PG-345: Add tap test for missing queries.

This test ensures that pg_stat_monitor moves only pending queries to the
next bucket when transitioning to a new one, also check that it keeps
the finished queries in the original bucket.

t/023_missing_queries.pl

@@ -0,0 +1,99 @@
+#!/usr/bin/perl
+
+# Tap test for PG-291 / eb4087be4e8cce8eb19d893d9a47975dd19039a0 bug fix.
+#
+# Before the fix, there were scenarios in which pg_stat_monitor could lose
+# queries (thus wrong call count/stats) when transitioning to a new bucket.
+# 
+# The problem before the fix is described below:
+# 1. Say current active bucket number is 1.
+# 2. QueryID XYZ has call count (calls) = 4.
+# 3. QueryID also has a pending query (not yet finished).
+# 4. Bucket 1 timer expires, pg_stat_monitor moves to bucket 2.
+# 5. pg_stat_monitor moves only the pending QueryID XYZ to bucket 2.
+# 6. Remove QueryID XYZ from bucket 1 (all stats, calls=4, etc..).
+# 
+# Since only the pending QueryID XYZ was moved to bucket 2, all
+# previous statistics for the same QueryID would have been incorrectly
+# removed from the previous bucket (1).
+#
+# PG-291 fixes the problem, by keeping finished queries in the previous bucket
+# and moving only the pending query to the new bucket.
+#
+# This test works as follows:
+# 1. Set pg_stat_monitor bucket time to 14 seconds.
+# 2. Start PostgreSQL, reset pg_stat_monitor view.
+# 3. Execute "SELECT pg_sleep(5)" three times in a row.
+# It's expected that the first two queries execute and finish in the
+# first bucket, then the last query starts in the same bucket but is finished
+# in the next bucket.
+# We expect a total query count of 3 for this query, and it must exist in two
+# buckets. 
+
+use strict;
+use warnings;
+use PostgresNode;
+use Test::More;
+
+
+# Create new PostgreSQL node and do initdb
+my $node = PostgresNode->get_new_node('test');
+my $pgdata = $node->data_dir;
+$node->dump_info;
+$node->init;
+$node->append_conf('postgresql.conf', "shared_preload_libraries = 'pg_stat_monitor'");
+# Set bucket duration to 14 seconds so tests don't take too long.
+$node->append_conf('postgresql.conf', "pg_stat_monitor.pgsm_bucket_time = 14");
+
+# Start server
+my $rt_value = $node->start;
+ok($rt_value == 1, "Start Server");
+
+my ($cmdret, $stdout, $stderr) = $node->psql('postgres', 'CREATE EXTENSION pg_stat_monitor;', extra_params => ['-a']);
+ok($cmdret == 0, "Create PGSM Extension");
+
+($cmdret, $stdout, $stderr) = $node->psql('postgres', 'SELECT pg_stat_monitor_reset();', extra_params => ['-a', '-Pformat=aligned','-Ptuples_only=off']);
+ok($cmdret == 0, "Reset PGSM Extension");
+
+$node->psql('postgres', "SELECT pg_sleep(5)");
+$node->psql('postgres', "SELECT pg_sleep(5)");
+$node->psql('postgres', "SELECT pg_sleep(5)");
+
+($cmdret, $stdout, $stderr) = $node->psql('postgres', 'SELECT bucket, queryid, calls, query FROM pg_stat_monitor;', extra_params => ['-a', '-Pformat=aligned']);
+ok($cmdret == 0, "Query pg_stat_monitor view");
+
+sub trim { my $s = shift; $s =~ s/^\s+|\s+$//g; return $s };
+
+my $last_bucket = "";
+my $bucket_cnt = 0;
+my $calls = 0;
+
+my @lines = split /\n/, $stdout;
+
+foreach my $line(@lines) {
+    my @tokens = split /\|/, $line;
+    my $bucket = trim($tokens[0]);
+    my $queryid = trim($tokens[1]);
+    my $ncalls = trim($tokens[2]);
+    my $query = trim($tokens[3]);
+
+    if ($query =~ "SELECT pg_sleep") {
+        $calls += $ncalls;
+        if ($bucket_cnt == 0) {
+            $bucket_cnt += 1;
+            $last_bucket = $bucket;
+        } elsif ($bucket != $last_bucket) {
+            $bucket_cnt += 1;
+            $last_bucket = $bucket;
+        }
+    }
+}
+
+ok($calls == 3, "Check total query count is correct");
+ok($bucket_cnt == 2, "Check total bucket count is correct");
+
+# Stop the server
+$node->stop;
+# Done testing for this testcase file.
+done_testing();
+