on SHOW CREATE TRIGGER + MERGE table
Problem: SHOW CREATE TRIGGER erroneously relies on fact
that we have the only underlying table for a trigger
(wrong for merge tables).
Fix: remove erroneous assert().
A REPLACE in the MERGE engine is actually a REPLACE
into one (FIRST or LAST) of the underlying MyISAM
tables. So in effect the server works on the meta
data of the MERGE table, while the real insert happens
in the MyISAM table.
The MERGE table has no index, while MyISAM has a
unique index. When a REPLACE into a MERGE table (
and the REPLACE conflicts with a duplicate in a
child table) is done, we try to access the duplicate
key information for the MERGE table. This information
actually does not exist, hence this results in a crash.
The problem can be resolved by modifying the MERGE
engine to provide us the duplicate key information
directly, instead of just returning the MyISAM index
number as the error key. Then the SQL layer (or "the
server") does not try to access the key_info of the
MERGE table, which does not exist.
The current patch modifies the MERGE engine to provide
the position for a record where a unique key violation
occurs.
table
The MERGE table storage engine does not support the HA_CAN_SQL_HANDLE feature
and any attempt to open the merge table will fail with ER_ILLEGAL_HA.
After an error occurred the tables that was opened must be closed again
or they will be left in an inconsistent state. However, the assumption
made in the code for closing and register handler tables was that only
one table will be opened, and this is not true for MERGE tables which
will cause multiple tables to open.
The next time a SELECT operation was issued on the merge table it
caused the system to freeze.
This patch fixes this issue by making sure that all tables which
are opened also are closed in the event of an error.
and base tables
myrg_attach_children() could reuse a buffer that was allocated
previously based on a definition of a child table. The problem
was that the child's definition might have been changed, so
reusing the buffer could lead to crashes or valgrind errors
under some circumstances.
Fixed by changing myrg_attach_children() so that the
rec_per_key_part buffer is reused only when the child table
have not changed, and reallocated otherwise (the old buffer is
deallocated if necessary).
using it.
The crash was due to a null pointer present for select_lex while
processing the view.
Adding a check while opening the view to see if its a child of a
merge table fixed this problem.
This problem comes while inserting a duplicate row in merge table
without key but the child table has a primary key.
While forming the error message handler tries to locate the key field
which is creating this problem but as there is no key on the merge
table there is a segmentation fault.
A Query in the MyISAM merge table was crashing
if the index merge algorithm was being used
Index Merge optimization requires the reading of
multiple indexes at the same time. Reading multiple
indexes at once with current SE API means that we
need to have handler instance for each to-be-read
index. This is done by creating clones of the handlers
instances. The clone internally does a open of the handler.
The open for a MERGE engine is handled in the following
phases
1) open parent table
2) generate list of underlying
table
3) attach underlying tables
But the current implementation does only the first
phase (i.e.) open parent table.
The current patch fixes this at the MERGE engine level,
by handling the clone operation within the MERGE engine
rather than in the storage engine API. It opens and
attaches the MyISAM tables on the MyISAM storage engine
interface directly within the MERGE engine. The new MyISAM
table instances, as well as the MERGE clone itself, are not
visible in the table cache. This is not a problem because
all locking is handled by the original MERGE table from which
this is cloned of.
Every subsequent query to a merge table with indexes was lowering
down cardinality.
The problem was that key statistics was not cleared when merge
children were detached. Causing next attach children perform
incremental key statistics calculation.
Fixed by clearing key statistics when attaching first child.
Accessing well defined MERGE table may return an error
stating that the merge table is incorrectly defined. This
happens if MERGE child tables were accessed before and we
failed to open another incorrectly defined MERGE table in
this connection.
myrg_open() internally used my_errno as a variable for determining
failure, and thus could be tricked into a wrong decision by other
uses of my_errno.
With this fix we use function local boolean flag instead of my_errno
to determine failure.
for ENGINE=MRG_MYISAM (should be optimized out).
Before WL#3281 MERGE engine had the HA_NOT_EXACT_COUNT flag
unset, and it worked with COUNT optimization as desired.
After the removal of the HA_NOT_EXACT_COUNT flag neither
HA_STATS_RECORDS_IS_EXACT (opposite to former HA_NOT_EXACT_COUNT
flag) nor modern HA_HAS_RECORDS flag were not added to MERGE
table flag mask.
1. The HA_HAS_RECORDS table flag has been set.
2. The ha_myisammrg::records method has been overridden to
calculate total number of records in underlying tables.
When there are no underlying tables specified for a merge table,
SHOW CREATE TABLE outputs a statement that cannot be executed. The
same is true for mysqldump (it generates dumps that cannot be
executed).
This happens because SQL parser does not accept empty UNION() clause.
This patch changes the following:
- it is now possible to execute CREATE/ALTER statement with
empty UNION() clause.
- the same as above, but still worth noting: it is now possible to
remove underlying tables mapping using ALTER TABLE ... UNION=().
- SHOW CREATE TABLE does not output UNION() clause if there are
no underlying tables specified for a merge table. This makes
mysqldump slightly smaller.
self-join
When doing DELETE with self-join on a MyISAM or MERGE table, it could
happen that a record being retrieved in join_read_next_same() has
already been deleted by previous iterations. That caused the engine's
index_next_same() method to fail with HA_ERR_RECORD_DELETED error and
the whole DELETE query to be aborted with an error.
Fixed by suppressing the HA_ERR_RECORD_DELETED error in
hy_myisam::index_next_same() and ha_myisammrg::index_next_same(). Since
HA_ERR_RECORD_DELETED can only be returned by MyISAM, there is no point
in filtering this error in the SQL layer.
corrupts a MERGE table
Bug 26867 - LOCK TABLES + REPAIR + merge table result in
memory/cpu hogging
Bug 26377 - Deadlock with MERGE and FLUSH TABLE
Bug 25038 - Waiting TRUNCATE
Bug 25700 - merge base tables get corrupted by
optimize/analyze/repair table
Bug 30275 - Merge tables: flush tables or unlock tables
causes server to crash
Bug 19627 - temporary merge table locking
Bug 27660 - Falcon: merge table possible
Bug 30273 - merge tables: Can't lock file (errno: 155)
The problems were:
Bug 26379 - Combination of FLUSH TABLE and REPAIR TABLE
corrupts a MERGE table
1. A thread trying to lock a MERGE table performs busy waiting while
REPAIR TABLE or a similar table administration task is ongoing on
one or more of its MyISAM tables.
2. A thread trying to lock a MERGE table performs busy waiting until all
threads that did REPAIR TABLE or similar table administration tasks
on one or more of its MyISAM tables in LOCK TABLES segments do UNLOCK
TABLES. The difference against problem #1 is that the busy waiting
takes place *after* the administration task. It is terminated by
UNLOCK TABLES only.
3. Two FLUSH TABLES within a LOCK TABLES segment can invalidate the
lock. This does *not* require a MERGE table. The first FLUSH TABLES
can be replaced by any statement that requires other threads to
reopen the table. In 5.0 and 5.1 a single FLUSH TABLES can provoke
the problem.
Bug 26867 - LOCK TABLES + REPAIR + merge table result in
memory/cpu hogging
Trying DML on a MERGE table, which has a child locked and
repaired by another thread, made an infinite loop in the server.
Bug 26377 - Deadlock with MERGE and FLUSH TABLE
Locking a MERGE table and its children in parent-child order
and flushing the child deadlocked the server.
Bug 25038 - Waiting TRUNCATE
Truncating a MERGE child, while the MERGE table was in use,
let the truncate fail instead of waiting for the table to
become free.
Bug 25700 - merge base tables get corrupted by
optimize/analyze/repair table
Repairing a child of an open MERGE table corrupted the child.
It was necessary to FLUSH the child first.
Bug 30275 - Merge tables: flush tables or unlock tables
causes server to crash
Flushing and optimizing locked MERGE children crashed the server.
Bug 19627 - temporary merge table locking
Use of a temporary MERGE table with non-temporary children
could corrupt the children.
Temporary tables are never locked. So we do now prohibit
non-temporary chidlren of a temporary MERGE table.
Bug 27660 - Falcon: merge table possible
It was possible to create a MERGE table with non-MyISAM children.
Bug 30273 - merge tables: Can't lock file (errno: 155)
This was a Windows-only bug. Table administration statements
sometimes failed with "Can't lock file (errno: 155)".
These bugs are fixed by a new implementation of MERGE table open.
When opening a MERGE table in open_tables() we do now add the
child tables to the list of tables to be opened by open_tables()
(the "query_list"). The children are not opened in the handler at
this stage.
After opening the parent, open_tables() opens each child from the
now extended query_list. When the last child is opened, we remove
the children from the query_list again and attach the children to
the parent. This behaves similar to the old open. However it does
not open the MyISAM tables directly, but grabs them from the already
open children.
When closing a MERGE table in close_thread_table() we detach the
children only. Closing of the children is done implicitly because
they are in thd->open_tables.
For more detail see the comment at the top of ha_myisammrg.cc.
Changed from open_ltable() to open_and_lock_tables() in all places
that can be relevant for MERGE tables. The latter can handle tables
added to the list on the fly. When open_ltable() was used in a loop
over a list of tables, the list must be temporarily terminated
after every table for open_and_lock_tables().
table_list->required_type is set to FRMTYPE_TABLE to avoid open of
special tables. Handling of derived tables is suppressed.
These details are handled by the new function
open_n_lock_single_table(), which has nearly the same signature as
open_ltable() and can replace it in most cases.
In reopen_tables() some of the tables open by a thread can be
closed and reopened. When a MERGE child is affected, the parent
must be closed and reopened too. Closing of the parent is forced
before the first child is closed. Reopen happens in the order of
thd->open_tables. MERGE parents do not attach their children
automatically at open. This is done after all tables are reopened.
So all children are open when attaching them.
Special lock handling like mysql_lock_abort() or mysql_lock_remove()
needs to be suppressed for MERGE children or forwarded to the parent.
This depends on the situation. In loops over all open tables one
suppresses child lock handling. When a single table is touched,
forwarding is done.
Behavioral changes:
===================
This patch changes the behavior of temporary MERGE tables.
Temporary MERGE must have temporary children.
The old behavior was wrong. A temporary table is not locked. Hence
even non-temporary children were not locked. See
Bug 19627 - temporary merge table locking.
You cannot change the union list of a non-temporary MERGE table
when LOCK TABLES is in effect. The following does *not* work:
CREATE TABLE m1 ... ENGINE=MRG_MYISAM ...;
LOCK TABLES t1 WRITE, t2 WRITE, m1 WRITE;
ALTER TABLE m1 ... UNION=(t1,t2) ...;
However, you can do this with a temporary MERGE table.
You cannot create a MERGE table with CREATE ... SELECT, neither
as a temporary MERGE table, nor as a non-temporary MERGE table.
CREATE TABLE m1 ... ENGINE=MRG_MYISAM ... SELECT ...;
Gives error message: table is not BASE TABLE.
This patch adds cost estimation for the queries with ORDER BY / GROUP BY
and LIMIT.
If there was a ref/range access to the table whose rows were required
to be ordered in the result set the optimizer always employed this access
though a scan by a different index that was compatible with the required
order could be cheaper to produce the first L rows of the result set.
Now for such queries the optimizer makes a choice between the cheapest
ref/range accesses not compatible with the given order and index scans
compatible with it.
SHOW CREATE TABLE fails
Underlying table names, that merge engine fails to open were not
reported.
With this fix CHECK TABLE issued against merge table reports all
underlying table names that it fails to open. Other statements
are unaffected, that is underlying table names are not included
into error message.
This fix doesn't solve SHOW CREATE TABLE issue.
MERGE engine may return incorrect values when several representations
of equal keys are present in the index. For example "groß" and "gross"
or "gross" and "gross " (trailing space), which are considered equal,
but have different lengths.
The problem was that key length was not recalculated after key lookup.
Only MERGE engine is affected.
differences in tables
Certain merge tables were wrongly reported as having incorrect definition:
- Some fields that are 1 byte long (e.g. TINYINT, CHAR(1)), might
be internally casted (in certain cases) to a different type on a
storage engine layer. (affects 4.1 and up)
- If tables in a merge (and a MERGE table itself) had short VARCHAR column (less
than 4 bytes) and at least one (but not all) tables were ALTER'ed (even to an
identical table: ALTER TABLE xxx ENGINE=yyy), table definitions went ouf of
sync. (affects 4.1 only)
This is fixed by relaxing a check for underlying conformance and setting
field type to FIELD_TYPE_STRING in case varchar is shorter than 4
when a table is created.
Using INSERT DELAYED on MERGE tables could lead to table
corruptions.
The manual lists a couple of storage engines, which can be
used with INSERT DELAYED. MERGE is not in this list.
The attempt to try it anyway has not been rejected yet.
This bug was not detected earlier as it can work under
special circumstances. Most notable is low concurrency.
To be safe, this patch rejects any attempt to use INSERT
DELAYED on MERGE tables.
When a merge table is opened compare column and key definition of
underlying tables against column and key definition of merge table.
If any of underlying tables have different column/key definition
refuse to open merge table.
strings
MySQL is setting the flag HA_END_SPACE_KEYS for all the keys that reference
text or varchar columns with collation different than binary.
This was done to handle correctly the situation where a lookup on such a key
may return more than 1 row because of the presence of many rows that differ
only by the amount of trailing space in the table's string column.
Inserting such values however appears to violate the unique checks on
INSERT/UPDATE. Thus that flag must not be set as it will prevent the optimizer
from choosing a faster access method.
This fix removes the setting of the HA_END_SPACE_KEYS flag.
