Index: ext/session/session3.test
==================================================================
--- ext/session/session3.test
+++ ext/session/session3.test
@@ -17,19 +17,19 @@
 source [file join [file dirname [info script]] session_common.tcl]
 source $testdir/tester.tcl
 
 set testprefix session3
 
+#-------------------------------------------------------------------------
 # These tests - session3-1.* - verify that the session module behaves
 # correctly when confronted with a schema mismatch when applying a 
 # changeset (in function sqlite3changeset_apply()).
 #
 #   session3-1.1.*: Table does not exist in target db.
 #   session3-1.2.*: Table has wrong number of columns in target db.
 #   session3-1.3.*: Table has wrong PK columns in target db.
 #
-
 db close
 sqlite3_shutdown
 test_sqlite3_log log
 sqlite3 db test.db
 
@@ -74,10 +74,100 @@
     INSERT INTO t1 VALUES(9, 10);
     INSERT INTO t1 VALUES(11, 12);
   }
   set ::log
 } {SQLITE_SCHEMA {sqlite3changeset_apply(): primary key mismatch for table t1}}
+
+#-------------------------------------------------------------------------
+# These tests - session3-2.* - verify that the session module behaves
+# correctly when the schema of an attached table is modified during the
+# session.
+#
+#   session3-2.1.*: Table is dropped midway through the session.
+#   session3-2.2.*: Table is dropped and recreated with a different # cols.
+#   session3-2.3.*: Table is dropped and recreated with a different PK.
+#
+# In all of these scenarios, the call to sqlite3session_changeset() will
+# return SQLITE_SCHEMA. Also:
+#   
+#   session3-2.4.*: Table is dropped and recreated with an identical schema.
+#                   In this case sqlite3session_changeset() returns SQLITE_OK.
+#
+
+do_test 2.1 {
+  execsql { CREATE TABLE t2(a, b PRIMARY KEY) }
+  sqlite3session S db main
+  S attach t2
+  execsql {
+    INSERT INTO t2 VALUES(1, 2);
+    DROP TABLE t2;
+  }
+  list [catch { S changeset } msg] $msg
+} {1 SQLITE_SCHEMA}
+
+do_test 2.2.1 {
+  S delete
+  sqlite3session S db main
+  execsql { CREATE TABLE t2(a, b PRIMARY KEY, c) }
+  S attach t2
+  execsql {
+    INSERT INTO t2 VALUES(1, 2, 3);
+    DROP TABLE t2;
+    CREATE TABLE t2(a, b PRIMARY KEY);
+  }
+  list [catch { S changeset } msg] $msg
+} {1 SQLITE_SCHEMA}
+
+do_test 2.2.2 {
+  S delete
+  sqlite3session S db main
+  execsql { 
+    DROP TABLE t2;
+    CREATE TABLE t2(a, b PRIMARY KEY, c);
+  }
+  S attach t2
+  execsql {
+    INSERT INTO t2 VALUES(1, 2, 3);
+    DROP TABLE t2;
+    CREATE TABLE t2(a, b PRIMARY KEY, c, d);
+  }
+  list [catch { S changeset } msg] $msg
+} {1 SQLITE_SCHEMA}
+
+do_test 2.3 {
+  S delete
+  sqlite3session S db main
+  execsql { 
+    DROP TABLE t2;
+    CREATE TABLE t2(a, b PRIMARY KEY);
+  }
+  S attach t2
+  execsql {
+    INSERT INTO t2 VALUES(1, 2);
+    DROP TABLE t2;
+    CREATE TABLE t2(a PRIMARY KEY, b, c);
+  }
+  list [catch { S changeset } msg] $msg
+} {1 SQLITE_SCHEMA}
+
+do_test 2.4 {
+  S delete
+  sqlite3session S db main
+  execsql { 
+    DROP TABLE t2;
+    CREATE TABLE t2(a, b PRIMARY KEY);
+  }
+  S attach t2
+  execsql {
+    INSERT INTO t2 VALUES(1, 2);
+    DROP TABLE t2;
+    CREATE TABLE t2(a, b PRIMARY KEY);
+  }
+  list [catch { S changeset } msg] $msg
+} {0 {}}
+
+S delete
 
 
 catch { db close }
 catch { db2 close }
 sqlite3_shutdown

Index: ext/session/sqlite3session.c
==================================================================
--- ext/session/sqlite3session.c
+++ ext/session/sqlite3session.c
@@ -1347,16 +1347,23 @@
   rc = pSession->rc;
 
   for(pTab=pSession->pTable; rc==SQLITE_OK && pTab; pTab=pTab->pNext){
     if( pTab->nEntry ){
       const char *zName = pTab->zName;
-      int nCol = pTab->nCol;      /* Local copy of member variable */
-      u8 *abPK = pTab->abPK;      /* Local copy of member variable */
+      int nCol;                   /* Number of columns in table */
+      u8 *abPK;                   /* Primary key array */
+      const char **azCol = 0;     /* Table columns */
       int i;                      /* Used to iterate through hash buckets */
       sqlite3_stmt *pSel = 0;     /* SELECT statement to query table pTab */
       int nRewind = buf.nBuf;     /* Initial size of write buffer */
       int nNoop;                  /* Size of buffer after writing tbl header */
+
+      /* Check the table schema is still Ok. */
+      rc = sessionTableInfo(db, pSession->zDb, zName, &nCol, 0, &azCol, &abPK);
+      if( !rc && (pTab->nCol!=nCol || memcmp(abPK, pTab->abPK, nCol)) ){
+        rc = SQLITE_SCHEMA;
+      }
 
       /* Write a table header */
       sessionAppendByte(&buf, 'T', &rc);
       sessionAppendVarint(&buf, nCol, &rc);
       sessionAppendBlob(&buf, pTab->abPK, nCol, &rc);
@@ -1363,11 +1370,11 @@
       sessionAppendBlob(&buf, (u8 *)zName, strlen(zName)+1, &rc);
 
       /* Build and compile a statement to execute: */
       if( rc==SQLITE_OK ){
         rc = sessionSelectStmt(
-            db, pSession->zDb, zName, nCol, pTab->azCol, abPK, &pSel);
+            db, pSession->zDb, zName, nCol, azCol, abPK, &pSel);
       }
 
       if( rc==SQLITE_OK && nCol!=sqlite3_column_count(pSel) ){
         rc = SQLITE_SCHEMA;
       }
@@ -1405,10 +1412,11 @@
 
       sqlite3_finalize(pSel);
       if( buf.nBuf==nNoop ){
         buf.nBuf = nRewind;
       }
+      sqlite3_free(azCol);
     }
   }
 
   if( rc==SQLITE_OK ){
     *pnChangeset = buf.nBuf;