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Message #08052
Re: [Commits] b2f45ba: MDEV-7324 - Lock-free hash for table definition cache
Hi, Sergey!
On Dec 22, svoj@xxxxxxxxxxx wrote:
> revision-id: b2f45ba8280c97f8dc8b1adb3234cf2e28e48982
> parent(s): 4a469b0ed68bb341e1a1e1ba540a45a3b6ff3ef9
> committer: Sergey Vojtovich
> branch nick: 10.1
> timestamp: 2014-12-22 19:56:48 +0400
> message:
>
> MDEV-7324 - Lock-free hash for table definition cache
That looked good to me.
I didn't find anything obviously wrong.
There are mostly questions below.
Some are style suggestions (like, renaming of methods, etc).
The only place I'm not sure about is early lf_hash_search_unpin()
in tdc_acquire_share().
> diff --git a/mysys/lf_hash.c b/mysys/lf_hash.c
> --- a/mysys/lf_hash.c
> +++ b/mysys/lf_hash.c
> @@ -122,7 +122,7 @@ static int lfind(LF_SLIST * volatile *head, CHARSET_INFO *cs, uint32 hashnr,
> {
> if (unlikely(callback))
> {
> - if (callback(cursor->curr + 1, (void*)key))
> + if (cur_hashnr & 1 && callback(cursor->curr + 1, (void*)key))
Sorry for this.
> return 1;
> }
> else if (cur_hashnr >= hashnr)
> diff --git a/sql/sql_class.cc b/sql/sql_class.cc
> --- a/sql/sql_class.cc
> +++ b/sql/sql_class.cc
> @@ -912,17 +912,17 @@ bool Drop_table_error_handler::handle_condition(THD *thd,
> #endif /* defined(ENABLED_DEBUG_SYNC) */
> wait_for_commit_ptr(0),
> main_da(0, false, false),
> - m_stmt_da(&main_da)
> + m_stmt_da(&main_da),
> #ifdef WITH_WSREP
> - ,
> wsrep_applier(is_wsrep_applier),
> wsrep_applier_closing(false),
> wsrep_client_thread(false),
> wsrep_apply_toi(false),
> wsrep_po_handle(WSREP_PO_INITIALIZER),
> wsrep_po_cnt(0),
> - wsrep_apply_format(0)
> + wsrep_apply_format(0),
> #endif
> + tdc_hash_pins(0)
Eh... I actually wanted wsrep related data to the at the end of the THD.
Just to keep the rest of the THD layout identical for wsrep and non-wsrep
builds. In case a wsrep-enabled plugin is loaded into non-wsrep server or
visa versa. That was an early change, though, I've done more cleanups after
that and moved wsrep into a service, so perhaps (even, most probably)
this is not needed anymore. But I'd better stay on the safe side and keep
wsrep at the end of THD.
> {
> ulong tmp;
>
> @@ -1698,6 +1698,8 @@ void THD::cleanup(void)
>
> free_root(&main_mem_root, MYF(0));
> main_da.free_memory();
> + if (tdc_hash_pins)
> + lf_hash_put_pins(tdc_hash_pins);
no tdc_hash_pins=0 here?
> if (status_var.memory_used != 0)
> {
> DBUG_PRINT("error", ("memory_used: %lld", status_var.memory_used));
> diff --git a/sql/table.h b/sql/table.h
> --- a/sql/table.h
> +++ b/sql/table.h
> @@ -611,32 +612,7 @@ struct TABLE_SHARE
> mysql_mutex_t LOCK_ha_data; /* To protect access to ha_data */
> mysql_mutex_t LOCK_share; /* To protect TABLE_SHARE */
>
> - typedef I_P_List <TABLE, TABLE_share> TABLE_list;
> - typedef I_P_List <TABLE, All_share_tables> All_share_tables_list;
> - struct
> - {
> - /**
> - Protects ref_count, m_flush_tickets, all_tables, free_tables, flushed,
> - all_tables_refs.
> - */
> - mysql_mutex_t LOCK_table_share;
> - mysql_cond_t COND_release;
> - TABLE_SHARE *next, **prev; /* Link to unused shares */
> - uint ref_count; /* How many TABLE objects uses this */
> - uint all_tables_refs; /* Number of refs to all_tables */
> - /**
> - List of tickets representing threads waiting for the share to be flushed.
> - */
> - Wait_for_flush_list m_flush_tickets;
> - /*
> - Doubly-linked (back-linked) lists of used and unused TABLE objects
> - for this share.
> - */
> - All_share_tables_list all_tables;
> - TABLE_list free_tables;
> - ulong version;
> - bool flushed;
> - } tdc;
> + TDC_element *tdc;
Hmm. Ok. I think I like this change - TABLE_SHARE now contains table metadata
and everything related to tdc is moved to TDC_element. Right?
>
> LEX_CUSTRING tabledef_version;
>
> diff --git a/sql/table.cc b/sql/table.cc
> --- a/sql/table.cc
> +++ b/sql/table.cc
> @@ -3845,11 +3844,11 @@ bool TABLE_SHARE::visit_subgraph(Wait_for_flush *wait_for_flush,
> because we won't try to acquire tdc.LOCK_table_share while
> holding a write-lock on MDL_lock::m_rwlock.
> */
> - mysql_mutex_lock(&tdc.LOCK_table_share);
> - tdc.all_tables_refs++;
> - mysql_mutex_unlock(&tdc.LOCK_table_share);
> + mysql_mutex_lock(&tdc->LOCK_table_share);
> + tdc->all_tables_refs++;
> + mysql_mutex_unlock(&tdc->LOCK_table_share);
Do I understand it correctly that a TDC_element can never be deleted from
LF_HASH as long as at least one TABLE_SHARE references it?
>
> - All_share_tables_list::Iterator tables_it(tdc.all_tables);
> + TDC_element::All_share_tables_list::Iterator tables_it(tdc->all_tables);
>
> /*
> In case of multiple searches running in parallel, avoid going
> @@ -3946,21 +3945,10 @@ bool TABLE_SHARE::wait_for_old_version(THD *thd, struct timespec *abstime,
>
> mdl_context->done_waiting_for();
>
> - mysql_mutex_lock(&tdc.LOCK_table_share);
> -
> - tdc.m_flush_tickets.remove(&ticket);
> -
> - if (tdc.m_flush_tickets.is_empty() && tdc.ref_count == 0)
> - {
> - /*
> - If our thread was the last one using the share,
> - we must destroy it here.
> - */
> - mysql_mutex_unlock(&tdc.LOCK_table_share);
> - destroy();
> - }
> - else
> - mysql_mutex_unlock(&tdc.LOCK_table_share);
> + mysql_mutex_lock(&tdc->LOCK_table_share);
> + tdc->m_flush_tickets.remove(&ticket);
> + mysql_cond_broadcast(&tdc->COND_release);
> + mysql_mutex_unlock(&tdc->LOCK_table_share);
Why is the logic here different?
>
>
> /*
> diff --git a/sql/table_cache.h b/sql/table_cache.h
> --- a/sql/table_cache.h
> +++ b/sql/table_cache.h
> @@ -16,6 +16,171 @@
> Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
>
>
> +extern PSI_mutex_key key_TABLE_SHARE_LOCK_table_share;
> +extern PSI_cond_key key_TABLE_SHARE_COND_release;
> +
> +class TDC_element
> +{
> +public:
> + uchar m_key[NAME_LEN + 1 + NAME_LEN + 1];
> + uint m_key_length;
> + ulong version;
> + bool flushed;
> + TABLE_SHARE *share;
> +
> + typedef I_P_List <TABLE, TABLE_share> TABLE_list;
> + typedef I_P_List <TABLE, All_share_tables> All_share_tables_list;
> + /**
> + Protects ref_count, m_flush_tickets, all_tables, free_tables, flushed,
> + all_tables_refs.
> + */
> + mysql_mutex_t LOCK_table_share;
> + mysql_cond_t COND_release;
> + TDC_element *next, **prev; /* Link to unused shares */
> + uint ref_count; /* How many TABLE objects uses this */
> + uint all_tables_refs; /* Number of refs to all_tables */
> + /**
> + List of tickets representing threads waiting for the share to be flushed.
> + */
> + Wait_for_flush_list m_flush_tickets;
> + /*
> + Doubly-linked (back-linked) lists of used and unused TABLE objects
> + for this share.
> + */
> + All_share_tables_list all_tables;
> + TABLE_list free_tables;
> +
> + TDC_element() {}
> +
> + TDC_element(const char *key, uint key_length) : m_key_length(key_length)
> + {
> + memcpy(m_key, key, key_length);
> + }
> +
> +
> + void dbug_release_assertions()
Somewhat confusing name. If I hadn't see the code below
I'd thought this function releases some assertions (how? why?)
may be assert_correctness_at_release() would be less ambiguous?
> + {
> + DBUG_ASSERT(share == 0);
> + DBUG_ASSERT(ref_count == 0);
> + DBUG_ASSERT(m_flush_tickets.is_empty());
> + DBUG_ASSERT(all_tables.is_empty());
> + DBUG_ASSERT(free_tables.is_empty());
> + DBUG_ASSERT(all_tables_refs == 0);
> + DBUG_ASSERT(next == 0);
> + DBUG_ASSERT(prev == 0);
> + }
> +
> +
> + /**
> + Acquire TABLE object from table cache.
> +
> + @pre share must be protected against removal.
> +
> + Acquired object cannot be evicted or acquired again.
> +
> + While locked:
> + - pop object from TABLE_SHARE::tdc.free_tables
> +
> + While unlocked:
> + - mark object used by thd
"While locked" / "While unlocked" - what does that mean?
> +
> + @return TABLE object, or NULL if no unused objects.
> + */
> +
> + TABLE *acquire_table(THD *thd)
> + {
> + TABLE *table;
> +
> + mysql_mutex_lock(&LOCK_table_share);
> + table= free_tables.pop_front();
> + if (table)
> + {
> + DBUG_ASSERT(!table->in_use);
lots of asserts - good!
> + table->in_use= thd;
> + /* The ex-unused table must be fully functional. */
> + DBUG_ASSERT(table->db_stat && table->file);
> + /* The children must be detached from the table. */
> + DBUG_ASSERT(!table->file->extra(HA_EXTRA_IS_ATTACHED_CHILDREN));
I don't even think of asking why it's HA_EXTRA_IS_ATTACHED_CHILDREN and not
HA_EXTRA_HAS_ATTACHED_CHILDREN or, at least, HA_EXTRA_CHILDREN_ARE_ATTACHED.
Ah, whatever... Horrors of the English language hidden in old MySQL code :)
> + }
> + mysql_mutex_unlock(&LOCK_table_share);
> + return table;
> + }
> +
> +
> + /**
> + Get last element of free_tables.
> + */
> +
> + TABLE *free_tables_back()
Eh, I've thought for a few seconds what could it mean to "free tables back"
until I read the function comment. You see, "free" is so often used as a verb
that one absolutely doesn't see it that here it means "free_tables' back"
even though it's also a common naming pattern (xxx_back for the list xxx).
Rename the method, may be?
> + {
> + TABLE_list::Iterator it(share->tdc->free_tables);
> + TABLE *entry, *last= 0;
> + while ((entry= it++))
> + last= entry;
> + return last;
> + }
> +
> +
> + /**
> + Wait for MDL deadlock detector to complete traversing tdc.all_tables.
> +
> + Must be called before updating TABLE_SHARE::tdc.all_tables.
> + */
> +
> + void wait_for_mdl_deadlock_detector()
> + {
> + while (all_tables_refs)
> + mysql_cond_wait(&COND_release, &LOCK_table_share);
> + }
> +
> +
> + /**
> + Prepeare table share for use with table definition cache.
> + */
> +
> + static void lf_alloc_constructor(uchar *arg)
> + {
> + TDC_element *element= (TDC_element*) (arg + LF_HASH_OVERHEAD);
> + DBUG_ENTER("tdc_init_share");
intentionally? or forgot to update DBUG_ENTER?
> + mysql_mutex_init(key_TABLE_SHARE_LOCK_table_share,
> + &element->LOCK_table_share, MY_MUTEX_INIT_FAST);
> + mysql_cond_init(key_TABLE_SHARE_COND_release, &element->COND_release, 0);
> + element->m_flush_tickets.empty();
> + element->all_tables.empty();
> + element->free_tables.empty();
> + element->all_tables_refs= 0;
> + element->share= 0;
> + element->ref_count= 0;
> + element->next= 0;
> + element->prev= 0;
> + DBUG_VOID_RETURN;
> + }
> +
> +
> + /**
> + Release table definition cache specific resources of table share.
> + */
> +
> + static void lf_alloc_destructor(uchar *arg)
> + {
> + TDC_element *element= (TDC_element*) (arg + LF_HASH_OVERHEAD);
> + DBUG_ENTER("tdc_deinit_share");
intentionally? or forgot to update DBUG_ENTER?
> + element->dbug_release_assertions();
> + mysql_cond_destroy(&element->COND_release);
> + mysql_mutex_destroy(&element->LOCK_table_share);
> + DBUG_VOID_RETURN;
> + }
> +
> +
> + static uchar *key(const TDC_element *element, size_t *length,
> + my_bool not_used __attribute__((unused)))
> + {
> + *length= element->m_key_length;
> + return (uchar*) element->m_key;
> + }
> +};
> +
> +
> enum enum_tdc_remove_table_type
> {
> TDC_RT_REMOVE_ALL,
> diff --git a/sql/sql_base.cc b/sql/sql_base.cc
> --- a/sql/sql_base.cc
> +++ b/sql/sql_base.cc
> @@ -270,58 +270,75 @@ uint get_table_def_key(const TABLE_LIST *table_list, const char **key)
> # Pointer to list of names of open tables.
> */
>
> -OPEN_TABLE_LIST *list_open_tables(THD *thd, const char *db, const char *wild)
> +struct list_open_tables_arg
> {
> + THD *thd;
> + const char *db;
> + const char *wild;
> TABLE_LIST table_list;
> OPEN_TABLE_LIST **start_list, *open_list;
> - TABLE_SHARE *share;
> - TDC_iterator tdc_it;
> - DBUG_ENTER("list_open_tables");
> +};
>
> - bzero((char*) &table_list,sizeof(table_list));
> - start_list= &open_list;
> - open_list=0;
>
> - tdc_it.init();
> - while ((share= tdc_it.next()))
> +static my_bool list_open_tables_callback(TDC_element *element,
> + list_open_tables_arg *arg)
> {
> - if (db && my_strcasecmp(system_charset_info, db, share->db.str))
> - continue;
> - if (wild && wild_compare(share->table_name.str, wild, 0))
> - continue;
> + char *db= (char*) element->m_key;
> + char *table_name= (char*) element->m_key + strlen((char*) element->m_key) + 1;
>
> + if (arg->db && my_strcasecmp(system_charset_info, arg->db, db))
> + return FALSE;
> + if (arg->wild && wild_compare(table_name, arg->wild, 0))
> + return FALSE;
> +
> /* Check if user has SELECT privilege for any column in the table */
> - table_list.db= share->db.str;
> - table_list.table_name= share->table_name.str;
> - table_list.grant.privilege=0;
> + arg->table_list.db= db;
> + arg->table_list.table_name= table_name;
> + arg->table_list.grant.privilege= 0;
>
> - if (check_table_access(thd,SELECT_ACL,&table_list, TRUE, 1, TRUE))
> - continue;
> + if (check_table_access(arg->thd, SELECT_ACL, &arg->table_list, TRUE, 1, TRUE))
> + return FALSE;
>
> - if (!(*start_list = (OPEN_TABLE_LIST *)
> - sql_alloc(sizeof(**start_list)+share->table_cache_key.length)))
> - {
> - open_list=0; // Out of memory
> - break;
> - }
> + if (!(*arg->start_list= (OPEN_TABLE_LIST *) sql_alloc(
when you know the thd, prefer thd->alloc() over sql_alloc()
(which is, basically, current_thd->alloc())
> + sizeof(**arg->start_list) + element->m_key_length)))
> + return TRUE;
> +
> - strmov((*start_list)->table=
> - strmov(((*start_list)->db= (char*) ((*start_list)+1)),
> - share->db.str)+1,
> - share->table_name.str);
> + strmov((*arg->start_list)->table=
> + strmov(((*arg->start_list)->db= (char*) ((*arg->start_list) + 1)),
> + db) + 1, table_name);
> - (*start_list)->in_use= 0;
> + (*arg->start_list)->in_use= 0;
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - TABLE_SHARE::All_share_tables_list::Iterator it(share->tdc.all_tables);
> +
> + mysql_mutex_lock(&element->LOCK_table_share);
> + TDC_element::All_share_tables_list::Iterator it(element->all_tables);
> TABLE *table;
> while ((table= it++))
> if (table->in_use)
> - ++(*start_list)->in_use;
> + ++(*arg->start_list)->in_use;
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> + mysql_mutex_unlock(&element->LOCK_table_share);
> - (*start_list)->locked= 0; /* Obsolete. */
> + (*arg->start_list)->locked= 0; /* Obsolete. */
> - start_list= &(*start_list)->next;
> + arg->start_list= &(*arg->start_list)->next;
> - *start_list=0;
> + *arg->start_list= 0;
> + return FALSE;
> }
> - tdc_it.deinit();
> - DBUG_RETURN(open_list);
> +
> +
> +OPEN_TABLE_LIST *list_open_tables(THD *thd, const char *db, const char *wild)
> +{
> + list_open_tables_arg argument;
> + DBUG_ENTER("list_open_tables");
> +
> + argument.thd= thd;
> + argument.db= db;
> + argument.wild= wild;
> + bzero((char*) &argument.table_list, sizeof(argument.table_list));
> + argument.start_list= &argument.open_list;
> + argument.open_list= 0;
> +
> + if (tdc_iterate(thd, (my_hash_walk_action) list_open_tables_callback,
> + &argument, true))
> + DBUG_RETURN(0);
> +
> + DBUG_RETURN(argument.open_list);
> }
>
> /*****************************************************************************
> diff --git a/sql/table_cache.cc b/sql/table_cache.cc
> --- a/sql/table_cache.cc
> +++ b/sql/table_cache.cc
> @@ -72,32 +76,23 @@
> /**
> Protects unused shares list.
>
> - TABLE_SHARE::tdc.prev
> - TABLE_SHARE::tdc.next
> - oldest_unused_share
> - end_of_unused_share
> + TDC_element::prev
> + TDC_element::next
> + unused_shares
> */
>
> static mysql_mutex_t LOCK_unused_shares;
> -static mysql_rwlock_t LOCK_tdc; /**< Protects tdc_hash. */
> my_atomic_rwlock_t LOCK_tdc_atomics; /**< Protects tdc_version. */
>
> #ifdef HAVE_PSI_INTERFACE
> -static PSI_mutex_key key_LOCK_unused_shares, key_TABLE_SHARE_LOCK_table_share;
> +PSI_mutex_key key_LOCK_unused_shares, key_TABLE_SHARE_LOCK_table_share;
really? not static?
> static PSI_mutex_info all_tc_mutexes[]=
> {
> { &key_LOCK_unused_shares, "LOCK_unused_shares", PSI_FLAG_GLOBAL },
> { &key_TABLE_SHARE_LOCK_table_share, "TABLE_SHARE::tdc.LOCK_table_share", 0 }
> };
>
> -static PSI_rwlock_key key_rwlock_LOCK_tdc;
> -static PSI_rwlock_info all_tc_rwlocks[]=
> -{
> - { &key_rwlock_LOCK_tdc, "LOCK_tdc", PSI_FLAG_GLOBAL }
> -};
> -
> -
> -static PSI_cond_key key_TABLE_SHARE_COND_release;
> +PSI_cond_key key_TABLE_SHARE_COND_release;
and here
> static PSI_cond_info all_tc_conds[]=
> {
> { &key_TABLE_SHARE_COND_release, "TABLE_SHARE::tdc.COND_release", 0 }
> @@ -265,85 +269,41 @@ void tc_add_table(THD *thd, TABLE *table)
>
> if (need_purge)
> {
> - TABLE_SHARE *purge_share= 0;
> - TABLE_SHARE *share;
> - TABLE *entry;
> - ulonglong UNINIT_VAR(purge_time);
> - TDC_iterator tdc_it;
> + tc_add_table_arg argument;
> + argument.purge_time= ULONGLONG_MAX;
> + tdc_iterate(thd, (my_hash_walk_action) tc_add_table_callback, &argument);
>
> - tdc_it.init();
> - while ((share= tdc_it.next()))
> + if (argument.purge_time != ULONGLONG_MAX)
> {
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - if ((entry= tc_free_tables_back(share)) &&
> - (!purge_share || entry->tc_time < purge_time))
> + TDC_element *element= (TDC_element*) lf_hash_search(&tdc_hash,
> + thd->tdc_hash_pins,
> + argument.key,
> + argument.key_length);
> + if (element)
> {
> - purge_share= share;
> - purge_time= entry->tc_time;
> - }
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> - }
> + TABLE *entry;
> + mysql_mutex_lock(&element->LOCK_table_share);
> + lf_hash_search_unpin(thd->tdc_hash_pins);
> + element->wait_for_mdl_deadlock_detector();
you wait under a mutex? hmm...
>
> - if (purge_share)
> - {
> - mysql_mutex_lock(&purge_share->tdc.LOCK_table_share);
> - tc_wait_for_mdl_deadlock_detector(purge_share);
> - tdc_it.deinit();
> /*
> It may happen that oldest table was acquired meanwhile. In this case
> just go ahead, number of objects in table cache will normalize
> eventually.
> */
> - if ((entry= tc_free_tables_back(purge_share)) &&
> - entry->tc_time == purge_time)
> + if ((entry= element->free_tables_back()) &&
> + entry->tc_time == argument.purge_time)
> {
> - entry->s->tdc.free_tables.remove(entry);
> + element->free_tables.remove(entry);
> tc_remove_table(entry);
> - mysql_mutex_unlock(&purge_share->tdc.LOCK_table_share);
> + mysql_mutex_unlock(&element->LOCK_table_share);
> intern_close_table(entry);
> }
> else
> - mysql_mutex_unlock(&purge_share->tdc.LOCK_table_share);
> + mysql_mutex_unlock(&element->LOCK_table_share);
> }
> - else
> - tdc_it.deinit();
> }
> }
> -
> -
> -/**
> - Acquire TABLE object from table cache.
> -
> - @pre share must be protected against removal.
> -
> - Acquired object cannot be evicted or acquired again.
> -
> - While locked:
> - - pop object from TABLE_SHARE::tdc.free_tables
> -
> - While unlocked:
> - - mark object used by thd
> -
> - @return TABLE object, or NULL if no unused objects.
> -*/
> -
> -static TABLE *tc_acquire_table(THD *thd, TABLE_SHARE *share)
> -{
> - TABLE *table;
> -
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - table= share->tdc.free_tables.pop_front();
> - if (table)
> - {
> - DBUG_ASSERT(!table->in_use);
> - table->in_use= thd;
> - /* The ex-unused table must be fully functional. */
> - DBUG_ASSERT(table->db_stat && table->file);
> - /* The children must be detached from the table. */
> - DBUG_ASSERT(!table->file->extra(HA_EXTRA_IS_ATTACHED_CHILDREN));
> - }
ok, you've moved it to table_cache.h...
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> - return table;
> }
>
>
> @@ -397,88 +357,76 @@ bool tc_release_table(TABLE *table)
> */
> table->in_use= 0;
> /* Add table to the list of unused TABLE objects for this share. */
> - table->s->tdc.free_tables.push_front(table);
> - mysql_mutex_unlock(&table->s->tdc.LOCK_table_share);
> + table->s->tdc->free_tables.push_front(table);
> + mysql_mutex_unlock(&table->s->tdc->LOCK_table_share);
> return false;
>
> purge:
> - tc_wait_for_mdl_deadlock_detector(table->s);
> + table->s->tdc->wait_for_mdl_deadlock_detector();
> tc_remove_table(table);
> - mysql_mutex_unlock(&table->s->tdc.LOCK_table_share);
> + mysql_mutex_unlock(&table->s->tdc->LOCK_table_share);
> table->in_use= 0;
> intern_close_table(table);
> return true;
> }
>
>
> -extern "C" uchar *tdc_key(const uchar *record, size_t *length,
> - my_bool not_used __attribute__((unused)))
> -{
> - TABLE_SHARE *entry= (TABLE_SHARE*) record;
> - *length= entry->table_cache_key.length;
> - return (uchar*) entry->table_cache_key.str;
> -}
> -
> -
> /**
> Delete share from hash and free share object.
> -
> - @return
> - @retval 0 Success
> - @retval 1 Share is referenced
> */
>
> -static int tdc_delete_share_from_hash(TABLE_SHARE *share)
> +static void tdc_delete_share_from_hash(TDC_element *element)
> {
> + THD *thd= current_thd;
> + LF_PINS *pins;
> + TABLE_SHARE *share;
> DBUG_ENTER("tdc_delete_share_from_hash");
> - mysql_rwlock_wrlock(&LOCK_tdc);
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - if (--share->tdc.ref_count)
> - {
> - mysql_cond_broadcast(&share->tdc.COND_release);
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> - mysql_rwlock_unlock(&LOCK_tdc);
> - DBUG_RETURN(1);
> - }
> - my_hash_delete(&tdc_hash, (uchar*) share);
> +
> + share= element->share;
> + DBUG_ASSERT(share);
> + element->share= 0;
> /* Notify PFS early, while still locked. */
"while still locked" what?
> PSI_CALL_release_table_share(share->m_psi);
> share->m_psi= 0;
> - mysql_rwlock_unlock(&LOCK_tdc);
>
> - if (share->tdc.m_flush_tickets.is_empty())
> + if (!element->m_flush_tickets.is_empty())
> {
> - /* No threads are waiting for this share to be flushed, destroy it. */
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> - free_table_share(share);
> - }
> - else
> - {
> - Wait_for_flush_list::Iterator it(share->tdc.m_flush_tickets);
> + Wait_for_flush_list::Iterator it(element->m_flush_tickets);
> Wait_for_flush *ticket;
> while ((ticket= it++))
> (void) ticket->get_ctx()->m_wait.set_status(MDL_wait::GRANTED);
> - /*
> - If there are threads waiting for this share to be flushed,
> - the last one to receive the notification will destroy the
> - share. At this point the share is removed from the table
> - definition cache, so is OK to proceed here without waiting
> - for this thread to do the work.
> - */
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> +
> + do
> + {
> + mysql_cond_wait(&element->COND_release, &element->LOCK_table_share);
> + } while (!element->m_flush_tickets.is_empty());
> }
> - DBUG_RETURN(0);
> +
> + mysql_mutex_unlock(&element->LOCK_table_share);
Ok, so the caller must lock LOCK_table_share?
please put mysql_mutex_assert_owner() in the beginning of the function
> +
> + if (thd)
When thd is NULL here? On shutdown?
> + {
> + fix_thd_pins(thd);
> + pins= thd->tdc_hash_pins;
> }
> + else
> + pins= lf_hash_get_pins(&tdc_hash);
>
> + DBUG_ASSERT(pins); // What can we do about it?
> + element->dbug_release_assertions();
> + lf_hash_delete(&tdc_hash, pins, element->m_key, element->m_key_length);
> + if (!thd)
> + lf_hash_put_pins(pins);
> + free_table_share(share);
> + DBUG_VOID_RETURN;
> +}
>
> +
> /**
> Initialize table definition cache.
> -
> - @retval 0 Success
> - @retval !0 Error
> */
>
> -int tdc_init(void)
> +void tdc_init(void)
> {
> DBUG_ENTER("tdc_init");
> #ifdef HAVE_PSI_INTERFACE
> @@ -642,26 +548,34 @@ void tdc_deinit_share(TABLE_SHARE *share)
> Caller is expected to unlock table share with tdc_unlock_share().
>
> @retval 0 Share not found
> - @retval !0 Pointer to locked table share
> + @retval MY_ERRPTR OOM
> + @retval ptr Pointer to locked table share
> */
>
> -TABLE_SHARE *tdc_lock_share(const char *db, const char *table_name)
> +TDC_element *tdc_lock_share(THD *thd, const char *db, const char *table_name)
> {
> + TDC_element *element;
> char key[MAX_DBKEY_LENGTH];
> - uint key_length;
>
> DBUG_ENTER("tdc_lock_share");
> - key_length= tdc_create_key(key, db, table_name);
> + if (fix_thd_pins(thd))
> + DBUG_RETURN((TDC_element*) MY_ERRPTR);
I suppose you can do it in THD:init, if you'd like. A THD almost always
will need to access table definition cache, so it'll need these pins.
Then there will be no need to return MY_ERRPTR here and handle it in the
caller
>
> - mysql_rwlock_rdlock(&LOCK_tdc);
> - TABLE_SHARE* share= (TABLE_SHARE*) my_hash_search(&tdc_hash,
> - (uchar*) key, key_length);
> - if (share && !share->error)
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - else
> - share= 0;
> - mysql_rwlock_unlock(&LOCK_tdc);
> - DBUG_RETURN(share);
> + element= (TDC_element *) lf_hash_search(&tdc_hash, thd->tdc_hash_pins,
> + (uchar*) key,
> + tdc_create_key(key, db, table_name));
> + if (element)
> + {
> + mysql_mutex_lock(&element->LOCK_table_share);
> + if (!element->share || element->share->error)
> + {
> + mysql_mutex_unlock(&element->LOCK_table_share);
> + element= 0;
> + }
> + lf_hash_search_unpin(thd->tdc_hash_pins);
> + }
> +
> + DBUG_RETURN(element);
Looks good to me
> }
>
>
> @@ -702,60 +616,60 @@ TABLE_SHARE *tdc_acquire_share(THD *thd, const char *db, const char *table_name,
> TABLE **out_table)
> {
> TABLE_SHARE *share;
> + TDC_element *element;
> bool was_unused;
> DBUG_ENTER("tdc_acquire_share");
>
> - mysql_rwlock_rdlock(&LOCK_tdc);
> - share= (TABLE_SHARE*) my_hash_search_using_hash_value(&tdc_hash, hash_value,
> - (uchar*) key,
> - key_length);
> - if (!share)
> + if (fix_thd_pins(thd))
> + DBUG_RETURN(0);
> +
> +retry:
> + while (!(element= (TDC_element*) lf_hash_search_using_hash_value(&tdc_hash,
Was lf_hash_search_using_hash_value added in a separate patch?
> + thd->tdc_hash_pins, hash_value, (uchar*) key, key_length)))
> {
> - TABLE_SHARE *new_share;
> - mysql_rwlock_unlock(&LOCK_tdc);
> + TDC_element tmp(key, key_length);
> + int res= lf_hash_insert(&tdc_hash, thd->tdc_hash_pins, (uchar*) &tmp);
>
> - if (!(new_share= alloc_table_share(db, table_name, key, key_length)))
> + if (res == -1)
> DBUG_RETURN(0);
> - new_share->error= OPEN_FRM_OPEN_ERROR;
> + else if (res == 1)
> + continue;
>
> - mysql_rwlock_wrlock(&LOCK_tdc);
> - share= (TABLE_SHARE*) my_hash_search_using_hash_value(&tdc_hash, hash_value,
> - (uchar*) key,
> - key_length);
> - if (!share)
> - {
> - bool need_purge;
> + element= (TDC_element*) lf_hash_search_using_hash_value(&tdc_hash,
> + thd->tdc_hash_pins, hash_value, (uchar*) key, key_length);
> + lf_hash_search_unpin(thd->tdc_hash_pins);
How can you be sure that nobody frees your element after you unpin it?
> + DBUG_ASSERT(element);
> + element->dbug_release_assertions();
>
> - share= new_share;
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - if (my_hash_insert(&tdc_hash, (uchar*) share))
> + if (!(share= alloc_table_share(db, table_name, key, key_length)))
> {
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
> - mysql_rwlock_unlock(&LOCK_tdc);
> - free_table_share(share);
> + lf_hash_delete(&tdc_hash, thd->tdc_hash_pins, key, key_length);
> DBUG_RETURN(0);
> }
> - need_purge= tdc_hash.records > tdc_size;
> - mysql_rwlock_unlock(&LOCK_tdc);
>
> /* note that tdc_acquire_share() *always* uses discovery */
> open_table_def(thd, share, flags | GTS_USE_DISCOVERY);
> - share->tdc.ref_count++;
> - mysql_mutex_unlock(&share->tdc.LOCK_table_share);
>
> if (share->error)
> {
> - tdc_delete_share_from_hash(share);
> + free_table_share(share);
> + lf_hash_delete(&tdc_hash, thd->tdc_hash_pins, key, key_length);
> DBUG_RETURN(0);
> }
> - else if (need_purge)
> +
> + mysql_mutex_lock(&element->LOCK_table_share);
> + element->share= share;
> + share->tdc= element;
> + element->ref_count++;
> + element->version= tdc_refresh_version();
> + element->flushed= false;
> + mysql_mutex_unlock(&element->LOCK_table_share);
> +
> tdc_purge(false);
> if (out_table)
> *out_table= 0;
> share->m_psi= PSI_CALL_get_table_share(false, share);
> goto end;
> - }
> - free_table_share(new_share);
> }
>
> /* cannot force discovery of a cached share */
> @@ -763,18 +677,25 @@ TABLE_SHARE *tdc_acquire_share(THD *thd, const char *db, const char *table_name,
>
> if (out_table && (flags & GTS_TABLE))
> {
> - if ((*out_table= tc_acquire_table(thd, share)))
> + if ((*out_table= element->acquire_table(thd)))
> {
> - mysql_rwlock_unlock(&LOCK_tdc);
> + lf_hash_search_unpin(thd->tdc_hash_pins);
what this lf_hash_search_unpin corresponds to?
> DBUG_ASSERT(!(flags & GTS_NOLOCK));
> - DBUG_ASSERT(!share->error);
> - DBUG_ASSERT(!share->is_view);
> - DBUG_RETURN(share);
> + DBUG_ASSERT(element->share);
> + DBUG_ASSERT(!element->share->error);
> + DBUG_ASSERT(!element->share->is_view);
> + DBUG_RETURN(element->share);
> }
> }
>
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - mysql_rwlock_unlock(&LOCK_tdc);
> + mysql_mutex_lock(&element->LOCK_table_share);
> + if (!(share= element->share))
> + {
> + mysql_mutex_unlock(&element->LOCK_table_share);
> + lf_hash_search_unpin(thd->tdc_hash_pins);
and here
> + goto retry;
> + }
> + lf_hash_search_unpin(thd->tdc_hash_pins);
may be that first lf_hash_search_unpin was wrong?
the one that goes directly after lf_hash_search.
>
> /*
> We found an existing table definition. Return it if we didn't get
> @@ -983,13 +864,36 @@ bool tdc_remove_table(THD *thd, enum_tdc_remove_table_type remove_type,
> thd->mdl_context.is_lock_owner(MDL_key::TABLE, db, table_name,
> MDL_EXCLUSIVE));
>
> - if ((share= tdc_delete_share(db, table_name)))
> +
> + mysql_mutex_lock(&LOCK_unused_shares);
> + if (!(element= tdc_lock_share(thd, db, table_name)))
> {
> - I_P_List <TABLE, TABLE_share> purge_tables;
> - uint my_refs= 1;
> + mysql_mutex_unlock(&LOCK_unused_shares);
> + DBUG_ASSERT(remove_type != TDC_RT_REMOVE_NOT_OWN_KEEP_SHARE);
> + DBUG_RETURN(false);
> + }
>
> - mysql_mutex_lock(&share->tdc.LOCK_table_share);
> - tc_wait_for_mdl_deadlock_detector(share);
> + DBUG_ASSERT(element != MY_ERRPTR); // What can we do about it?
allocate thd->tdc_hash_pins in THD::init
> +
> + if (!element->ref_count)
> + {
> + if (element->prev)
> + {
> + unused_shares.remove(element);
> + /* Concurrent thread may start using share again, reset prev and next. */
What concurrent thread? element->ref_count is 0, you removed
the the share from the unused_shares list. There can be no concurrent
threads, as far as I understand. And indeed, you do remove the share
from the hash (which does free_table_share) immediately below,
which also proves that there can be no concurrent threads.
> + element->prev= 0;
> + element->next= 0;
> + }
> + mysql_mutex_unlock(&LOCK_unused_shares);
> +
> + tdc_delete_share_from_hash(element);
> + DBUG_RETURN(true);
> + }
> + mysql_mutex_unlock(&LOCK_unused_shares);
> +
> + element->ref_count++;
> +
> + element->wait_for_mdl_deadlock_detector();
> /*
> Mark share flushed in order to ensure that it gets
> automatically deleted once it is no longer referenced.
Regards,
Sergei
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