replslot(ReplicationSlot *slot)
 {
    PgStat_MsgReplSlot msg;
 
    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_REPLSLOT);
-   namestrcpy(&msg.m_slotname, slotname);
+   namestrcpy(&msg.m_slotname, NameStr(slot->data.name));
    msg.m_create = true;
    msg.m_drop = false;
    pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));
@@ -110,12 +113,12 @@ pgstat_report_replslot_create(const char *slotname)
  * Report replication slot drop.
  */
 void
-pgstat_report_replslot_drop(const char *slotname)
+pgstat_drop_replslot(ReplicationSlot *slot)
 {
    PgStat_MsgReplSlot msg;
 
    pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_REPLSLOT);
-   namestrcpy(&msg.m_slotname, slotname);
+   namestrcpy(&msg.m_slotname, NameStr(slot->data.name));
    msg.m_create = false;
    msg.m_drop = true;
    pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 7981a816565c6610f7934bb1a5997bc14fe4e16d..0c618e77103b21fa1c171661ee0f5a03d735fbf8 100644 (file)
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -1137,9 +1137,10 @@ extern PgStat_TableStatus *find_tabstat_entry(Oid rel_id);
  */
 
 extern void pgstat_reset_replslot(const char *name);
-extern void pgstat_report_replslot(const PgStat_StatReplSlotEntry *repSlotStat);
-extern void pgstat_report_replslot_create(const char *slotname);
-extern void pgstat_report_replslot_drop(const char *slotname);
+struct ReplicationSlot;
+extern void pgstat_report_replslot(struct ReplicationSlot *slot, const PgStat_StatReplSlotEntry *repSlotStat);
+extern void pgstat_create_replslot(struct ReplicationSlot *slot);
+extern void pgstat_drop_replslot(struct ReplicationSlot *slot);
 
 
 /*

diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 24b30210c3e08c622e1b423a169e0fcf5f8b3961..1ee63c4cf44e925a5c795fa50578069289a320d1 100644 (file)
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -216,6 +216,7 @@ extern bool ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive);
 extern void ReplicationSlotsDropDBSlots(Oid dboid);
 extern bool InvalidateObsoleteReplicationSlots(XLogSegNo oldestSegno);
 extern ReplicationSlot *SearchNamedReplicationSlot(const char *name, bool need_lock);
+extern int ReplicationSlotIndex(ReplicationSlot *slot);
 extern void ReplicationSlotNameForTablesync(Oid suboid, Oid relid, char *syncslotname, int szslot);
 extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname, bool missing_ok);