From 8e05639dbf6def383da7b138e28cf930ac506647 Mon Sep 17 00:00:00 2001
From: Konstantin Knizhnik <knizhnik@garret.ru>
Date: Sat, 17 May 2025 22:06:59 +0300
Subject: [PATCH] Invalidate LFC after unlogged build (#11951)

## Problem


See https://neondb.slack.com/archives/C04DGM6SMTM/p1747391617951239

LFC is not always properly updated during unlogged build so it can
contain stale content.

## Summary of changes

Invalidate LFC content at the end of unlogged build

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
---
 pgxn/neon/file_cache.c     | 38 ++++++++++++++++++++++++++++++++++++++
 pgxn/neon/file_cache.h     |  1 +
 pgxn/neon/pagestore_smgr.c | 19 ++-----------------
 3 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/pgxn/neon/file_cache.c b/pgxn/neon/file_cache.c
index ecc55bb540..176fd9643f 100644
--- a/pgxn/neon/file_cache.c
+++ b/pgxn/neon/file_cache.c
@@ -936,6 +936,44 @@ lfc_prewarm_main(Datum main_arg)
 	lfc_ctl->prewarm_workers[worker_id].completed = GetCurrentTimestamp();
 }
 
+void
+lfc_invalidate(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber nblocks)
+{
+	BufferTag	tag;
+	FileCacheEntry *entry;
+	uint32		hash;
+
+	if (lfc_maybe_disabled())	/* fast exit if file cache is disabled */
+		return;
+
+	CopyNRelFileInfoToBufTag(tag, rinfo);
+	tag.forkNum = forkNum;
+
+	CriticalAssert(BufTagGetRelNumber(&tag) != InvalidRelFileNumber);
+
+	LWLockAcquire(lfc_lock, LW_EXCLUSIVE);
+	if (LFC_ENABLED())
+	{
+		for (BlockNumber blkno = 0; blkno < nblocks; blkno += lfc_blocks_per_chunk)
+		{
+			tag.blockNum = blkno;
+			hash = get_hash_value(lfc_hash, &tag);
+			entry = hash_search_with_hash_value(lfc_hash, &tag, hash, HASH_FIND, NULL);
+			if (entry != NULL)
+			{
+				for (int i = 0; i < lfc_blocks_per_chunk; i++)
+				{
+					if (GET_STATE(entry, i) == AVAILABLE)
+					{
+						lfc_ctl->used_pages -= 1;
+						SET_STATE(entry, i, UNAVAILABLE);
+					}
+				}
+			}
+		}
+	}
+	LWLockRelease(lfc_lock);
+}
 
 /*
  * Check if page is present in the cache.
diff --git a/pgxn/neon/file_cache.h b/pgxn/neon/file_cache.h
index c7b6b09f72..d5ac55d5ba 100644
--- a/pgxn/neon/file_cache.h
+++ b/pgxn/neon/file_cache.h
@@ -28,6 +28,7 @@ typedef struct FileCacheState
 extern bool lfc_store_prefetch_result;
 
 /* functions for local file cache */
+extern void lfc_invalidate(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber nblocks);
 extern void lfc_writev(NRelFileInfo rinfo, ForkNumber forkNum,
 					   BlockNumber blkno, const void *const *buffers,
 					   BlockNumber nblocks);
diff --git a/pgxn/neon/pagestore_smgr.c b/pgxn/neon/pagestore_smgr.c
index 31e47db7d7..5558a903e2 100644
--- a/pgxn/neon/pagestore_smgr.c
+++ b/pgxn/neon/pagestore_smgr.c
@@ -919,9 +919,6 @@ neon_extend(SMgrRelation reln, ForkNumber forkNum, BlockNumber blkno,
 		case RELPERSISTENCE_TEMP:
 		case RELPERSISTENCE_UNLOGGED:
 			mdextend(reln, forkNum, blkno, buffer, skipFsync);
-			/* Update LFC in case of unlogged index build */
-			if (reln == unlogged_build_rel && unlogged_build_phase == UNLOGGED_BUILD_PHASE_2)
-				lfc_write(InfoFromSMgrRel(reln), forkNum, blkno, buffer);
 			return;
 
 		default:
@@ -1010,14 +1007,6 @@ neon_zeroextend(SMgrRelation reln, ForkNumber forkNum, BlockNumber blocknum,
 		case RELPERSISTENCE_TEMP:
 		case RELPERSISTENCE_UNLOGGED:
 			mdzeroextend(reln, forkNum, blocknum, nblocks, skipFsync);
-			/* Update LFC in case of unlogged index build */
-			if (reln == unlogged_build_rel && unlogged_build_phase == UNLOGGED_BUILD_PHASE_2)
-			{
-				for (int i = 0; i < nblocks; i++)
-				{
-					lfc_write(InfoFromSMgrRel(reln), forkNum, blocknum + i, buffer.data);
-				}
-			}
 			return;
 
 		default:
@@ -1617,9 +1606,6 @@ neon_write(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, const vo
 			#else
 			mdwrite(reln, forknum, blocknum, buffer, skipFsync);
 			#endif
-			/* Update LFC in case of unlogged index build */
-			if (reln == unlogged_build_rel && unlogged_build_phase == UNLOGGED_BUILD_PHASE_2)
-				lfc_write(InfoFromSMgrRel(reln), forknum, blocknum, buffer);
 			return;
 		default:
 			neon_log(ERROR, "unknown relpersistence '%c'", reln->smgr_relpersistence);
@@ -1685,9 +1671,6 @@ neon_writev(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
 		case RELPERSISTENCE_TEMP:
 		case RELPERSISTENCE_UNLOGGED:
 			mdwritev(reln, forknum, blkno, buffers, nblocks, skipFsync);
-			/* Update LFC in case of unlogged index build */
-			if (reln == unlogged_build_rel && unlogged_build_phase == UNLOGGED_BUILD_PHASE_2)
-				lfc_writev(InfoFromSMgrRel(reln), forknum, blkno, buffers, nblocks);
 			return;
 		default:
 			neon_log(ERROR, "unknown relpersistence '%c'", reln->smgr_relpersistence);
@@ -2083,6 +2066,8 @@ neon_end_unlogged_build(SMgrRelation reln)
 				 forknum);
 
 			forget_cached_relsize(InfoFromNInfoB(rinfob), forknum);
+			lfc_invalidate(InfoFromNInfoB(rinfob), forknum, nblocks);
+
 			mdclose(reln, forknum);
 #ifndef DEBUG_COMPARE_LOCAL
 			/* use isRedo == true, so that we drop it immediately */