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Fix for:

Browse Source 
Bug #20662 "Infinite loop in CREATE TABLE IF NOT EXISTS ... SELECT
              with locked tables"
  Bug #20903 "Crash when using CREATE TABLE .. SELECT and triggers"
  Bug #24738 "CREATE TABLE ... SELECT is not isolated properly"
  Bug #24508 "Inconsistent results of CREATE TABLE ... SELECT when
              temporary table exists"
 
Deadlock occured when one tried to execute CREATE TABLE IF NOT
EXISTS ... SELECT statement under LOCK TABLES which held
read lock on target table.
Attempt to execute the same statement for already existing
target table with triggers caused server crashes.
Also concurrent execution of CREATE TABLE ... SELECT statement
and other statements involving target table suffered from
various races (some of which might've led to deadlocks).
Finally, attempt to execute CREATE TABLE ... SELECT in case
when a temporary table with same name was already present
led to the insertion of data into this temporary table and
creation of empty non-temporary table.
 
All above problems stemmed from the old implementation of CREATE
TABLE ... SELECT in which we created, opened and locked target
table without any special protection in a separate step and not
with the rest of tables used by this statement.
This underminded deadlock-avoidance approach used in server
and created window for races. It also excluded target table
from prelocking causing problems with trigger execution.
  
The patch solves these problems by implementing new approach to
handling of CREATE TABLE ... SELECT for base tables.
We try to open and lock table to be created at the same time as
the rest of tables used by this statement. If such table does not
exist at this moment we create and place in the table cache special
placeholder for it which prevents its creation or any other usage
by other threads.

We still use old approach for creation of temporary tables.

Also note that we decided to postpone introduction of some tests
for concurrent behaviour of CREATE TABLE ... SELECT till 5.1.
The main reason for this is absence in 5.0 ability to set @@debug
variable at runtime, which can be circumvented only by using several
test files with individual .opt files. Since the latter is likely
to slowdown test-suite unnecessary we chose not to push this tests
into 5.0, but run them manually for this version and later push
their optimized version into 5.1
This commit is contained in:
dlenev@mockturtle.local
2007-05-11 20:33:13 +04:00
parent 4b0d37362b
commit 8b93e52e92
15 changed files with 918 additions and 183 deletions
Download Patch File Download Diff File Expand all files Collapse all files

420
sql/sql_base.cc
View File

@ -94,6 +94,8 @@ static bool open_new_frm(THD *thd, const char *path, const char *alias,
uint db_stat, uint prgflag,
uint ha_open_flags, TABLE *outparam,
TABLE_LIST *table_desc, MEM_ROOT *mem_root);
static void close_old_data_files(THD *thd, TABLE *table, bool morph_locks,
bool send_refresh);
extern "C" byte *table_cache_key(const byte *record,uint *length,
my_bool not_used __attribute__((unused)))
@ -374,7 +376,21 @@ bool close_cached_tables(THD *thd, bool if_wait_for_refresh,
for (uint idx=0 ; idx < open_cache.records ; idx++)
{
TABLE *table=(TABLE*) hash_element(&open_cache,idx);
if ((table->s->version) < refresh_version && table->db_stat)
/*
Note that we wait here only for tables which are actually open, and
not for placeholders with TABLE::open_placeholder set. Waiting for
latter will cause deadlock in the following scenario, for example:
conn1: lock table t1 write;
conn2: lock table t2 write;
conn1: flush tables;
conn2: flush tables;
It also does not make sense to wait for those of placeholders that
are employed by CREATE TABLE as in this case table simply does not
exist yet.
*/
if (table->needs_reopen_or_name_lock() && table->db_stat)
{
found=1;
DBUG_PRINT("signal", ("Waiting for COND_refresh"));
@ -616,10 +632,10 @@ bool close_thread_table(THD *thd, TABLE **table_ptr)
TABLE *table= *table_ptr;
DBUG_ENTER("close_thread_table");
DBUG_ASSERT(table->key_read == 0);
DBUG_ASSERT(table->file->inited == handler::NONE);
DBUG_ASSERT(!table->file || table->file->inited == handler::NONE);
*table_ptr=table->next;
if (table->s->version != refresh_version ||
if (table->needs_reopen_or_name_lock() ||
thd->version != refresh_version || !table->db_stat)
{
VOID(hash_delete(&open_cache,(byte*) table));
@ -627,6 +643,12 @@ bool close_thread_table(THD *thd, TABLE **table_ptr)
}
else
{
/*
Open placeholders have TABLE::db_stat set to 0, so they should be
handled by the first alternative.
*/
DBUG_ASSERT(!table->open_placeholder);
if (table->s->flush_version != flush_version)
{
table->s->flush_version= flush_version;
@ -1114,6 +1136,43 @@ TABLE *unlink_open_table(THD *thd, TABLE *list, TABLE *find)
}
/**
@brief Auxiliary routine which closes and drops open table.
@param thd Thread handle
@param table TABLE object for table to be dropped
@param db_name Name of database for this table
@param table_name Name of this table
@note This routine assumes that table to be closed is open only
by calling thread so we needn't wait until other threads
will close the table. Also unless called under implicit or
explicit LOCK TABLES mode it assumes that table to be
dropped is already unlocked. In the former case it will
also remove lock on the table. But one should not rely on
this behaviour as it may change in future.
*/
void drop_open_table(THD *thd, TABLE *table, const char *db_name,
const char *table_name)
{
if (table->s->tmp_table)
close_temporary_table(thd, db_name, table_name);
else
{
enum db_type table_type= table->s->db_type;
VOID(pthread_mutex_lock(&LOCK_open));
/*
unlink_open_table() also tells threads waiting for refresh or close
that something has happened.
*/
thd->open_tables= unlink_open_table(thd, thd->open_tables, table);
quick_rm_table(table_type, db_name, table_name);
VOID(pthread_mutex_unlock(&LOCK_open));
}
}
/*
When we call the following function we must have a lock on
LOCK_open ; This lock will be unlocked on return.
@ -1152,6 +1211,11 @@ void wait_for_refresh(THD *thd)
table_list TABLE_LIST object for table to be open, TABLE_LIST::table
member should point to TABLE object which was used for
name-locking.
link_in TRUE - if TABLE object for table to be opened should be
linked into THD::open_tables list.
FALSE - placeholder used for name-locking is already in
this list so we only need to preserve TABLE::next
pointer.
NOTE
This function assumes that its caller already acquired LOCK_open mutex.
@ -1161,7 +1225,7 @@ void wait_for_refresh(THD *thd)
TRUE - Error
*/
bool reopen_name_locked_table(THD* thd, TABLE_LIST* table_list)
bool reopen_name_locked_table(THD* thd, TABLE_LIST* table_list, bool link_in)
{
TABLE *table= table_list->table;
TABLE_SHARE *share;
@ -1199,12 +1263,33 @@ bool reopen_name_locked_table(THD* thd, TABLE_LIST* table_list)
share= table->s;
share->db= share->table_cache_key;
share->key_length=key_length;
/*
We want to prevent other connections from opening this table until end
of statement as it is likely that modifications of table's metadata are
not yet finished (for example CREATE TRIGGER have to change .TRG file,
or we might want to drop table if CREATE TABLE ... SELECT fails).
This also allows us to assume that no other connection will sneak in
before we will get table-level lock on this table.
*/
share->version=0;
share->flush_version=0;
table->in_use = thd;
check_unused();
table->next = thd->open_tables;
thd->open_tables = table;
if (link_in)
{
table->next= thd->open_tables;
thd->open_tables= table;
}
else
{
/*
TABLE object should be already in THD::open_tables list so we just
need to set TABLE::next correctly.
*/
table->next= orig_table.next;
}
table->tablenr=thd->current_tablenr++;
table->used_fields=0;
table->const_table=0;
@ -1216,6 +1301,167 @@ bool reopen_name_locked_table(THD* thd, TABLE_LIST* table_list)
}
/**
@brief Create and insert into table cache placeholder for table
which will prevent its opening (or creation) (a.k.a lock
table name).
@param thd Thread context
@param key Table cache key for name to be locked
@param key_length Table cache key length
@return Pointer to TABLE object used for name locking or 0 in
case of failure.
*/
TABLE *table_cache_insert_placeholder(THD *thd, const char *key,
uint key_length)
{
TABLE *table;
char *key_buff;
DBUG_ENTER("table_cache_insert_placeholder");
safe_mutex_assert_owner(&LOCK_open);
/*
Create a table entry with the right key and with an old refresh version
Note that we must use my_multi_malloc() here as this is freed by the
table cache
*/
if (!my_multi_malloc(MYF(MY_WME | MY_ZEROFILL),
&table, sizeof(*table),
&key_buff, key_length,
NULL))
DBUG_RETURN(NULL);
table->s= &table->share_not_to_be_used;
memcpy(key_buff, key, key_length);
table->s->table_cache_key= key_buff;
table->s->db= table->s->table_cache_key;
table->s->table_name= table->s->table_cache_key + strlen(table->s->db) + 1;
table->s->key_length= key_length;
table->in_use= thd;
table->locked_by_name= 1;
if (my_hash_insert(&open_cache, (byte*)table))
{
my_free((gptr) table, MYF(0));
DBUG_RETURN(NULL);
}
DBUG_RETURN(table);
}
/**
@brief Check if table cache contains an open placeholder for the
table and if this placeholder was created by another thread.
@param thd Thread context
@param db Name of database for table in question
@param table_name Table name
@note The presence of open placeholder indicates that either some
other thread is trying to create table in question and obtained
an exclusive name-lock on it or that this table already exists
and is being flushed at the moment.
@note One should acquire LOCK_open mutex before calling this function.
@note This function is a hack which was introduced in 5.0 only to
minimize code changes. It doesn't present in 5.1.
@retval TRUE Table cache contains open placeholder for the table
which was created by some other thread.
@retval FALSE Otherwise.
*/
bool table_cache_has_open_placeholder(THD *thd, const char *db,
const char *table_name)
{
char key[MAX_DBKEY_LENGTH];
uint key_length;
HASH_SEARCH_STATE state;
TABLE *search;
DBUG_ENTER("table_cache_has_open_placeholder");
safe_mutex_assert_owner(&LOCK_open);
key_length=(uint) (strmov(strmov(key,db)+1,table_name)-key)+1;
for (search= (TABLE*) hash_first(&open_cache, (byte*) key, key_length,
&state);
search ;
search= (TABLE*) hash_next(&open_cache, (byte*) key, key_length,
&state))
{
if (search->in_use == thd)
continue;
if (search->open_placeholder)
DBUG_RETURN(1);
}
DBUG_RETURN(0);
}
/**
@brief Check that table exists on disk or in some storage engine.
@param thd Thread context
@param table Table list element
@param exists[out] Out parameter which is set to TRUE if table
exists and to FALSE otherwise.
@note This function assumes that caller owns LOCK_open mutex.
It also assumes that the fact that there are no name-locks
on the table was checked beforehand.
@note If there is no .FRM file for the table but it exists in one
of engines (e.g. it was created on another node of NDB cluster)
this function will fetch and create proper .FRM file for it.
@retval TRUE Some error occured
@retval FALSE No error. 'exists' out parameter set accordingly.
*/
bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists)
{
char path[FN_REFLEN];
int rc;
DBUG_ENTER("check_if_table_exists");
safe_mutex_assert_owner(&LOCK_open);
*exists= TRUE;
build_table_path(path, sizeof(path), table->db, table->table_name, reg_ext);
if (!access(path, F_OK))
DBUG_RETURN(FALSE);
/* .FRM file doesn't exist. Check if some engine can provide it. */
rc= ha_create_table_from_engine(thd, table->db, table->table_name);
if (rc < 0)
{
/* Table does not exists in engines as well. */
*exists= FALSE;
DBUG_RETURN(FALSE);
}
else if (!rc)
{
/* Table exists in some engine and .FRM for it was created. */
DBUG_RETURN(FALSE);
}
else /* (rc > 0) */
{
my_printf_error(ER_UNKNOWN_ERROR, "Failed to open '%-.64s', error while "
"unpacking from engine", MYF(0), table->table_name);
DBUG_RETURN(TRUE);
}
}
/*
Open a table.
@ -1231,12 +1477,17 @@ bool reopen_name_locked_table(THD* thd, TABLE_LIST* table_list)
MYSQL_LOCK_IGNORE_FLUSH - Open table even if
someone has done a flush or namelock on it.
No version number checking is done.
MYSQL_OPEN_IGNORE_LOCKED_TABLES - Open table
ignoring set of locked tables and prelocked mode.
MYSQL_OPEN_TEMPORARY_ONLY - Open only temporary
table not the base table or view.
IMPLEMENTATION
Uses a cache of open tables to find a table not in use.
If table list element for the table to be opened has "create" flag
set and table does not exist, this function will automatically insert
a placeholder for exclusive name lock into the open tables cache and
will return the TABLE instance that corresponds to this placeholder.
RETURN
NULL Open failed. If refresh is set then one should close
all other tables and retry the open.
@ -1305,6 +1556,12 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
}
}
if (flags & MYSQL_OPEN_TEMPORARY_ONLY)
{
my_error(ER_NO_SUCH_TABLE, MYF(0), table_list->db, table_list->table_name);
DBUG_RETURN(0);
}
/*
The table is not temporary - if we're in pre-locked or LOCK TABLES
mode, let's try to find the requested table in the list of pre-opened
@ -1312,8 +1569,7 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
open not pre-opened tables in pre-locked/LOCK TABLES mode.
TODO: move this block into a separate function.
*/
if (!(flags & MYSQL_OPEN_IGNORE_LOCKED_TABLES) &&
(thd->locked_tables || thd->prelocked_mode))
if (thd->locked_tables || thd->prelocked_mode)
{ // Using table locks
TABLE *best_table= 0;
int best_distance= INT_MIN;
@ -1495,7 +1751,7 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
c1: name lock t2; -- blocks
c2: open t1; -- blocks
*/
if (table->s->version != refresh_version)
if (table->needs_reopen_or_name_lock())
{
DBUG_PRINT("note",
("Found table '%s.%s' with different refresh version",
@ -1507,6 +1763,14 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
continue;
}
/* Avoid self-deadlocks by detecting self-dependencies. */
if (table->open_placeholder && table->in_use == thd)
{
VOID(pthread_mutex_unlock(&LOCK_open));
my_error(ER_UPDATE_TABLE_USED, MYF(0), table->s->table_name);
DBUG_RETURN(0);
}
/*
Back off, part 1: mark the table as "unused" for the
purpose of name-locking by setting table->db_stat to 0. Do
@ -1523,6 +1787,14 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
and wait till the operation is complete: when any
operation that juggles with table->s->version completes,
it broadcasts COND_refresh condition variable.
If 'old' table we met is in use by current thread we return
without waiting since in this situation it's this thread
which is responsible for broadcasting on COND_refresh
(and this was done already in close_old_data_files()).
Good example of such situation is when we have statement
that needs two instances of table and FLUSH TABLES comes
after we open first instance but before we open second
instance.
*/
if (table->in_use != thd)
{
@ -1564,6 +1836,40 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
while (open_cache.records > table_cache_size && unused_tables)
VOID(hash_delete(&open_cache,(byte*) unused_tables)); /* purecov: tested */
if (table_list->create)
{
bool exists;
if (check_if_table_exists(thd, table_list, &exists))
{
VOID(pthread_mutex_unlock(&LOCK_open));
DBUG_RETURN(NULL);
}
if (!exists)
{
/*
Table to be created, so we need to create placeholder in table-cache.
*/
if (!(table= table_cache_insert_placeholder(thd, key, key_length)))
{
VOID(pthread_mutex_unlock(&LOCK_open));
DBUG_RETURN(NULL);
}
/*
Link placeholder to the open tables list so it will be automatically
removed once tables are closed. Also mark it so it won't be ignored
by other trying to take name-lock.
*/
table->open_placeholder= 1;
table->next= thd->open_tables;
thd->open_tables= table;
VOID(pthread_mutex_unlock(&LOCK_open));
DBUG_RETURN(table);
}
/* Table exists. Let us try to open it. */
}
/* make a new table */
if (!(table=(TABLE*) my_malloc(sizeof(*table),MYF(MY_WME))))
{
@ -1794,9 +2100,24 @@ bool close_data_tables(THD *thd,const char *db, const char *table_name)
}
/*
Reopen all tables with closed data files
One should have lock on LOCK_open when calling this
/**
@brief Reopen all tables with closed data files.
@param thd Thread context
@param get_locks Should we get locks after reopening tables ?
@param in_refresh Are we in FLUSH TABLES ? TODO: It seems that
we can remove this parameter.
@note Since this function can't properly handle prelocking and
create placeholders it should be used in very special
situations like FLUSH TABLES or ALTER TABLE. In general
case one should just repeat open_tables()/lock_tables()
combination when one needs tables to be reopened (for
example see open_and_lock_tables()).
@note One should have lock on LOCK_open when calling this.
@return FALSE in case of success, TRUE - otherwise.
*/
bool reopen_tables(THD *thd,bool get_locks,bool in_refresh)
@ -1841,7 +2162,7 @@ bool reopen_tables(THD *thd,bool get_locks,bool in_refresh)
if (in_refresh)
{
table->s->version=0;
table->locked_by_flush=0;
table->open_placeholder= 0;
}
}
}
@ -1867,35 +2188,71 @@ bool reopen_tables(THD *thd,bool get_locks,bool in_refresh)
DBUG_RETURN(error);
}
/*
Close handlers for tables in list, but leave the TABLE structure
intact so that we can re-open these quickly
abort_locks is set if called from flush_tables.
/**
@brief Close handlers for tables in list, but leave the TABLE structure
intact so that we can re-open these quickly.
@param thd Thread context
@param table Head of the list of TABLE objects
@param morph_locks TRUE - remove locks which we have on tables being closed
but ensure that no DML or DDL will sneak in before
we will re-open the table (i.e. temporarily morph
our table-level locks into name-locks).
FALSE - otherwise
@param send_refresh Should we awake waiters even if we didn't close any tables?
*/
void close_old_data_files(THD *thd, TABLE *table, bool abort_locks,
void close_old_data_files(THD *thd, TABLE *table, bool morph_locks,
bool send_refresh)
{
DBUG_ENTER("close_old_data_files");
bool found=send_refresh;
for (; table ; table=table->next)
{
if (table->s->version != refresh_version)
if (table->needs_reopen_or_name_lock())
{
found=1;
if (!abort_locks) // If not from flush tables
/*
Note that it is safe to update version even for open placeholders
as later in this function we reset TABLE::open_placeholder and thus
effectively remove them from the table cache.
*/
if (!morph_locks) // If not from flush tables
table->s->version= refresh_version; // Let other threads use table
if (table->db_stat)
{
if (abort_locks)
{
mysql_lock_abort(thd,table); // Close waiting threads
mysql_lock_remove(thd, thd->locked_tables,table);
table->locked_by_flush=1; // Will be reopened with locks
}
if (morph_locks)
{
/*
Wake up threads waiting for table-level lock on this table
so they won't sneak in when we will temporarily remove our
lock on it. This will also give them a chance to close their
instances of this table.
*/
mysql_lock_abort(thd, table);
mysql_lock_remove(thd, thd->locked_tables, table);
/*
We want to protect the table from concurrent DDL operations
(like RENAME TABLE) until we will re-open and re-lock it.
*/
table->open_placeholder= 1;
}
table->file->close();
table->db_stat=0;
}
else if (table->open_placeholder)
{
/*
We come here only in close-for-back-off scenario. So we have to
"close" create placeholder here to avoid deadlocks (for example,
in case of concurrent execution of CREATE TABLE t1 SELECT * FROM t2
and RENAME TABLE t2 TO t1). In close-for-re-open scenario we will
probably want to let it stay.
*/
DBUG_ASSERT(!morph_locks);
table->open_placeholder= 0;
}
}
}
if (found)
@ -1923,9 +2280,8 @@ bool table_is_used(TABLE *table, bool wait_for_name_lock)
search= (TABLE*) hash_next(&open_cache, (byte*) key,
key_length, &state))
{
if (search->locked_by_flush ||
search->locked_by_name && wait_for_name_lock ||
search->db_stat && search->s->version < refresh_version)
if (search->locked_by_name && wait_for_name_lock ||
search->is_name_opened() && search->needs_reopen_or_name_lock())
return 1; // Table is used
}
} while ((table=table->next));
@ -5661,7 +6017,7 @@ bool remove_table_from_cache(THD *thd, const char *db, const char *table_name,
else if (in_use != thd)
{
in_use->some_tables_deleted=1;
if (table->db_stat)
if (table->is_name_opened())
{
DBUG_PRINT("info", ("Found another active instance of the table"));
result=1;