Add information of total data processed to replication slot stats.

This adds the statistics about total transactions count and total
transaction data logically sent to the decoding output plugin from
ReorderBuffer. Users can query the pg_stat_replication_slots view to check
these stats.

Suggested-by: Andres Freund
Author: Vignesh C and Amit Kapila
Reviewed-by: Sawada Masahiko, Amit Kapila
Discussion: https://postgr.es/m/20210319185247.ldebgpdaxsowiflw@alap3.anarazel.de

1 files changed, 34 insertions, 14 deletions

diff --git a/contrib/test_decoding/sql/stats.sql b/contrib/test_decoding/sql/stats.sql
index 51294e48e87..8c34aeced1d 100644
--- a/contrib/test_decoding/sql/stats.sql
+++ b/contrib/test_decoding/sql/stats.sql
@@ -6,7 +6,7 @@ SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_d
 CREATE TABLE stats_test(data text);
 
 -- function to wait for counters to advance
-CREATE FUNCTION wait_for_decode_stats(check_reset bool) RETURNS void AS $$
+CREATE FUNCTION wait_for_decode_stats(check_reset bool, check_spill_txns bool) RETURNS void AS $$
 DECLARE
   start_time timestamptz := clock_timestamp();
   updated bool;
@@ -14,12 +14,25 @@ BEGIN
   -- we don't want to wait forever; loop will exit after 30 seconds
   FOR i IN 1 .. 300 LOOP
 
-    -- check to see if all updates have been reset/updated
-    SELECT CASE WHEN check_reset THEN (spill_txns = 0)
-                ELSE (spill_txns > 0)
-           END
-    INTO updated
-    FROM pg_stat_replication_slots WHERE slot_name='regression_slot';
+    IF check_spill_txns THEN
+
+      -- check to see if all updates have been reset/updated
+      SELECT CASE WHEN check_reset THEN (spill_txns = 0)
+                  ELSE (spill_txns > 0)
+             END
+      INTO updated
+      FROM pg_stat_replication_slots WHERE slot_name='regression_slot';
+
+    ELSE
+
+      -- check to see if all updates have been reset/updated
+      SELECT CASE WHEN check_reset THEN (total_txns = 0)
+                  ELSE (total_txns > 0)
+             END
+      INTO updated
+      FROM pg_stat_replication_slots WHERE slot_name='regression_slot';
+
+    END IF;
 
     exit WHEN updated;
 
@@ -46,18 +59,25 @@ SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL,
 -- Check stats, wait for the stats collector to update. We can't test the
 -- exact stats count as that can vary if any background transaction (say by
 -- autovacuum) happens in parallel to the main transaction.
-SELECT wait_for_decode_stats(false);
-SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count FROM pg_stat_replication_slots;
+SELECT wait_for_decode_stats(false, true);
+SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
 
 -- reset the slot stats, and wait for stats collector to reset
 SELECT pg_stat_reset_replication_slot('regression_slot');
-SELECT wait_for_decode_stats(true);
-SELECT slot_name, spill_txns, spill_count FROM pg_stat_replication_slots;
+SELECT wait_for_decode_stats(true, true);
+SELECT slot_name, spill_txns, spill_count, total_txns, total_bytes FROM pg_stat_replication_slots;
 
 -- decode and check stats again.
 SELECT count(*) FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL, 'skip-empty-xacts', '1');
-SELECT wait_for_decode_stats(false);
-SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count FROM pg_stat_replication_slots;
+SELECT wait_for_decode_stats(false, true);
+SELECT slot_name, spill_txns > 0 AS spill_txns, spill_count > 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
+
+SELECT pg_stat_reset_replication_slot('regression_slot');
+
+-- non-spilled xact
+INSERT INTO stats_test values(generate_series(1, 10));
+SELECT wait_for_decode_stats(false, false);
+SELECT slot_name, spill_txns = 0 AS spill_txns, spill_count = 0 AS spill_count, total_txns > 0 AS total_txns, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots;
 
 -- Ensure stats can be repeatedly accessed using the same stats snapshot. See
 -- https://postgr.es/m/20210317230447.c7uc4g3vbs4wi32i%40alap3.anarazel.de
@@ -66,6 +86,6 @@ SELECT slot_name FROM pg_stat_replication_slots;
 SELECT slot_name FROM pg_stat_replication_slots;
 COMMIT;
 
-DROP FUNCTION wait_for_decode_stats(bool);
+DROP FUNCTION wait_for_decode_stats(bool, bool);
 DROP TABLE stats_test;
 SELECT pg_drop_replication_slot('regression_slot');