Avoid loading the entire record into memory for an sqlite3_preupdate_old() call that retrieves an IPK value.

FossilOrigin-Name: 7f4de43733200beeb3ff0a70d51bbc68f5331895698ea95a82741cfd7bb66834

ext/session/sessionblob.test

@@ -0,0 +1,55 @@
+# 2024 November 04
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+
+if {![info exists testdir]} {
+  set testdir [file join [file dirname [info script]] .. .. test]
+} 
+source [file join [file dirname [info script]] session_common.tcl]
+source $testdir/tester.tcl
+ifcapable !session {finish_test; return}
+
+if {$::tcl_platform(pointerSize)<8} {
+  finish_test
+  return
+}
+
+set testprefix sessionblob
+
+forcedelete test.db2
+sqlite3 db2 test.db2
+
+set NBLOB 2000000
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(a INTEGER PRIMARY KEY, b);
+  INSERT INTO t1 VALUES(123, zeroblob($NBLOB));
+}
+
+do_test 1.1 {
+  sqlite3session S db main
+  S attach t1
+} {}
+
+set b2 [string repeat x 1000]
+do_test 1.2 {
+  set ::blob [db incrblob t1 b 123]
+  for {set ii 0} {$ii < $NBLOB} {incr ii [string length $b2]} {
+    seek $::blob $ii
+    puts -nonewline $::blob $b2
+  }
+  close $::blob
+} {}
+
+S delete
+
+finish_test
+