Migrate pg_locks to collector package (#817)

Migrate the `pg_locks_count` query from `main` to the `collector`
package.

Signed-off-by: SuperQ <superq@gmail.com>

cmd/postgres_exporter/postgres_exporter.go

@@ -176,15 +176,6 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		true,
 		0,
 	},
-	"pg_locks": {
-		map[string]ColumnMapping{
-			"datname": {LABEL, "Name of this database", nil, nil},
-			"mode":    {LABEL, "Type of Lock", nil, nil},
-			"count":   {GAUGE, "Number of locks", nil, nil},
-		},
-		true,
-		0,
-	},
 	"pg_stat_replication": {
 		map[string]ColumnMapping{
 			"procpid":                  {DISCARD, "Process ID of a WAL sender process", nil, semver.MustParseRange("<9.2.0")},

cmd/postgres_exporter/queries.go

@@ -46,31 +46,6 @@ type OverrideQuery struct {
 // Overriding queries for namespaces above.
 // TODO: validate this is a closed set in tests, and there are no overlaps
 var queryOverrides = map[string][]OverrideQuery{
-	"pg_locks": {
-		{
-			semver.MustParseRange(">0.0.0"),
-			`SELECT pg_database.datname,tmp.mode,COALESCE(count,0) as count
-			FROM
-				(
-				  VALUES ('accesssharelock'),
-				         ('rowsharelock'),
-				         ('rowexclusivelock'),
-				         ('shareupdateexclusivelock'),
-				         ('sharelock'),
-				         ('sharerowexclusivelock'),
-				         ('exclusivelock'),
-				         ('accessexclusivelock'),
-					 ('sireadlock')
-				) AS tmp(mode) CROSS JOIN pg_database
-			LEFT JOIN
-			  (SELECT database, lower(mode) AS mode,count(*) AS count
-			  FROM pg_locks WHERE database IS NOT NULL
-			  GROUP BY database, lower(mode)
-			) AS tmp2
-			ON tmp.mode=tmp2.mode and pg_database.oid = tmp2.database ORDER BY 1`,
-		},
-	},
-
 	"pg_stat_replication": {
 		{
 			semver.MustParseRange(">=10.0.0"),