From 8ca4540e2de3fbf670c4f30dfb6107a6ec8f17dd Mon Sep 17 00:00:00 2001
From: Tim <tim@example.com>
Date: Fri, 22 May 2026 15:34:38 -0700
Subject: [PATCH] Optimize variable-size single row replacements

---
 src/prolly_mutate.c   | 14 +++++++++-----
 test/invariant_test.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/src/prolly_mutate.c b/src/prolly_mutate.c
index d1df20c837..4cf6b81830 100644
--- a/src/prolly_mutate.c
+++ b/src/prolly_mutate.c
@@ -663,13 +663,11 @@ static int tryInsertOrReplaceSingleNoRechunk(ProllyMutator *pMut){
     const u8 *pOldVal;
     int nOldVal;
     ProllyNodeBuilder b;
+    int sameSize;
     int i;
 
     prollyNodeValue(pLeaf, idx, &pOldVal, &nOldVal);
-    if( nOldVal!=pEdit->nVal ){
-      prollyCursorClose(&cur);
-      return SQLITE_NOTFOUND;
-    }
+    sameSize = (nOldVal==pEdit->nVal);
 
     prollyNodeBuilderInit(&b, 0, pMut->flags);
     for(i=0; i<(int)pLeaf->nItems; i++){
@@ -685,7 +683,13 @@ static int tryInsertOrReplaceSingleNoRechunk(ProllyMutator *pMut){
         return rc;
       }
     }
-    rc = writeBuilderNode(pMut->pStore, &b, &childHash);
+    if( sameSize ){
+      rc = writeBuilderNode(pMut->pStore, &b, &childHash);
+    }else{
+      rc = finishAndWriteBuilderNode(pMut->pStore, &b,
+                                     !cursorLeafIsRightmost(&cur),
+                                     &childHash);
+    }
     prollyNodeBuilderFree(&b);
     if( rc!=SQLITE_OK ){
       prollyCursorClose(&cur);
diff --git a/test/invariant_test.c b/test/invariant_test.c
index f8159609c0..75a98d58a5 100644
--- a/test/invariant_test.c
+++ b/test/invariant_test.c
@@ -959,6 +959,35 @@ static void test_single_row_mutation_fast_path(void){
   check("single_mutation_integrity",
     strcmp(queryScalarText(db, "PRAGMA integrity_check"), "ok")==0);
 
+  execSql(db, "CREATE TABLE tblob(id BLOB PRIMARY KEY, val TEXT, pad TEXT)");
+  execSql(db, "BEGIN");
+  for( i=1; i<=5000; i++ ){
+    char sql[256];
+    snprintf(sql, sizeof(sql),
+      "INSERT INTO tblob VALUES(x'%032x', 'row_%d', 'pad')", i, i);
+    execSql(db, sql);
+  }
+  execSql(db, "COMMIT");
+
+  execSql(db,
+    "UPDATE tblob SET val='short' WHERE id=x'000000000000000000000000000009c4'");
+  execSql(db,
+    "UPDATE tblob SET val='this replacement is intentionally longer' "
+    "WHERE id=x'00000000000000000000000000000d05'");
+
+  check("single_mutation_blob_count",
+    queryScalarInt(db, "SELECT count(*) FROM tblob")==5000);
+  check("single_mutation_blob_short",
+    strcmp(queryScalarText(db,
+      "SELECT val FROM tblob WHERE id=x'000000000000000000000000000009c4'"),
+      "short")==0);
+  check("single_mutation_blob_long",
+    strcmp(queryScalarText(db,
+      "SELECT val FROM tblob WHERE id=x'00000000000000000000000000000d05'"),
+      "this replacement is intentionally longer")==0);
+  check("single_mutation_blob_integrity",
+    strcmp(queryScalarText(db, "PRAGMA integrity_check"), "ok")==0);
+
   sqlite3_close(db);
   removeDb(dbpath);
 }