Snapshot can use read-only transaction optimization of InnoDB after 5.6

[kinoyasu]

If the transactd doesn't set session variables of THD by users, snapshot (readonly transaction?) of the transactd can use read only transacion explicitly. InnoDB can optimize (skip useless processes for read-only transaction) for the snapshot.

--- transactd_orig_2.2.0/source/bzs/db/engine/mysql/database.cpp        2015-01-18 00:05:52.000000000 +0900
+++ mysql-5.6.23_td_test/plugin/transactd/source/bzs/db/engine/mysql/database.cpp       2015-02-18 19:25:05.133893783 +0900
@@ -304,14 +304,15 @@ void database::use() const

 void database::prebuildIsoratinMode()
 {
-    cp_thd_set_read_only(m_thd);
     if (m_inTransaction)
     {
+       cp_thd_set_read_only(m_thd, false);
         m_thd->tx_isolation = m_iso;
         m_thd->in_lock_tables = 1;// WITH LOCK
     }
     else if(m_inSnapshot)
     {
+       cp_thd_set_read_only(m_thd, true);
         if (m_iso)
         {
             m_thd->in_lock_tables = 1;// WITH LOCK
@@ -320,7 +321,10 @@ void database::prebuildIsoratinMode()
             m_thd->tx_isolation = ISO_REPEATABLE_READ;
     }
     else
+    {
+        cp_thd_set_read_only(m_thd, false);
         m_thd->tx_isolation = (enum_tx_isolation)m_thd->variables.tx_isolation;
+    }
 }

 void database::prebuildExclusieLockMode(table* tb)
--- transactd_orig_2.2.0/source/bzs/db/engine/mysql/mysqlInternal.h     2015-01-13 20:42:52.000000000 +0900
+++ mysql-5.6.23_td_test/plugin/transactd/source/bzs/db/engine/mysql/mysqlInternal.h    2015-02-18 19:24:17.364897009 +0900
@@ -173,7 +173,7 @@ inline void cp_restore_globals(THD* thd)
     my_pthread_setspecific_ptr(THR_MALLOC, 0);
 }

-inline void cp_thd_set_read_only(THD* thd)
+inline void cp_thd_set_read_only(THD* thd, bool read_only)
 {
     ;
 }
@@ -216,14 +216,14 @@ inline void cp_restore_globals(THD* thd)
     thd->restore_globals();
 }

-inline void cp_thd_set_read_only(THD* thd)
+inline void cp_thd_set_read_only(THD* thd, bool read_only)
 {
-    thd->tx_read_only = (thd->variables.tx_read_only != 0);
+    thd->tx_read_only = read_only;
 }

 inline bool cp_thd_get_read_only(THD* thd)
 {
-    return (thd->variables.tx_read_only != 0);
+    return (thd->tx_read_only);
 }

 inline bool cp_open_table(THD* thd, TABLE_LIST* tables,

[bizstation]

We have confirmed that a part of current source code is useless because thd->variables.tx_read_only does not change. I fixed it almost according to your patch.

Thank you for your advice.