v1-0002-Add-wal_fpi_bytes_-un-compressed-to-EXPLAIN-WAL.patch

From 1a1f7d972ef7be24e5adf76c2ae201d6f4b6e396 Mon Sep 17 00:00:00 2001
From: Shinya Kato <shinya11.kato@gmail.com>
Date: Sat, 18 Oct 2025 16:28:05 +0900
Subject: [PATCH v1 2/3] Add wal_fpi_bytes_[un]compressed to EXPLAIN (WAL)

---
 doc/src/sgml/ref/explain.sgml     |  4 +++-
 src/backend/commands/explain.c    | 14 +++++++++++++-
 src/backend/executor/instrument.c |  6 ++++++
 src/include/executor/instrument.h |  2 ++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml
index 6dda680aa0d..7a4eeb06b3e 100644
--- a/doc/src/sgml/ref/explain.sgml
+++ b/doc/src/sgml/ref/explain.sgml
@@ -241,7 +241,9 @@ ROLLBACK;
      <para>
       Include information on WAL record generation. Specifically, include the
       number of records, number of full page images (fpi), the amount of WAL
-      generated in bytes and the number of times the WAL buffers became full.
+      generated in bytes, the number of times the WAL buffers became full, the
+      amount of WAL fpi generated in bytes after compression, and the amount of
+      WAL fpi generated in bytes before compression.
       In text format, only non-zero values are printed.
       This parameter may only be used when <literal>ANALYZE</literal> is also
       enabled.  It defaults to <literal>FALSE</literal>.
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index e6edae0845c..4dcfaf08cca 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -4283,7 +4283,9 @@ show_wal_usage(ExplainState *es, const WalUsage *usage)
 	{
 		/* Show only positive counter values. */
 		if ((usage->wal_records > 0) || (usage->wal_fpi > 0) ||
-			(usage->wal_bytes > 0) || (usage->wal_buffers_full > 0))
+			(usage->wal_bytes > 0) || (usage->wal_buffers_full > 0) ||
+			(usage->wal_fpi_bytes_uncompressed > 0) ||
+			(usage->wal_fpi_bytes_compressed > 0))
 		{
 			ExplainIndentText(es);
 			appendStringInfoString(es->str, "WAL:");
@@ -4300,6 +4302,12 @@ show_wal_usage(ExplainState *es, const WalUsage *usage)
 			if (usage->wal_buffers_full > 0)
 				appendStringInfo(es->str, " buffers full=%" PRId64,
 								 usage->wal_buffers_full);
+			if (usage->wal_fpi_bytes_uncompressed > 0)
+				appendStringInfo(es->str, " fpi bytes uncompressed=%" PRIu64,
+								 usage->wal_fpi_bytes_uncompressed);
+			if (usage->wal_fpi_bytes_compressed > 0)
+				appendStringInfo(es->str, " fpi bytes compressed=%" PRIu64,
+								 usage->wal_fpi_bytes_compressed);
 			appendStringInfoChar(es->str, '\n');
 		}
 	}
@@ -4313,6 +4321,10 @@ show_wal_usage(ExplainState *es, const WalUsage *usage)
 								usage->wal_bytes, es);
 		ExplainPropertyInteger("WAL Buffers Full", NULL,
 							   usage->wal_buffers_full, es);
+		ExplainPropertyUInteger("WAL FPI Bytes Uncompressed", NULL,
+								usage->wal_fpi_bytes_uncompressed, es);
+		ExplainPropertyUInteger("WAL FPI Bytes Compressed", NULL,
+								usage->wal_fpi_bytes_compressed, es);
 	}
 }
 
diff --git a/src/backend/executor/instrument.c b/src/backend/executor/instrument.c
index 56e635f4700..1d11a001d22 100644
--- a/src/backend/executor/instrument.c
+++ b/src/backend/executor/instrument.c
@@ -281,6 +281,8 @@ WalUsageAdd(WalUsage *dst, WalUsage *add)
 	dst->wal_records += add->wal_records;
 	dst->wal_fpi += add->wal_fpi;
 	dst->wal_buffers_full += add->wal_buffers_full;
+	dst->wal_fpi_bytes_uncompressed += add->wal_fpi_bytes_uncompressed;
+	dst->wal_fpi_bytes_compressed += add->wal_fpi_bytes_compressed;
 }
 
 void
@@ -290,4 +292,8 @@ WalUsageAccumDiff(WalUsage *dst, const WalUsage *add, const WalUsage *sub)
 	dst->wal_records += add->wal_records - sub->wal_records;
 	dst->wal_fpi += add->wal_fpi - sub->wal_fpi;
 	dst->wal_buffers_full += add->wal_buffers_full - sub->wal_buffers_full;
+	dst->wal_fpi_bytes_uncompressed +=
+		add->wal_fpi_bytes_uncompressed - sub->wal_fpi_bytes_uncompressed;
+	dst->wal_fpi_bytes_compressed +=
+		add->wal_fpi_bytes_compressed - sub->wal_fpi_bytes_compressed;
 }
diff --git a/src/include/executor/instrument.h b/src/include/executor/instrument.h
index 03653ab6c6c..2cc9c1e2b88 100644
--- a/src/include/executor/instrument.h
+++ b/src/include/executor/instrument.h
@@ -54,6 +54,8 @@ typedef struct WalUsage
 	int64		wal_fpi;		/* # of WAL full page images produced */
 	uint64		wal_bytes;		/* size of WAL records produced */
 	int64		wal_buffers_full;	/* # of times the WAL buffers became full */
+	uint64		wal_fpi_bytes_uncompressed;	/* size of FPIs before compression */
+	uint64		wal_fpi_bytes_compressed;	/* size of FPIs after compression */
 } WalUsage;
 
 /* Flag bits included in InstrAlloc's instrument_options bitmask */
-- 
2.47.3