Downgrade expert mode queries to blocksql

db/fdb_bend_sql.c

@@ -608,6 +608,7 @@ _fdb_svc_cursor_start(BtCursor *pCur, sqlclntstate *clnt, char *tblname,
     pCur->numblobs = get_schema_blob_count(pCur->db, ".ONDISK");
 
     if (need_bdbcursor) {
+        assert(clnt->dbtran.mode != TRANLEVEL_MODSNAP || clnt->modsnap_in_progress);
         pCur->bdbcur = bdb_cursor_open(
             pCur->db->handle, clnt->dbtran.cursor_tran,
             clnt->dbtran.shadow_tran, pCur->ixnum,

db/osqlshadtbl.c

@@ -2243,6 +2243,7 @@ static int insert_record_indexes(BtCursor *pCur, struct sql_thread *thd,
             }
         }
 
+        assert(thd->clnt->dbtran.mode != TRANLEVEL_MODSNAP || thd->clnt->modsnap_in_progress);
         tmpcur = bdb_cursor_open(
             pCur->db->handle, thd->clnt->dbtran.cursor_tran,
             thd->clnt->dbtran.shadow_tran, ix, BDB_OPEN_SHAD,
@@ -2349,6 +2350,7 @@ static int delete_record_indexes(BtCursor *pCur, char *pdta, int dtasize,
         }
         memcpy(&key[db->ix_keylen[ix]], &genid, sizeof(genid));
 
+        assert(thd->clnt->dbtran.mode != TRANLEVEL_MODSNAP || thd->clnt->modsnap_in_progress);
         tmpcur = bdb_cursor_open(
             db->handle, thd->clnt->dbtran.cursor_tran,
             thd->clnt->dbtran.shadow_tran, ix, BDB_OPEN_SHAD,

db/sqlglue.c

@@ -8449,6 +8449,7 @@ sqlite3BtreeCursor_cursor(Btree *pBt,      /* The btree */
     } else {
         open_type = BDB_OPEN_REAL;
     }
+    assert(clnt->dbtran.mode != TRANLEVEL_MODSNAP || clnt->modsnap_in_progress);
     cur->bdbcur = bdb_cursor_open(
         cur->db->handle, clnt->dbtran.cursor_tran, shadow_tran, cur->ixnum,
         open_type, (clnt->dbtran.mode == TRANLEVEL_SOSQL)

db/sqlinterfaces.c

@@ -3634,6 +3634,14 @@ static void handle_expert_query(struct sqlthdstate *thd,
     int rc;
     char *zErr = 0;
 
+    if (clnt->dbtran.mode == TRANLEVEL_MODSNAP) {
+        if (clnt->modsnap_in_progress) {
+            clear_modsnap_state(clnt);
+        }
+        logmsg(LOGMSG_WARN, "%s: Downgrading to blocksql for expert mode query\n", __func__);
+        clnt->dbtran.mode = TRANLEVEL_SOSQL;
+    }
+
     *outrc = 0;
     rdlock_schema_lk();
     rc = sqlengine_prepare_engine(thd, clnt, PREPARE_RECREATE);

tests/comdb2expert.test/snapshot.testopts

@@ -0,0 +1,2 @@
+sql_tranlevel_default snapshot
+enable_snapshot_isolation