diff options
| -rw-r--r-- | mysql-test/r/information_schema.result | 114 | ||||
| -rw-r--r-- | mysql-test/t/information_schema.test | 182 | ||||
| -rw-r--r-- | sql/sql_show.cc | 33 |
3 files changed, 322 insertions, 7 deletions
diff --git a/mysql-test/r/information_schema.result b/mysql-test/r/information_schema.result index 1418af5b813..88a56edbb5c 100644 --- a/mysql-test/r/information_schema.result +++ b/mysql-test/r/information_schema.result @@ -1849,5 +1849,119 @@ unlock tables; drop table t1; drop view v1; # +# Test for bug #12828477 - "MDL SUBSYSTEM CREATES BIG OVERHEAD FOR +# CERTAIN QUERIES TO INFORMATION_SCHEMA". +# +# Check that metadata locks which are acquired during the process +# of opening tables/.FRMs/.TRG files while filling I_S table are +# not kept to the end of statement. Keeping the locks has caused +# performance problems in cases when big number of tables (.FRMs +# or .TRG files) were scanned as cost of new lock acquisition has +# increased linearly. +drop database if exists mysqltest; +create database mysqltest; +use mysqltest; +create table t0 (i int); +create table t1 (j int); +create table t2 (k int); +# +# Test that we don't keep locks in case when we to fill +# I_S table we perform full-blown table open. +# +# Acquire lock on 't2' so upcoming RENAME is +# blocked. +lock tables t2 read; +# +# Switching to connection 'con12828477_1'. +# +# The below RENAME should wait on 't2' while +# keeping X lock on 't1'. +rename table t1 to t3, t2 to t1, t3 to t2; +# +# Switching to connection 'con12828477_2'. +# +# Wait while the above RENAME is blocked. +# Issue query to I_S which will open 't0' and get +# blocked on 't1' because of RENAME. +select table_name, auto_increment from information_schema.tables where table_schema='mysqltest'; +# +# Switching to connection 'con12828477_3'. +# +# Wait while the above SELECT is blocked. +# +# Check that it holds no lock on 't0' so it can be renamed. +rename table t0 to t4; +# +# Switching to connection 'default'. +# +# +# Unblock the first RENAME. +unlock tables; +# +# Switching to connection 'con12828477_1'. +# +# Reap the first RENAME +# +# Switching to connection 'con12828477_2'. +# +# Reap SELECT to I_S. +table_name auto_increment +t0 NULL +t1 NULL +t2 NULL +# +# Switching to connection 'default'. +# +# +# Now test that we don't keep locks in case when we to fill +# I_S table we read .FRM or .TRG file only (this was the case +# for which problem existed). +# +rename table t4 to t0; +# Acquire lock on 't2' so upcoming RENAME is +# blocked. +lock tables t2 read; +# +# Switching to connection 'con12828477_1'. +# +# The below RENAME should wait on 't2' while +# keeping X lock on 't1'. +rename table t1 to t3, t2 to t1, t3 to t2; +# +# Switching to connection 'con12828477_2'. +# +# Wait while the above RENAME is blocked. +# Issue query to I_S which will open 't0' and get +# blocked on 't1' because of RENAME. +select event_object_table, trigger_name from information_schema.triggers where event_object_schema='mysqltest'; +# +# Switching to connection 'con12828477_3'. +# +# Wait while the above SELECT is blocked. +# +# Check that it holds no lock on 't0' so it can be renamed. +rename table t0 to t4; +# +# Switching to connection 'default'. +# +# +# Unblock the first RENAME. +unlock tables; +# +# Switching to connection 'con12828477_1'. +# +# Reap the first RENAME +# +# Switching to connection 'con12828477_2'. +# +# Reap SELECT to I_S. +event_object_table trigger_name +# +# Switching to connection 'default'. +# +# +# Clean-up. +drop database mysqltest; +# # End of 5.5 tests # diff --git a/mysql-test/t/information_schema.test b/mysql-test/t/information_schema.test index 589bb898d6a..e6dc989bdb9 100644 --- a/mysql-test/t/information_schema.test +++ b/mysql-test/t/information_schema.test @@ -1543,8 +1543,6 @@ DROP TABLE t1, information_schema.tables; LOCK TABLES t1 READ, information_schema.tables READ; DROP TABLE t1; -# Wait till all disconnects are completed ---source include/wait_until_count_sessions.inc # # Bug #43834 Assertion in Natural_join_column::db_name() on an I_S query @@ -1609,5 +1607,185 @@ drop view v1; --echo # +--echo # Test for bug #12828477 - "MDL SUBSYSTEM CREATES BIG OVERHEAD FOR +--echo # CERTAIN QUERIES TO INFORMATION_SCHEMA". +--echo # +--echo # Check that metadata locks which are acquired during the process +--echo # of opening tables/.FRMs/.TRG files while filling I_S table are +--echo # not kept to the end of statement. Keeping the locks has caused +--echo # performance problems in cases when big number of tables (.FRMs +--echo # or .TRG files) were scanned as cost of new lock acquisition has +--echo # increased linearly. +--disable_warnings +drop database if exists mysqltest; +--enable_warnings +create database mysqltest; +use mysqltest; +create table t0 (i int); +create table t1 (j int); +create table t2 (k int); + +--echo # +--echo # Test that we don't keep locks in case when we to fill +--echo # I_S table we perform full-blown table open. +--echo # + +--echo # Acquire lock on 't2' so upcoming RENAME is +--echo # blocked. +lock tables t2 read; + +--echo # +--echo # Switching to connection 'con12828477_1'. +--echo # +connect (con12828477_1, localhost, root,,mysqltest); +--echo # The below RENAME should wait on 't2' while +--echo # keeping X lock on 't1'. +--send rename table t1 to t3, t2 to t1, t3 to t2 + +--echo # +--echo # Switching to connection 'con12828477_2'. +--echo # +connect (con12828477_2, localhost, root,,mysqltest); +--echo # Wait while the above RENAME is blocked. +let $wait_condition= + select count(*) = 1 from information_schema.processlist + where state = "Waiting for table metadata lock" and + info = "rename table t1 to t3, t2 to t1, t3 to t2"; +--source include/wait_condition.inc + +--echo # Issue query to I_S which will open 't0' and get +--echo # blocked on 't1' because of RENAME. +--send select table_name, auto_increment from information_schema.tables where table_schema='mysqltest' + +--echo # +--echo # Switching to connection 'con12828477_3'. +--echo # +connect (con12828477_3, localhost, root,,mysqltest); +--echo # Wait while the above SELECT is blocked. +let $wait_condition= + select count(*) = 1 from information_schema.processlist + where state = "Waiting for table metadata lock" and + info = "select table_name, auto_increment from information_schema.tables where table_schema='mysqltest'"; +--source include/wait_condition.inc + +--echo # +--echo # Check that it holds no lock on 't0' so it can be renamed. +rename table t0 to t4; + +--echo # +--echo # Switching to connection 'default'. +--echo # +connection default; +--echo # +--echo # Unblock the first RENAME. +unlock tables; + +--echo # +--echo # Switching to connection 'con12828477_1'. +--echo # +connection con12828477_1; +--echo # Reap the first RENAME +--reap + +--echo # +--echo # Switching to connection 'con12828477_2'. +--echo # +connection con12828477_2; +--echo # Reap SELECT to I_S. +--reap + +--echo # +--echo # Switching to connection 'default'. +--echo # +connection default; + +--echo # +--echo # Now test that we don't keep locks in case when we to fill +--echo # I_S table we read .FRM or .TRG file only (this was the case +--echo # for which problem existed). +--echo # + +rename table t4 to t0; +--echo # Acquire lock on 't2' so upcoming RENAME is +--echo # blocked. +lock tables t2 read; + +--echo # +--echo # Switching to connection 'con12828477_1'. +--echo # +connection con12828477_1; +--echo # The below RENAME should wait on 't2' while +--echo # keeping X lock on 't1'. +--send rename table t1 to t3, t2 to t1, t3 to t2 + +--echo # +--echo # Switching to connection 'con12828477_2'. +--echo # +connection con12828477_2; +--echo # Wait while the above RENAME is blocked. +let $wait_condition= + select count(*) = 1 from information_schema.processlist + where state = "Waiting for table metadata lock" and + info = "rename table t1 to t3, t2 to t1, t3 to t2"; +--source include/wait_condition.inc + +--echo # Issue query to I_S which will open 't0' and get +--echo # blocked on 't1' because of RENAME. +--send select event_object_table, trigger_name from information_schema.triggers where event_object_schema='mysqltest' + +--echo # +--echo # Switching to connection 'con12828477_3'. +--echo # +connection con12828477_3; +--echo # Wait while the above SELECT is blocked. +let $wait_condition= + select count(*) = 1 from information_schema.processlist + where state = "Waiting for table metadata lock" and + info = "select event_object_table, trigger_name from information_schema.triggers where event_object_schema='mysqltest'"; +--source include/wait_condition.inc + +--echo # +--echo # Check that it holds no lock on 't0' so it can be renamed. +rename table t0 to t4; + +--echo # +--echo # Switching to connection 'default'. +--echo # +connection default; +--echo # +--echo # Unblock the first RENAME. +unlock tables; + +--echo # +--echo # Switching to connection 'con12828477_1'. +--echo # +connection con12828477_1; +--echo # Reap the first RENAME +--reap + +--echo # +--echo # Switching to connection 'con12828477_2'. +--echo # +connection con12828477_2; +--echo # Reap SELECT to I_S. +--reap + +--echo # +--echo # Switching to connection 'default'. +--echo # +connection default; +disconnect con12828477_1; +disconnect con12828477_2; +disconnect con12828477_3; + +--echo # +--echo # Clean-up. +drop database mysqltest; + + +--echo # --echo # End of 5.5 tests --echo # + +# Wait till all disconnects are completed +--source include/wait_until_count_sessions.inc diff --git a/sql/sql_show.cc b/sql/sql_show.cc index fb5ed62ecdf..887115b38ad 100644 --- a/sql/sql_show.cc +++ b/sql/sql_show.cc @@ -3157,6 +3157,10 @@ end: */ thd->temporary_tables= NULL; close_thread_tables(thd); + /* + Release metadata lock we might have acquired. + See comment in fill_schema_table_from_frm() for details. + */ thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp); thd->lex= old_lex; @@ -3339,6 +3343,9 @@ try_acquire_high_prio_shared_mdl_lock(THD *thd, TABLE_LIST *table, @param[in] db_name database name @param[in] table_name table name @param[in] schema_table_idx I_S table index + @param[in] open_tables_state_backup Open_tables_state object which is used + to save/restore original state of metadata + locks. @param[in] can_deadlock Indicates that deadlocks are possible due to metadata locks, so to avoid them we should not wait in case if @@ -3356,6 +3363,7 @@ static int fill_schema_table_from_frm(THD *thd, TABLE_LIST *tables, LEX_STRING *db_name, LEX_STRING *table_name, enum enum_schema_tables schema_table_idx, + Open_tables_backup *open_tables_state_backup, bool can_deadlock) { TABLE *table= tables->table; @@ -3501,13 +3509,27 @@ end_share: end_unlock: mysql_mutex_unlock(&LOCK_open); - /* - Don't release the MDL lock, it can be part of a transaction. - If it is not, it will be released by the call to - MDL_context::rollback_to_savepoint() in the caller. - */ end: + /* + Release metadata lock we might have acquired. + + Without this step metadata locks acquired for each table processed + will be accumulated. In situation when a lot of tables are processed + by I_S query this will result in transaction with too many metadata + locks. As result performance of acquisition of new lock will suffer. + + Of course, the fact that we don't hold metadata lock on tables which + were processed till the end of I_S query makes execution less isolated + from concurrent DDL. Consequently one might get 'dirty' results from + such a query. But we have never promised serializability of I_S queries + anyway. + + We don't have any tables open since we took backup, so rolling back to + savepoint is safe. + */ + DBUG_ASSERT(thd->open_tables == NULL); + thd->mdl_context.rollback_to_savepoint(open_tables_state_backup->mdl_system_tables_svp); thd->clear_error(); return res; } @@ -3758,6 +3780,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond) int res= fill_schema_table_from_frm(thd, tables, schema_table, db_name, table_name, schema_table_idx, + &open_tables_state_backup, can_deadlock); thd->pop_internal_handler(); |