diff options
| -rw-r--r-- | mysql-test/r/mysqld--help-notwin.result | 3 | ||||
| -rw-r--r-- | mysql-test/r/mysqld--help-win.result | 3 | ||||
| -rw-r--r-- | mysql-test/suite/sys_vars/r/metadata_locks_cache_size_basic.result | 21 | ||||
| -rw-r--r-- | mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic-master.opt | 1 | ||||
| -rw-r--r-- | mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic.test | 25 | ||||
| -rw-r--r-- | sql/mdl.cc | 266 | ||||
| -rw-r--r-- | sql/mdl.h | 8 | ||||
| -rw-r--r-- | sql/sql_plist.h | 9 | ||||
| -rw-r--r-- | sql/sys_vars.cc | 6 |
9 files changed, 297 insertions, 45 deletions
diff --git a/mysql-test/r/mysqld--help-notwin.result b/mysql-test/r/mysqld--help-notwin.result index b4faa833c1b..cb727984ec0 100644 --- a/mysql-test/r/mysqld--help-notwin.result +++ b/mysql-test/r/mysqld--help-notwin.result @@ -336,6 +336,8 @@ The following options may be given as the first argument: After this many write locks, allow some read locks to run in between --memlock Lock mysqld in memory. + --metadata-locks-cache-size=# + Size of unused metadata locks cache --min-examined-row-limit=# Don't write queries to slow log that examine fewer rows than that @@ -844,6 +846,7 @@ max-tmp-tables 32 max-user-connections 0 max-write-lock-count 18446744073709551615 memlock FALSE +metadata-locks-cache-size 1024 min-examined-row-limit 0 multi-range-count 256 myisam-block-size 1024 diff --git a/mysql-test/r/mysqld--help-win.result b/mysql-test/r/mysqld--help-win.result index 361d30620f7..38235e1a093 100644 --- a/mysql-test/r/mysqld--help-win.result +++ b/mysql-test/r/mysqld--help-win.result @@ -335,6 +335,8 @@ The following options may be given as the first argument: After this many write locks, allow some read locks to run in between --memlock Lock mysqld in memory. + --metadata-locks-cache-size=# + Size of unused metadata locks cache --min-examined-row-limit=# Don't write queries to slow log that examine fewer rows than that @@ -847,6 +849,7 @@ max-tmp-tables 32 max-user-connections 0 max-write-lock-count 18446744073709551615 memlock FALSE +metadata-locks-cache-size 1024 min-examined-row-limit 0 multi-range-count 256 myisam-block-size 1024 diff --git a/mysql-test/suite/sys_vars/r/metadata_locks_cache_size_basic.result b/mysql-test/suite/sys_vars/r/metadata_locks_cache_size_basic.result new file mode 100644 index 00000000000..a62b6011739 --- /dev/null +++ b/mysql-test/suite/sys_vars/r/metadata_locks_cache_size_basic.result @@ -0,0 +1,21 @@ +# +# Check that the paremeter is correctly set by start-up +# option (.opt file sets it to 256 while default is 1024). +select @@global.metadata_locks_cache_size = 256; +@@global.metadata_locks_cache_size = 256 +1 +# +# Check that variable is read only +# +set @@global.metadata_locks_cache_size= 1024; +ERROR HY000: Variable 'metadata_locks_cache_size' is a read only variable +select @@global.metadata_locks_cache_size = 256; +@@global.metadata_locks_cache_size = 256 +1 +# +# And only GLOBAL +# +select @@session.metadata_locks_cache_size; +ERROR HY000: Variable 'metadata_locks_cache_size' is a GLOBAL variable +set @@session.metadata_locks_cache_size= 1024; +ERROR HY000: Variable 'metadata_locks_cache_size' is a read only variable diff --git a/mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic-master.opt b/mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic-master.opt new file mode 100644 index 00000000000..77e019cd3d4 --- /dev/null +++ b/mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic-master.opt @@ -0,0 +1 @@ +--metadata-locks-cache-size=256 diff --git a/mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic.test b/mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic.test new file mode 100644 index 00000000000..31b033579c6 --- /dev/null +++ b/mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic.test @@ -0,0 +1,25 @@ +# +# Basic test coverage for --metadata-locks-cache-size startup +# parameter and corresponding read-only global @@metadata_locks_cache_size +# variable. +# + +--echo # +--echo # Check that the paremeter is correctly set by start-up +--echo # option (.opt file sets it to 256 while default is 1024). +select @@global.metadata_locks_cache_size = 256; + +--echo # +--echo # Check that variable is read only +--echo # +--error ER_INCORRECT_GLOBAL_LOCAL_VAR +set @@global.metadata_locks_cache_size= 1024; +select @@global.metadata_locks_cache_size = 256; + +--echo # +--echo # And only GLOBAL +--echo # +--error ER_INCORRECT_GLOBAL_LOCAL_VAR +select @@session.metadata_locks_cache_size; +--error ER_INCORRECT_GLOBAL_LOCAL_VAR +set @@session.metadata_locks_cache_size= 1024; diff --git a/sql/mdl.cc b/sql/mdl.cc index 046ac25703a..81d6c69dca4 100644 --- a/sql/mdl.cc +++ b/sql/mdl.cc @@ -91,6 +91,10 @@ const char *MDL_key::m_namespace_to_wait_state_name[NAMESPACE_END]= static bool mdl_initialized= 0; +class MDL_object_lock; +class MDL_object_lock_cache_adapter; + + /** A collection of all MDL locks. A singleton, there is only one instance of the map in the server. @@ -111,6 +115,25 @@ private: HASH m_locks; /* Protects access to m_locks hash. */ mysql_mutex_t m_mutex; + /** + Cache of (unused) MDL_lock objects available for re-use. + + On some systems (e.g. Windows XP) constructing/destructing + MDL_lock objects can be fairly expensive. We use this cache + to avoid these costs in scenarios in which they can have + significant negative effect on performance. For example, when + there is only one thread constantly executing statements in + auto-commit mode and thus constantly causing creation/ + destruction of MDL_lock objects for the tables it uses. + + Note that this cache contains only MDL_object_lock objects. + + Protected by m_mutex mutex. + */ + typedef I_P_List<MDL_object_lock, MDL_object_lock_cache_adapter, + I_P_List_counter> + Lock_cache; + Lock_cache m_unused_locks_cache; /** Pre-allocated MDL_lock object for GLOBAL namespace. */ MDL_lock *m_global_lock; /** Pre-allocated MDL_lock object for COMMIT namespace. */ @@ -379,7 +402,8 @@ public: : key(key_arg), m_ref_usage(0), m_ref_release(0), - m_is_destroyed(FALSE) + m_is_destroyed(FALSE), + m_version(0) { mysql_prlock_init(key_MDL_lock_rwlock, &m_rwlock); } @@ -414,6 +438,22 @@ public: uint m_ref_usage; uint m_ref_release; bool m_is_destroyed; + /** + We use the same idea and an additional version counter to support + caching of unused MDL_lock object for further re-use. + This counter is incremented while holding both MDL_map::m_mutex and + MDL_lock::m_rwlock locks each time when a MDL_lock is moved from + the hash to the unused objects list (or destroyed). + A thread, which has found a MDL_lock object for the key in the hash + and then released the MDL_map::m_mutex before acquiring the + MDL_lock::m_rwlock, can determine that this object was moved to the + unused objects list (or destroyed) while it held no locks by comparing + the version value which it read while holding the MDL_map::m_mutex + with the value read after acquiring the MDL_lock::m_rwlock. + Note that since it takes several years to overflow this counter such + theoretically possible overflows should not have any practical effects. + */ + ulonglong m_version; }; @@ -462,6 +502,26 @@ public: : MDL_lock(key_arg) { } + /** + Reset unused MDL_object_lock object to represent the lock context for a + different object. + */ + void reset(const MDL_key *new_key) + { + /* We need to change only object's key. */ + key.mdl_key_init(new_key); + /* m_granted and m_waiting should be already in the empty/initial state. */ + DBUG_ASSERT(is_empty()); + /* Object should not be marked as destroyed. */ + DBUG_ASSERT(! m_is_destroyed); + /* + Values of the rest of the fields should be preserved between old and + new versions of the object. E.g., m_version and m_ref_usage/release + should be kept intact to properly handle possible remaining references + to the old version of the object. + */ + } + virtual const bitmap_t *incompatible_granted_types_bitmap() const { return m_granted_incompatible; @@ -479,10 +539,29 @@ public: private: static const bitmap_t m_granted_incompatible[MDL_TYPE_END]; static const bitmap_t m_waiting_incompatible[MDL_TYPE_END]; + +public: + /** Members for linking the object into the list of unused objects. */ + MDL_object_lock *next_in_cache, **prev_in_cache; +}; + + +/** + Helper class for linking MDL_object_lock objects into the unused objects list. +*/ +class MDL_object_lock_cache_adapter : + public I_P_List_adapter<MDL_object_lock, &MDL_object_lock::next_in_cache, + &MDL_object_lock::prev_in_cache> +{ }; static MDL_map mdl_locks; +/** + Start-up parameter for the maximum size of the unused MDL_lock objects cache. +*/ +ulong mdl_locks_cache_size; + extern "C" { @@ -565,6 +644,10 @@ void MDL_map::destroy() my_hash_free(&m_locks); MDL_lock::destroy(m_global_lock); MDL_lock::destroy(m_commit_lock); + + MDL_object_lock *lock; + while ((lock= m_unused_locks_cache.pop_front())) + MDL_lock::destroy(lock); } @@ -614,11 +697,49 @@ retry: mdl_key->ptr(), mdl_key->length()))) { - lock= MDL_lock::create(mdl_key); + MDL_object_lock *unused_lock= NULL; + + /* + No lock object found so we need to create a new one + or reuse an existing unused object. + */ + if (mdl_key->mdl_namespace() != MDL_key::SCHEMA && + m_unused_locks_cache.elements()) + { + /* + We need a MDL_object_lock type of object and the unused objects + cache has some. Get the first object from the cache and set a new + key for it. + */ + DBUG_ASSERT(mdl_key->mdl_namespace() != MDL_key::GLOBAL && + mdl_key->mdl_namespace() != MDL_key::COMMIT); + + unused_lock= m_unused_locks_cache.pop_front(); + unused_lock->reset(mdl_key); + + lock= unused_lock; + } + else + { + lock= MDL_lock::create(mdl_key); + } + if (!lock || my_hash_insert(&m_locks, (uchar*)lock)) { + if (unused_lock) + { + /* + Note that we can't easily destroy an object from cache here as it + still might be referenced by other threads. So we simply put it + back into the cache. + */ + m_unused_locks_cache.push_front(unused_lock); + } + else + { + MDL_lock::destroy(lock); + } mysql_mutex_unlock(&m_mutex); - MDL_lock::destroy(lock); return NULL; } } @@ -633,7 +754,7 @@ retry: /** Release mdl_locks.m_mutex mutex and lock MDL_lock::m_rwlock for lock object from the hash. Handle situation when object was released - while the held no mutex. + while we held no locks. @retval FALSE - Success. @retval TRUE - Object was released while we held no mutex, caller @@ -642,6 +763,8 @@ retry: bool MDL_map::move_from_hash_to_lock_mutex(MDL_lock *lock) { + ulonglong version; + DBUG_ASSERT(! lock->m_is_destroyed); mysql_mutex_assert_owner(&m_mutex); @@ -651,26 +774,50 @@ bool MDL_map::move_from_hash_to_lock_mutex(MDL_lock *lock) m_is_destroyed is FALSE. */ lock->m_ref_usage++; + /* Read value of the version counter under protection of m_mutex lock. */ + version= lock->m_version; mysql_mutex_unlock(&m_mutex); mysql_prlock_wrlock(&lock->m_rwlock); lock->m_ref_release++; - if (unlikely(lock->m_is_destroyed)) + + if (unlikely(lock->m_version != version)) { /* - Object was released while we held no mutex, we need to - release it if no others hold references to it, while our own - reference count ensured that the object as such haven't got - its memory released yet. We can also safely compare - m_ref_usage and m_ref_release since the object is no longer - present in the hash so no one will be able to find it and - increment m_ref_usage anymore. + If the current value of version differs from one that was read while + we held m_mutex mutex, this MDL_lock object was moved to the unused + objects list or destroyed while we held no locks. + We should retry our search. But first we should destroy the MDL_lock + object if necessary. */ - uint ref_usage= lock->m_ref_usage; - uint ref_release= lock->m_ref_release; - mysql_prlock_unlock(&lock->m_rwlock); - if (ref_usage == ref_release) - MDL_lock::destroy(lock); + if (unlikely(lock->m_is_destroyed)) + { + /* + Object was released while we held no locks, we need to + release it if no others hold references to it, while our own + reference count ensured that the object as such haven't got + its memory released yet. We can also safely compare + m_ref_usage and m_ref_release since the object is no longer + present in the hash (or unused objects list) so no one will + be able to find it and increment m_ref_usage anymore. + */ + uint ref_usage= lock->m_ref_usage; + uint ref_release= lock->m_ref_release; + mysql_prlock_unlock(&lock->m_rwlock); + if (ref_usage == ref_release) + MDL_lock::destroy(lock); + } + else + { + /* + Object was not destroyed but its version has changed. + This means that it was moved to the unused objects list + (and even might be already re-used). So now it might + correspond to a different key, therefore we should simply + retry our search. + */ + mysql_prlock_unlock(&lock->m_rwlock); + } return TRUE; } return FALSE; @@ -685,8 +832,6 @@ bool MDL_map::move_from_hash_to_lock_mutex(MDL_lock *lock) void MDL_map::remove(MDL_lock *lock) { - uint ref_usage, ref_release; - if (lock->key.mdl_namespace() == MDL_key::GLOBAL || lock->key.mdl_namespace() == MDL_key::COMMIT) { @@ -698,31 +843,65 @@ void MDL_map::remove(MDL_lock *lock) return; } - /* - Destroy the MDL_lock object, but ensure that anyone that is - holding a reference to the object is not remaining, if so he - has the responsibility to release it. - - Setting of m_is_destroyed to TRUE while holding _both_ - mdl_locks.m_mutex and MDL_lock::m_rwlock mutexes transfers the - protection of m_ref_usage from mdl_locks.m_mutex to - MDL_lock::m_rwlock while removal of object from the hash makes - it read-only. Therefore whoever acquires MDL_lock::m_rwlock next - will see most up to date version of m_ref_usage. - - This means that when m_is_destroyed is TRUE and we hold the - MDL_lock::m_rwlock we can safely read the m_ref_usage - member. - */ mysql_mutex_lock(&m_mutex); my_hash_delete(&m_locks, (uchar*) lock); - lock->m_is_destroyed= TRUE; - ref_usage= lock->m_ref_usage; - ref_release= lock->m_ref_release; - mysql_prlock_unlock(&lock->m_rwlock); - mysql_mutex_unlock(&m_mutex); - if (ref_usage == ref_release) - MDL_lock::destroy(lock); + /* + To let threads holding references to the MDL_lock object know that it was + moved to the list of unused objects or destroyed, we increment the version + counter under protection of both MDL_map::m_mutex and MDL_lock::m_rwlock + locks. This allows us to read the version value while having either one + of those locks. + */ + lock->m_version++; + + if ((lock->key.mdl_namespace() != MDL_key::SCHEMA) && + (m_unused_locks_cache.elements() < mdl_locks_cache_size)) + { + /* + This is an object of MDL_object_lock type and the cache of unused + objects has not reached its maximum size yet. So instead of destroying + object we move it to the list of unused objects to allow its later + re-use with possibly different key. Any threads holding references to + this object (owning MDL_map::m_mutex or MDL_lock::m_rwlock) will notice + this thanks to the fact that we have changed the MDL_lock::m_version + counter. + */ + DBUG_ASSERT(lock->key.mdl_namespace() != MDL_key::GLOBAL && + lock->key.mdl_namespace() != MDL_key::COMMIT); + + m_unused_locks_cache.push_front((MDL_object_lock*)lock); + mysql_mutex_unlock(&m_mutex); + mysql_prlock_unlock(&lock->m_rwlock); + } + else + { + /* + Destroy the MDL_lock object, but ensure that anyone that is + holding a reference to the object is not remaining, if so he + has the responsibility to release it. + + Setting of m_is_destroyed to TRUE while holding _both_ + mdl_locks.m_mutex and MDL_lock::m_rwlock mutexes transfers the + protection of m_ref_usage from mdl_locks.m_mutex to + MDL_lock::m_rwlock while removal of the object from the hash + (and cache of unused objects) makes it read-only. Therefore + whoever acquires MDL_lock::m_rwlock next will see the most up + to date version of m_ref_usage. + + This means that when m_is_destroyed is TRUE and we hold the + MDL_lock::m_rwlock we can safely read the m_ref_usage + member. + */ + uint ref_usage, ref_release; + + lock->m_is_destroyed= TRUE; + ref_usage= lock->m_ref_usage; + ref_release= lock->m_ref_release; + mysql_mutex_unlock(&m_mutex); + mysql_prlock_unlock(&lock->m_rwlock); + if (ref_usage == ref_release) + MDL_lock::destroy(lock); + } } @@ -820,9 +999,6 @@ void MDL_request::init(const MDL_key *key_arg, Auxiliary functions needed for creation/destruction of MDL_lock objects. @note Also chooses an MDL_lock descendant appropriate for object namespace. - - @todo This naive implementation should be replaced with one that saves - on memory allocation by reusing released objects. */ inline MDL_lock *MDL_lock::create(const MDL_key *mdl_key) diff --git a/sql/mdl.h b/sql/mdl.h index fb2de45b831..5c1af23f5e2 100644 --- a/sql/mdl.h +++ b/sql/mdl.h @@ -851,4 +851,12 @@ extern "C" void thd_exit_cond(MYSQL_THD thd, const char *old_msg); extern mysql_mutex_t LOCK_open; #endif + +/* + Start-up parameter for the maximum size of the unused MDL_lock objects cache + and a constant for its default value. +*/ +extern ulong mdl_locks_cache_size; +static const ulong MDL_LOCKS_CACHE_SIZE_DEFAULT = 1024; + #endif diff --git a/sql/sql_plist.h b/sql/sql_plist.h index ca1d15f3015..2b6f1067321 100644 --- a/sql/sql_plist.h +++ b/sql/sql_plist.h @@ -128,6 +128,15 @@ public: } inline T* front() { return m_first; } inline const T *front() const { return m_first; } + inline T* pop_front() + { + T *result= front(); + + if (result) + remove(result); + + return result; + } void swap(I_P_List<T, B, C> &rhs) { swap_variables(T *, m_first, rhs.m_first); diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc index da8e61da52e..7a04015dc93 100644 --- a/sql/sys_vars.cc +++ b/sql/sys_vars.cc @@ -1156,6 +1156,12 @@ static Sys_var_ulonglong Sys_max_heap_table_size( VALID_RANGE(16384, (ulonglong)~(intptr)0), DEFAULT(16*1024*1024), BLOCK_SIZE(1024)); +static Sys_var_ulong Sys_metadata_locks_cache_size( + "metadata_locks_cache_size", "Size of unused metadata locks cache", + READ_ONLY GLOBAL_VAR(mdl_locks_cache_size), CMD_LINE(REQUIRED_ARG), + VALID_RANGE(1, 1024*1024), DEFAULT(MDL_LOCKS_CACHE_SIZE_DEFAULT), + BLOCK_SIZE(1)); + static Sys_var_ulong Sys_pseudo_thread_id( "pseudo_thread_id", "This variable is for internal server use", |