Add pg_stat_get_snapshot_timestamp() to show statistics snapshot timestamp.

Per discussion, this could be useful for purposes such as programmatically
detecting a nonresponding stats collector.  We already have the timestamp
anyway, it's just a matter of providing a SQL-accessible function to fetch
it.

Matt Kelly, reviewed by Jim Nasby

2 files changed, 14 insertions, 2 deletions

diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index ec0ff6589b8..86319718591 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -28,7 +28,8 @@ SELECT pg_sleep_for('2 seconds');
 CREATE TEMP TABLE prevstats AS
 SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
        (b.heap_blks_read + b.heap_blks_hit) AS heap_blks,
-       (b.idx_blks_read + b.idx_blks_hit) AS idx_blks
+       (b.idx_blks_read + b.idx_blks_hit) AS idx_blks,
+       pg_stat_get_snapshot_timestamp() as snap_ts
   FROM pg_catalog.pg_stat_user_tables AS t,
        pg_catalog.pg_statio_user_tables AS b
  WHERE t.relname='tenk2' AND b.relname='tenk2';
@@ -111,4 +112,11 @@ SELECT st.heap_blks_read + st.heap_blks_hit >= pr.heap_blks + cl.relpages,
  t        | t
 (1 row)
 
+SELECT pr.snap_ts < pg_stat_get_snapshot_timestamp() as snapshot_newer
+FROM prevstats AS pr;
+ snapshot_newer 
+----------------
+ t
+(1 row)
+
 -- End of Stats Test
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 646b9ac6869..16163008308 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -22,7 +22,8 @@ SELECT pg_sleep_for('2 seconds');
 CREATE TEMP TABLE prevstats AS
 SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
        (b.heap_blks_read + b.heap_blks_hit) AS heap_blks,
-       (b.idx_blks_read + b.idx_blks_hit) AS idx_blks
+       (b.idx_blks_read + b.idx_blks_hit) AS idx_blks,
+       pg_stat_get_snapshot_timestamp() as snap_ts
   FROM pg_catalog.pg_stat_user_tables AS t,
        pg_catalog.pg_statio_user_tables AS b
  WHERE t.relname='tenk2' AND b.relname='tenk2';
@@ -81,4 +82,7 @@ SELECT st.heap_blks_read + st.heap_blks_hit >= pr.heap_blks + cl.relpages,
   FROM pg_statio_user_tables AS st, pg_class AS cl, prevstats AS pr
  WHERE st.relname='tenk2' AND cl.relname='tenk2';
 
+SELECT pr.snap_ts < pg_stat_get_snapshot_timestamp() as snapshot_newer
+FROM prevstats AS pr;
+
 -- End of Stats Test