From 65a438d87af11f314c5c235cd9e51ebee1852e82 Mon Sep 17 00:00:00 2001 From: Dmitry Lenev Date: Thu, 9 Sep 2010 18:29:14 +0400 Subject: Fix for bug #55273 "FLUSH TABLE tm WITH READ LOCK for Merge table causes assert failure". Attempting to use FLUSH TABLE table_list WITH READ LOCK statement for a MERGE table led to an assertion failure if one of its children was not present in the list of tables to be flushed. The problem was not visible in non-debug builds. The assertion failure was caused by the fact that in such situations FLUSH TABLES table_list WITH READ LOCK implementation tried to use (e.g. lock) such child tables without acquiring metadata lock on them. This happened because when opening tables we assumed metadata locks on all tables were already acquired earlier during statement execution and a such assumption was false for MERGE children. This patch fixes the problem by ensuring at open_tables() time that we try to acquire metadata locks on all tables to be opened. For normal tables such requests are satisfied instantly since locks are already acquired for them. For MERGE children metadata locks are acquired in normal fashion. Note that FLUSH TABLES merge_table WITH READ LOCK will lock for read both the MERGE table and its children but will flush only the MERGE table. To flush children one has to mention them in table list explicitly. This is expected behavior and it is consistent with usage patterns for this statement (e.g. in mysqlhotcopy script). mysql-test/r/flush.result: Added test case for bug #55273 "FLUSH TABLE tm WITH READ LOCK for Merge table causes assert failure". mysql-test/t/flush.test: Added test case for bug #55273 "FLUSH TABLE tm WITH READ LOCK for Merge table causes assert failure". sql/sql_base.cc: Changed lock_table_names() to support newly introduced MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK flag. sql/sql_base.h: Introduced MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK flag for open_tables() and lock_table_names() which allows to skip acquiring of global and schema-scope locks when SNW, SNRW or X metadata locks are acquired. sql/sql_reload.cc: Changed "FLUSH TABLES table_list WITH READ LOCK" code not to cause assert about missing metadata locks when MERGE table is flushed without one of its underlying tables. To achieve this we no longer call open_and_lock_tables() with MYSQL_OPEN_HAS_MDL_LOCK flag so this function automatically acquires metadata locks on MERGE children if such lock has not been already acquired at earlier stage. Instead we call this function with MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK flag to suppress acquiring of global IX lock in order to keep FLUSH TABLES table_list WITH READ LOCK compatible with FLUSH TABLE WITH READ LOCK. Also changed implementation to use lock_table_names() function for pre-acquiring of metadata locks instead of custom code. To implement this change moved setting of open_type member for table list elements to parser. sql/sql_yacc.yy: Now we set acceptable type of table for FLUSH TABLES table_list WITH READ LOCK at parsing time instead of execution time. --- sql/sql_reload.cc | 42 +++++++++++++++++++++++------------------- 1 file changed, 23 insertions(+), 19 deletions(-) (limited to 'sql/sql_reload.cc') diff --git a/sql/sql_reload.cc b/sql/sql_reload.cc index bf38af78536..35f27408247 100644 --- a/sql/sql_reload.cc +++ b/sql/sql_reload.cc @@ -328,7 +328,6 @@ bool reload_acl_and_cache(THD *thd, unsigned long options, ------------------------------------- - you can't flush WITH READ LOCK a non-existent table - you can't flush WITH READ LOCK under LOCK TABLES - - currently incompatible with the GRL (@todo: fix) Effect on views and temporary tables. ------------------------------------ @@ -338,6 +337,13 @@ bool reload_acl_and_cache(THD *thd, unsigned long options, if there is a base table, it's used, otherwise ER_NO_SUCH_TABLE is returned. + Handling of MERGE tables + ------------------------ + For MERGE table this statement will open and lock child tables + for read (it is impossible to lock parent table without it). + Child tables won't be flushed unless they are explicitly present + in the statement's table list. + Implicit commit --------------- This statement causes an implicit commit before and @@ -354,7 +360,6 @@ bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables) { Lock_tables_prelocking_strategy lock_tables_prelocking_strategy; TABLE_LIST *table_list; - MDL_request_list mdl_requests; /* This is called from SQLCOM_FLUSH, the transaction has @@ -368,17 +373,13 @@ bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables) } /* - Acquire SNW locks on tables to be flushed. We can't use - lock_table_names() here as this call will also acquire global IX - and database-scope IX locks on the tables, and this will make + Acquire SNW locks on tables to be flushed. Don't acquire global + IX and database-scope IX locks on the tables as this will make this statement incompatible with FLUSH TABLES WITH READ LOCK. */ - for (table_list= all_tables; table_list; - table_list= table_list->next_global) - mdl_requests.push_front(&table_list->mdl_request); - - if (thd->mdl_context.acquire_locks(&mdl_requests, - thd->variables.lock_wait_timeout)) + if (lock_table_names(thd, all_tables, NULL, + thd->variables.lock_wait_timeout, + MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK)) goto error; DEBUG_SYNC(thd,"flush_tables_with_read_lock_after_acquire_locks"); @@ -390,21 +391,24 @@ bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables) tdc_remove_table(thd, TDC_RT_REMOVE_UNUSED, table_list->db, table_list->table_name, FALSE); - - /* Skip views and temporary tables. */ - table_list->required_type= FRMTYPE_TABLE; /* Don't try to flush views. */ - table_list->open_type= OT_BASE_ONLY; /* Ignore temporary tables. */ + /* Reset ticket to satisfy asserts in open_tables(). */ + table_list->mdl_request.ticket= NULL; } /* Before opening and locking tables the below call also waits for old shares to go away, so the fact that we don't pass MYSQL_LOCK_IGNORE_FLUSH flag to it is important. + Also we don't pass MYSQL_OPEN_HAS_MDL_LOCK flag as we want + to open underlying tables if merge table is flushed. + For underlying tables of the merge the below call has to + acquire SNW locks to ensure that they can be locked for + read without further waiting. */ - if (open_and_lock_tables(thd, all_tables, FALSE, - MYSQL_OPEN_HAS_MDL_LOCK, - &lock_tables_prelocking_strategy) || - thd->locked_tables_list.init_locked_tables(thd)) + if (open_and_lock_tables(thd, all_tables, FALSE, + MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK, + &lock_tables_prelocking_strategy) || + thd->locked_tables_list.init_locked_tables(thd)) { goto error; } -- cgit v1.2.1 From bafe24035dbf6d5452d7328ab45d6b43abe52d54 Mon Sep 17 00:00:00 2001 From: Jon Olav Hauglid Date: Mon, 7 Mar 2011 10:08:10 +0100 Subject: Bug #11764779 (former 57649) FLUSH TABLES under FLUSH TABLES WITH READ LOCK leads to assert failure. This assert was triggered if a statement tried up upgrade a metadata lock with an active FLUSH TABLE WITH READ LOCK. The assert checks that the connection already holds a global intention exclusive metadata lock. However, FLUSH TABLE WITH READ LOCK does not acquire this lock in order to be compatible with FLUSH TABLES WITH READ LOCK. Therefore any metadata lock upgrade caused the assert to be triggered. This patch fixes the problem by preventing metadata lock upgrade if the connection has an active FLUSH TABLE WITH READ LOCK. ER_TABLE_NOT_LOCKED_FOR_WRITE will instead be reported to the client. Test case added to flush.test. --- sql/sql_reload.cc | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) (limited to 'sql/sql_reload.cc') diff --git a/sql/sql_reload.cc b/sql/sql_reload.cc index 0810459cb49..a09aa5511bd 100644 --- a/sql/sql_reload.cc +++ b/sql/sql_reload.cc @@ -1,4 +1,4 @@ -/* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved. +/* Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -220,12 +220,26 @@ bool reload_acl_and_cache(THD *thd, unsigned long options, if (tables) { for (TABLE_LIST *t= tables; t; t= t->next_local) - if (!find_table_for_mdl_upgrade(thd->open_tables, t->db, - t->table_name, FALSE)) + if (!find_table_for_mdl_upgrade(thd, t->db, t->table_name, false)) return 1; } else { + /* + It is not safe to upgrade the metadata lock without GLOBAL IX lock. + This can happen with FLUSH TABLES WITH READ LOCK as we in these + cases don't take a GLOBAL IX lock in order to be compatible with + global read lock. + */ + if (thd->open_tables && + !thd->mdl_context.is_lock_owner(MDL_key::GLOBAL, "", "", + MDL_INTENTION_EXCLUSIVE)) + { + my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), + thd->open_tables->s->table_name.str); + return true; + } + for (TABLE *tab= thd->open_tables; tab; tab= tab->next) { if (! tab->mdl_ticket->is_upgradable_or_exclusive()) -- cgit v1.2.1