Cleanup: Remove pointer indirection for trx_t::xid

The trx_t::xid is always allocated, so we might as well allocate it
directly in the trx_t object to improve the locality of reference.

storage/innobase/handler/ha_innodb.cc

@@ -4357,7 +4357,7 @@ innobase_commit_ordered_2(
 	/* If the transaction is not run in 2pc, we must assign wsrep
 	XID here in order to get it written in rollback segment. */
 	if (trx->is_wsrep()) {
-		thd_get_xid(thd, (MYSQL_XID*)trx->xid);
+		thd_get_xid(thd, &reinterpret_cast<MYSQL_XID&>(trx->xid));
 	}
 #endif /* WITH_WSREP */
 
@@ -4552,8 +4552,9 @@ innobase_rollback(
 	trx is being rolled back due to BF abort, clear XID in order
 	to avoid writing it to rollback segment out of order. The XID
 	will be reassigned when the transaction is replayed. */
-	if (trx->state != TRX_STATE_NOT_STARTED && wsrep_is_wsrep_xid(trx->xid)) {
-		trx->xid->null();
+	if (trx->state != TRX_STATE_NOT_STARTED
+	    && wsrep_is_wsrep_xid(&trx->xid)) {
+		trx->xid.null();
 	}
 #endif /* WITH_WSREP */
 	if (rollback_trx
@@ -16683,7 +16684,7 @@ innobase_xa_prepare(
 
 	DBUG_ASSERT(hton == innodb_hton_ptr);
 
-	thd_get_xid(thd, (MYSQL_XID*) trx->xid);
+	thd_get_xid(thd, &reinterpret_cast<MYSQL_XID&>(trx->xid));
 
 	if (!trx_is_registered_for_2pc(trx) && trx_is_started(trx)) {
 
@@ -16815,8 +16816,8 @@ int innobase_rollback_by_xid(handlerton* hton, XID* xid)
 		/* If a wsrep transaction is being rolled back during
 		the recovery, we must clear the xid in order to avoid
 		writing serialisation history for rolled back transaction. */
-		if (wsrep_is_wsrep_xid(trx->xid)) {
-			trx->xid->null();
+		if (wsrep_is_wsrep_xid(&trx->xid)) {
+			trx->xid.null();
 		}
 #endif /* WITH_WSREP */
 		int ret = innobase_rollback_trx(trx);
@@ -18312,7 +18313,7 @@ void lock_wait_wsrep_kill(trx_t *bf_trx, ulong thd_id, trx_id_t trx_id)
         default:
           break;
         case TRX_STATE_PREPARED:
-          if (!wsrep_is_wsrep_xid(vtrx->xid))
+          if (!wsrep_is_wsrep_xid(&vtrx->xid))
             break;
           /* fall through */
         case TRX_STATE_ACTIVE:

storage/innobase/include/trx0trx.h

@@ -859,7 +859,7 @@ struct trx_t : ilist_node<>
 	const char*	start_file;	/*!< Filename where it was started */
 #endif /* UNIV_DEBUG */
 
-	XID*		xid;		/*!< X/Open XA transaction
+	XID		xid;		/*!< X/Open XA transaction
 					identification to identify a
 					transaction branch */
 	trx_mod_tables_t mod_tables;	/*!< List of tables that were modified

storage/innobase/trx/trx0purge.cc

@@ -284,8 +284,8 @@ trx_purge_add_undo_to_history(const trx_t* trx, trx_undo_t*& undo, mtr_t* mtr)
 		  && srv_fast_shutdown));
 
 #ifdef	WITH_WSREP
-	if (wsrep_is_wsrep_xid(trx->xid)) {
-		trx_rseg_update_wsrep_checkpoint(rseg_header, trx->xid, mtr);
+	if (wsrep_is_wsrep_xid(&trx->xid)) {
+		trx_rseg_update_wsrep_checkpoint(rseg_header, &trx->xid, mtr);
 	}
 #endif
 

storage/innobase/trx/trx0trx.cc

@@ -178,8 +178,6 @@ struct TrxFactory {
 
 		trx->dict_operation_lock_mode = 0;
 
-		trx->xid = UT_NEW_NOKEY(xid_t());
-
 		trx->detailed_error = reinterpret_cast<char*>(
 			ut_zalloc_nokey(MAX_DETAILED_ERROR_LEN));
 
@@ -231,7 +229,6 @@ struct TrxFactory {
 		ut_a(UT_LIST_GET_LEN(trx->lock.trx_locks) == 0);
 		ut_ad(UT_LIST_GET_LEN(trx->lock.evicted_tables) == 0);
 
-		UT_DELETE(trx->xid);
 		ut_free(trx->detailed_error);
 
 		trx->mutex_destroy();
@@ -675,7 +672,7 @@ static void trx_resurrect(trx_undo_t *undo, trx_rseg_t *rseg,
     this trx_ref_count w/o mutex protection.
   */
   trx->rsegs.m_redo.rseg->acquire();
-  *trx->xid= undo->xid;
+  trx->xid= undo->xid;
   trx->id= undo->trx_id;
   trx->is_recovered= true;
   trx->start_time= start_time;
@@ -913,7 +910,7 @@ trx_start_low(
 	}
 
 #ifdef WITH_WSREP
-	trx->xid->null();
+	trx->xid.null();
 #endif /* WITH_WSREP */
 
 	ut_a(ib_vector_is_empty(trx->autoinc_locks));
@@ -1347,7 +1344,7 @@ inline void trx_t::commit_in_memory(const mtr_t *mtr)
     serialize all commits and prevent a group of transactions from
     gathering. */
 
-    commit_lsn= undo_no || !xid->is_null() ? mtr->commit_lsn() : 0;
+    commit_lsn= undo_no || !xid.is_null() ? mtr->commit_lsn() : 0;
     if (!commit_lsn)
       /* Nothing to be done. */;
     else if (flush_log_later)
@@ -1922,7 +1919,7 @@ static my_bool trx_recover_for_mysql_callback(rw_trx_hash_element_t *element,
                    << " in prepared state after recovery";
         ib::info() << "Transaction contains changes to " << trx->undo_no
                    << " rows";
-        xid= *trx->xid;
+        xid= trx->xid;
       }
     }
   }
@@ -1997,16 +1994,16 @@ static my_bool trx_get_trx_by_xid_callback(rw_trx_hash_element_t *element,
     if (trx->is_recovered &&
 	(trx_state_eq(trx, TRX_STATE_PREPARED) ||
 	 trx_state_eq(trx, TRX_STATE_PREPARED_RECOVERED)) &&
-        arg->xid->eq(reinterpret_cast<XID*>(trx->xid)))
+        arg->xid->eq(&trx->xid))
     {
 #ifdef WITH_WSREP
       /* The commit of a prepared recovered Galera
       transaction needs a valid trx->xid for
       invoking trx_sys_update_wsrep_checkpoint(). */
-      if (!wsrep_is_wsrep_xid(trx->xid))
+      if (!wsrep_is_wsrep_xid(&trx->xid))
 #endif /* WITH_WSREP */
       /* Invalidate the XID, so that subsequent calls will not find it. */
-      trx->xid->null();
+      trx->xid.null();
       arg->trx= trx;
       found= 1;
     }

storage/innobase/trx/trx0undo.cc

@@ -1051,7 +1051,7 @@ trx_undo_create(trx_t* trx, trx_rseg_t* rseg, trx_undo_t** undo,
 
 	uint16_t offset = trx_undo_header_create(block, trx->id, mtr);
 
-	*undo = trx_undo_mem_create(rseg, id, trx->id, trx->xid,
+	*undo = trx_undo_mem_create(rseg, id, trx->id, &trx->xid,
 				    block->page.id().page_no(), offset);
 	if (*undo == NULL) {
 		*err = DB_OUT_OF_MEMORY;
@@ -1109,7 +1109,7 @@ trx_undo_reuse_cached(trx_t* trx, trx_rseg_t* rseg, trx_undo_t** pundo,
 
 	uint16_t offset = trx_undo_header_create(block, trx->id, mtr);
 
-	trx_undo_mem_init_for_reuse(undo, trx->id, trx->xid, offset);
+	trx_undo_mem_init_for_reuse(undo, trx->id, &trx->xid, offset);
 
 	if (rseg != trx->rsegs.m_redo.rseg) {
 		return block;
@@ -1277,7 +1277,7 @@ void trx_undo_set_state_at_prepare(trx_t *trx, trx_undo_t *undo, bool rollback,
 	/*------------------------------*/
 	ut_ad(undo->state == TRX_UNDO_ACTIVE);
 	undo->state = TRX_UNDO_PREPARED;
-	undo->xid   = *trx->xid;
+	undo->xid   = trx->xid;
 	/*------------------------------*/
 
 	mtr->write<2>(*block, TRX_UNDO_SEG_HDR + TRX_UNDO_STATE + block->frame,