Add contrib/pg_walinspect.

Provides similar functionality to pg_waldump, but from a SQL interface
rather than a separate utility.

Author: Bharath Rupireddy
Reviewed-by: Greg Stark, Kyotaro Horiguchi, Andres Freund, Ashutosh Sharma, Nitin Jadhav, RKN Sai Krishna
Discussion: https://postgr.es/m/CALj2ACUGUYXsEQdKhEdsBzhGEyF3xggvLdD8C0VT72TNEfOiog%40mail.gmail.com

1 files changed, 33 insertions, 0 deletions

diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index bb2d3ec991c..b5d34c61e66 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -80,6 +80,10 @@ typedef struct xl_invalid_page
 
 static HTAB *invalid_page_tab = NULL;
 
+static int
+read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr,
+						  int reqLen, XLogRecPtr targetRecPtr,
+						  char *cur_page, bool wait_for_wal);
 
 /* Report a reference to an invalid page */
 static void
@@ -871,6 +875,31 @@ int
 read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
 					 int reqLen, XLogRecPtr targetRecPtr, char *cur_page)
 {
+	return read_local_xlog_page_guts(state, targetPagePtr, reqLen,
+									 targetRecPtr, cur_page, true);
+}
+
+/*
+ * Same as read_local_xlog_page except that it doesn't wait for future WAL
+ * to be available.
+ */
+int
+read_local_xlog_page_no_wait(XLogReaderState *state, XLogRecPtr targetPagePtr,
+							 int reqLen, XLogRecPtr targetRecPtr,
+							 char *cur_page)
+{
+	return read_local_xlog_page_guts(state, targetPagePtr, reqLen,
+									 targetRecPtr, cur_page, false);
+}
+
+/*
+ * Implementation of read_local_xlog_page and its no wait version.
+ */
+static int
+read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr,
+						  int reqLen, XLogRecPtr targetRecPtr,
+						  char *cur_page, bool wait_for_wal)
+{
 	XLogRecPtr	read_upto,
 				loc;
 	TimeLineID	tli;
@@ -925,6 +954,10 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
 			if (loc <= read_upto)
 				break;
 
+			/* If asked, let's not wait for future WAL. */
+			if (!wait_for_wal)
+				break;
+
 			CHECK_FOR_INTERRUPTS();
 			pg_usleep(1000L);
 		}