From 10076ae9e497cf59407d0f47ce7fee77762b82aa Mon Sep 17 00:00:00 2001
From: alterego655 <824662526@qq.com>
Date: Tue, 22 Sep 2026 16:53:25 +0800
Subject: [PATCH v1 1/2] Expose the WAL insertion end position to SQL

Add pg_current_wal_insert_end_lsn(), backed by GetXLogInsertEndRecPtr().
It reports the end of reserved WAL space without including the next
page header when that space ends at a page or segment boundary.

Document that the position is server-wide and may include concurrent
insertions that have not finished; reading it does not write or flush WAL.
Keep pg_current_wal_insert_lsn() unchanged.
---
 doc/src/sgml/func/func-admin.sgml      | 28 ++++++++++++++++++++++++++
 src/backend/access/transam/xlogfuncs.c | 22 ++++++++++++++++++++
 src/include/catalog/pg_proc.dat        |  4 ++++
 3 files changed, 54 insertions(+)

diff --git a/doc/src/sgml/func/func-admin.sgml b/doc/src/sgml/func/func-admin.sgml
index 64b0e7bb972..b325fed4ca7 100644
--- a/doc/src/sgml/func/func-admin.sgml
+++ b/doc/src/sgml/func/func-admin.sgml
@@ -376,6 +376,20 @@ LOG:  Grand total: 1651920 bytes in 201 blocks; 622360 free (88 chunks); 1029560
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_current_wal_insert_end_lsn</primary>
+        </indexterm>
+        <function>pg_current_wal_insert_end_lsn</function> ()
+        <returnvalue>pg_lsn</returnvalue>
+       </para>
+       <para>
+        Returns the end of the write-ahead log space currently reserved for
+        insertion (see notes below).
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
@@ -598,6 +612,20 @@ LOG:  Grand total: 1651920 bytes in 201 blocks; 622360 free (88 chunks); 1029560
     not require superuser permissions.
    </para>
 
+   <para>
+    <function>pg_current_wal_insert_end_lsn</function> reports the same
+    reservation position as <function>pg_current_wal_insert_lsn</function>,
+    but represents it as a record end.  If the reserved space ends exactly
+    at a WAL page boundary, it returns that boundary, whereas
+    <function>pg_current_wal_insert_lsn</function> returns the next insertion
+    address, after the following page's header.  Otherwise, the two positions
+    are the same.  Neither function waits for concurrent WAL insertions to
+    finish or causes WAL to be written or flushed.  Both positions are
+    server-wide, rather than specific to the calling session or transaction,
+    and neither function can be executed during recovery.  Both are read-only
+    operations and do not require superuser permissions.
+   </para>
+
    <para>
     You can use <function>pg_walfile_name_offset</function> to extract the
     corresponding write-ahead log file name and byte offset from
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 1f52bf7b420..d8ae8cdfee0 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -337,6 +337,28 @@ pg_current_wal_insert_lsn(PG_FUNCTION_ARGS)
 	PG_RETURN_LSN(current_recptr);
 }
 
+/*
+ * Report the end of the WAL space reserved for insertion.
+ *
+ * Unlike pg_current_wal_insert_lsn(), this does not include the following
+ * page header when the reserved space ends at a WAL page boundary.
+ */
+Datum
+pg_current_wal_insert_end_lsn(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	current_recptr;
+
+	if (RecoveryInProgress())
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("recovery is in progress"),
+				 errhint("WAL control functions cannot be executed during recovery.")));
+
+	current_recptr = GetXLogInsertEndRecPtr();
+
+	PG_RETURN_LSN(current_recptr);
+}
+
 /*
  * Report the current WAL flush location (same format as pg_backup_start etc)
  *
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index f46427258e3..955aa17e3ec 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -6882,6 +6882,10 @@
   proname => 'pg_current_wal_insert_lsn', provolatile => 'v',
   prorettype => 'pg_lsn', proargtypes => '',
   prosrc => 'pg_current_wal_insert_lsn' },
+{ oid => '8922', descr => 'current wal insertion end location',
+  proname => 'pg_current_wal_insert_end_lsn', provolatile => 'v',
+  prorettype => 'pg_lsn', proargtypes => '',
+  prosrc => 'pg_current_wal_insert_end_lsn' },
 { oid => '3330', descr => 'current wal flush location',
   proname => 'pg_current_wal_flush_lsn', provolatile => 'v',
   prorettype => 'pg_lsn', proargtypes => '',
-- 
2.51.0