Add SQL functions to monitor the directory contents of replication slots

This commit adds a set of functions able to look at the contents of
various paths related to replication slots:
- pg_ls_logicalsnapdir, for pg_logical/snapshots/
- pg_ls_logicalmapdir, for pg_logical/mappings/
- pg_ls_replslotdir, for pg_replslot/<slot_name>/

These are intended to be used by monitoring tools.  Unlike pg_ls_dir(),
execution permission can be granted to non-superusers.  Roles members of
pg_monitor gain have access to those functions.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Justin Pryzby
Discussion: https://postgr.es/m/CALj2ACWsfizZjMN6bzzdxOk1ADQQeSw8HhEjhmVXn_Pu+7VzLw@mail.gmail.com

1 files changed, 44 insertions, 0 deletions

diff --git a/src/backend/utils/adt/genfile.c b/src/backend/utils/adt/genfile.c
index c436d9318b6..027ed864001 100644
--- a/src/backend/utils/adt/genfile.c
+++ b/src/backend/utils/adt/genfile.c
@@ -29,6 +29,7 @@
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "postmaster/syslogger.h"
+#include "replication/slot.h"
 #include "storage/fd.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
@@ -720,3 +721,46 @@ pg_ls_archive_statusdir(PG_FUNCTION_ARGS)
 {
 	return pg_ls_dir_files(fcinfo, XLOGDIR "/archive_status", true);
 }
+
+/*
+ * Function to return the list of files in the pg_logical/snapshots directory.
+ */
+Datum
+pg_ls_logicalsnapdir(PG_FUNCTION_ARGS)
+{
+	return pg_ls_dir_files(fcinfo, "pg_logical/snapshots", false);
+}
+
+/*
+ * Function to return the list of files in the pg_logical/mappings directory.
+ */
+Datum
+pg_ls_logicalmapdir(PG_FUNCTION_ARGS)
+{
+	return pg_ls_dir_files(fcinfo, "pg_logical/mappings", false);
+}
+
+/*
+ * Function to return the list of files in the pg_replslot/<replication_slot>
+ * directory.
+ */
+Datum
+pg_ls_replslotdir(PG_FUNCTION_ARGS)
+{
+	text	   *slotname_t;
+	char		path[MAXPGPATH];
+	char	   *slotname;
+
+	slotname_t = PG_GETARG_TEXT_PP(0);
+
+	slotname = text_to_cstring(slotname_t);
+
+	if (!SearchNamedReplicationSlot(slotname, true))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("replication slot \"%s\" does not exist",
+						slotname)));
+
+	snprintf(path, sizeof(path), "pg_replslot/%s", slotname);
+	return pg_ls_dir_files(fcinfo, path, false);
+}