InnoDB: Allow concurrent TRUNCATE and INSERT on a table. (Bug #8144)

innobase/include/rem0rec.ic:
  Improve formatting of comments
innobase/include/trx0trx.h:
  dict_operation: document the effect of setting the flag
innobase/row/row0mysql.c:
  Do not set the dict_operation flag. (Bug #8144)
  Allow MySQL to have open handles to the table being truncated.
sql/ha_innodb.cc:
  store_lock(): Do not weaken TL_WRITE locks taken by TRUNCATE TABLE.

innobase/include/rem0rec.ic

@@ -526,7 +526,7 @@ bits of a record.  (Only compact records have status bits.) */
 UNIV_INLINE
 ulint
 rec_get_info_and_status_bits(
-/*==============*/
+/*=========================*/
 			/* out: info bits */
 	rec_t*	rec,	/* in: physical record */
 	ibool	comp)	/* in: TRUE=compact page format */
@@ -550,7 +550,7 @@ bits of a record.  (Only compact records have status bits.) */
 UNIV_INLINE
 void
 rec_set_info_and_status_bits(
-/*==============*/
+/*=========================*/
 	rec_t*	rec,	/* in: physical record */
 	ibool	comp,	/* in: TRUE=compact page format */
 	ulint	bits)	/* in: info bits */

innobase/include/trx0trx.h

@@ -383,7 +383,9 @@ struct trx_struct{
 	dulint		commit_lsn;	/* lsn at the time of the commit */
 	ibool		dict_operation;	/* TRUE if the trx is used to create
 					a table, create an index, or drop a
-					table */
+					table.  This is a hint that the table
+					may need to be dropped in crash
+					recovery. */
 	dulint		table_id;	/* table id if the preceding field is
 					TRUE */
 	/*------------------------------*/

innobase/row/row0mysql.c

@@ -2561,17 +2561,6 @@ do not allow the TRUNCATE.  We also reserve the data dictionary latch. */
 		goto funct_exit;
 	}
 
-	if (table->n_mysql_handles_opened > 1) {
-		ut_print_timestamp(stderr);
-fputs("	 InnoDB: Warning: MySQL is trying to truncate table ", stderr);
-		ut_print_name(stderr, trx, table->name);
-		fputs("\n"
-"InnoDB: though there are still open handles to it.\n", stderr);
-		err = DB_ERROR;
-
-		goto funct_exit;
-	}
-
 	/* TODO: could we replace the counter n_foreign_key_checks_running
 	with lock checks on the table? Acquire here an exclusive lock on the
 	table, and rewrite lock0lock.c and the lock wait in srv0srv.c so that
@@ -2594,7 +2583,6 @@ fputs("	 InnoDB: Warning: MySQL is trying to truncate table ", stderr);
 
 	lock_reset_all_on_table(table);
 
-	trx->dict_operation = TRUE;
 	trx->table_id = table->id;
 
 	/* scan SYS_INDEXES for all indexes of the table */

sql/ha_innodb.cc

@@ -5787,11 +5787,12 @@ ha_innobase::store_lock(
 	if (lock_type != TL_IGNORE && lock.type == TL_UNLOCK) {
 
     		/* If we are not doing a LOCK TABLE or DISCARD/IMPORT
-		TABLESPACE, then allow multiple writers */
+		TABLESPACE or TRUNCATE TABLE, then allow multiple writers */
 
     		if ((lock_type >= TL_WRITE_CONCURRENT_INSERT &&
 	 	    lock_type <= TL_WRITE) && !thd->in_lock_tables
-		    && !thd->tablespace_op) {
+		    && !thd->tablespace_op
+		    && thd->lex->sql_command != SQLCOM_TRUNCATE) {
 
       			lock_type = TL_WRITE_ALLOW_WRITE;
       		}