#209 add variable to control table empty algorithm

storage/tokudb/ha_tokudb.cc

@@ -1732,7 +1732,7 @@ int ha_tokudb::initialize_share(
         init_auto_increment();
     }
 
-    if (THDVAR(thd, open_table_check_empty) && may_table_be_empty(txn)) {
+    if (may_table_be_empty(txn)) {
         share->try_table_lock = true;
     }
     else {
@@ -3215,6 +3215,10 @@ bool ha_tokudb::may_table_be_empty(DB_TXN *txn) {
     DBC* tmp_cursor = NULL;
     DB_TXN* tmp_txn = NULL;
 
+    const int empty_scan = THDVAR(ha_thd(), empty_scan);
+    if (empty_scan == TOKUDB_EMPTY_SCAN_DISABLED)
+        goto cleanup;
+
     if (txn == NULL) {
         error = txn_begin(db_env, 0, &tmp_txn, 0, ha_thd());
         if (error) {
@@ -3224,21 +3228,23 @@ bool ha_tokudb::may_table_be_empty(DB_TXN *txn) {
     }
 
     error = share->file->cursor(share->file, txn, &tmp_cursor, 0);
-    if (error) {
+    if (error)
         goto cleanup;
-    }
-    error = tmp_cursor->c_getf_next(tmp_cursor, 0, smart_dbt_do_nothing, NULL);
-    if (error == DB_NOTFOUND) {
+     
+    if (empty_scan == TOKUDB_EMPTY_SCAN_LR)
+        error = tmp_cursor->c_getf_next(tmp_cursor, 0, smart_dbt_do_nothing, NULL);
+    else
+        error = tmp_cursor->c_getf_prev(tmp_cursor, 0, smart_dbt_do_nothing, NULL);
+    if (error == DB_NOTFOUND)
         ret_val = true;
-    }
-    else {
+    else 
         ret_val = false;
-    }
     error = 0;
+
 cleanup:
     if (tmp_cursor) {
         int r = tmp_cursor->c_close(tmp_cursor);
-        assert(r==0);
+        assert(r == 0);
         tmp_cursor = NULL;
     }
     if (tmp_txn) {

storage/tokudb/hatoku_hton.cc

@@ -1390,7 +1390,7 @@ static struct st_mysql_sys_var *tokudb_system_variables[] = {
     MYSQL_SYSVAR(loader_memory_size),
     MYSQL_SYSVAR(hide_default_row_format),
     MYSQL_SYSVAR(killed_time),
-    MYSQL_SYSVAR(open_table_check_empty),
+    MYSQL_SYSVAR(empty_scan),
     NULL
 };
 

storage/tokudb/hatoku_hton.h

@@ -484,7 +484,31 @@ static int tokudb_killed_callback(void) {
     return thd->killed;
 }
 
-static MYSQL_THDVAR_BOOL(open_table_check_empty, 0, "Check if table is empty at first open", NULL /*check*/, NULL /*update*/, true /*default*/);
+enum {
+    TOKUDB_EMPTY_SCAN_DISABLED = 0,
+    TOKUDB_EMPTY_SCAN_LR = 1,
+    TOKUDB_EMPTY_SCAN_RL = 2,
+};
+
+static const char *tokudb_empty_scan_names[] = {
+    "disabled",
+    "lr",
+    "rl",
+    NullS
+};
+
+static TYPELIB tokudb_empty_scan_typelib = {
+    array_elements(tokudb_empty_scan_names) - 1,
+    "tokudb_empty_scan_typelib",
+    tokudb_empty_scan_names,
+    NULL
+};
+
+static MYSQL_THDVAR_ENUM(empty_scan,
+    PLUGIN_VAR_OPCMDARG,
+    "TokuDB algorithm to check if the table is empty when opened. ",
+    NULL, NULL, TOKUDB_EMPTY_SCAN_RL, &tokudb_empty_scan_typelib
+);
 
 extern HASH tokudb_open_tables;
 extern pthread_mutex_t tokudb_mutex;