2630.39.1, 2630.28.29, 2630.34.3, 2630.34.2, 2630.34.1, 2630.29.29,
2630.29.28, 2630.31.1, 2630.28.13, 2630.28.10, 2617.23.14 and
some other minor revisions.
This patch implements:
WL#4264 "Backup: Stabilize Service Interface" -- all the
server prerequisites except si_objects.{h,cc} themselves (they can
be just copied over, when needed).
WL#4435: Support OUT-parameters in prepared statements.
(and all issues in the initial patches for these two
tasks, that were discovered in pushbuild and during testing).
Bug#39519: mysql_stmt_close() should flush all data
associated with the statement.
After execution of a prepared statement, send OUT parameters of the invoked
stored procedure, if any, to the client.
When using the binary protocol, send the parameters in an additional result
set over the wire. When using the text protocol, assign out parameters to
the user variables from the CALL(@var1, @var2, ...) specification.
The following refactoring has been made:
- Protocol::send_fields() was renamed to Protocol::send_result_set_metadata();
- A new Protocol::send_result_set_row() was introduced to incapsulate
common functionality for sending row data.
- Signature of Protocol::prepare_for_send() was changed: this operation
does not need a list of items, the number of items is fully sufficient.
The following backward incompatible changes have been made:
- CLIENT_MULTI_RESULTS is now enabled by default in the client;
- CLIENT_PS_MULTI_RESUTLS is now enabled by default in the client.
include/mysql.h:
Add a new flag to MYSQL_METHODS::flush_use_result
function pointer. This flag determines if all results
should be flushed or only the first one:
- if flush_all_results is TRUE, then cli_flush_use_result()
will read/flush all pending results. I.e. it will read
all packets while server status attribute indicates that
there are more results. This is a new semantic, required
to fix the bug.
- if flush_all_results is FALSE, the old sematic
is preserved -- i.e. cli_flush_use_result() reads data
until first EOF-packet.
include/mysql.h.pp:
Update the ABI with new calls (compatible changes).
include/mysql_com.h:
Add CLIENT_PS_OUT_PARAMS -- a client capability indicating that the client supportsю
libmysql/libmysql.c:
Add mysql_stmt_next_result() -- analogue of mysql_next_result() for binary protocol.
Fix a minor bug in alloc_fields() -- not all members were copied over,
and some only shallow-copied (catalog).
Flush all results in mysql_stmt_close() (Bug#39519).
libmysqld/lib_sql.cc:
Rename send_fields() -> send_result_set_metadata().
Refactoring: change prepare_for_send() so that it accepts only
what it really needs -- a number of elements in the list.
mysql-test/r/ps.result:
Update results: WL#4435.
mysql-test/t/ps.test:
WL#4435: A test case for an SQL-part of the problem.
sql-common/client.c:
Bug#39519.
Implement new functionality in cli_flush_use_result():
if flush_all_delete is TRUE, then it should read/flush
all pending results.
sql/Makefile.am:
Add a new header sql_prepare.h to the list
of build headers.
sql/events.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/handler.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/mysql_priv.h:
Move sql_prepare.cc-specific declarations to a new
header - sql_prepare.h.
sql/procedure.h:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/protocol.cc:
Move the logic responsible for sending of one result
set row to the Protocol class. Define a template
for end-of-statement action.
Refactoring: change prepare_for_send() so that it accepts
only what it really needs -- a number of elements in the list.
Rename send_fields() to send_result_set_metadata().
sql/protocol.h:
Update with new declarations (WL#4435).
Rename send_fields() -> send_result_set_metadata().
prepare_for_send() only needs the number of columns to send,
and doesn't use the item list - update signature to require
only what's needed.
Add a new protocol type -- Protocol_local.
sql/repl_failsafe.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/slave.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_acl.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_base.cc:
Include sql_prepare.h (for Reprepare_observer).
sql/sql_cache.cc:
Extend the query cache flags block to be able
to store a numeric id for the result format,
not just a flag binary/non-binary.
sql/sql_class.cc:
Update to use the rename of Protocol::send_fields()
to Protocol::send_result_set_metadata().
Use Protocol::send_one_result_set_row().
sql/sql_class.h:
Move the declaration of Reprepare_observer to the
new header - sql_prepare.h.
Update to the new signature of class Protocol::send_fields().
sql/sql_connect.cc:
Use a protocol template method instead of
raw NET layer API at the end of a statement.
sql/sql_cursor.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_error.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_handler.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
Use new method Protocol::send_one_result_set_row().
sql/sql_help.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_lex.cc:
Initialize multi_statements variable.
Add a handy constant for empty lex
string.
sql/sql_lex.h:
Add a separate member for a standalone
parsing option - multi-statements support.
sql/sql_list.cc:
sql_list.h is a standalone header now,
no need to include mysql_priv.h.
sql/sql_list.h:
Make sql_list.h a stand-alone header.
sql/sql_parse.cc:
Include sql_prepare.h for prepared
statements- related declarations.
Use a new Protocol template method to end
each statement (send OK, EOF or ERROR to
the client).
sql/sql_prepare.cc:
Implement Execute Direct API (WL#4264),
currently unused. It will be used by the service
interface (Backup).
Use a new header - sql_prepare.h.
Add support for OUT parameters in the
binary and text protocol (prepared statements
only).
sql/sql_prepare.h:
Add a new header to contain (for now)
all prepared statement- external
related declarations.
sql/sql_profile.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_repl.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_select.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_show.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_string.h:
Add a way to convert a String to LEX_STRING.
sql/sql_table.cc:
Rename: Protocol::send_fields() ->
Protocol::send_result_set_metadata().
sql/sql_update.cc:
Remove an extraneous my_error(). The error
is already reported in update_non_unique_table_error().
sql/sql_yacc.yy:
Support for multi-statements is an independent
property of parsing, not derived from
the protocol type.
tests/mysql_client_test.c:
Add tests for WL#4435 (binary protocol).
----------------------------------------------------------
revno: 2630.22.11
committer: Konstantin Osipov <konstantin@mysql.com>
branch nick: mysql-6.0-records
timestamp: Mon 2008-08-11 16:40:09 +0400
message:
Move read_record related functions to a new header - records.h
sql/Makefile.am:
Introduce records.h
sql/handler.h:
Forward-declare class handler (an unnecessary forward declaration
was removed from mysql_priv.h).
sql/item_subselect.cc:
Make read_record function naming more consistent.
Assign read_record function at once, no need to defer till
read_first_record invocation.
sql/mysql_priv.h:
Include records.h, previously part of structs.h
sql/records.cc:
Use records.h
sql/sql_select.h:
Update to use new declarations.
sql/structs.h:
Move declarations of READ_RECORD and related functions to records.h
----------------------------------------------------------
revno: 2630.13.6
committer: Konstantin Osipov <konstantin@mysql.com>
branch nick: mysql-6.0-3288
timestamp: Fri 2008-07-11 20:22:44 +0400
message:
WL#3288, step 1: ensure that the SQL layer always closes an open
cursor (rnd or index read) before closing a handler.
sql/handler.h:
Assert that the read is closed in handler destructor.
sql/sql_select.cc:
Remove JOIN::table which was a piece of redundancy. The problem was
that JOIN::cleanup() works only if JOIN::table is not null,
but JOIN::cleanup also assigns JOIN::table to NULL. This assignment
is apparently there for safety, from the times when we had no support for correlated
subqueries. Indeed, in case of a evaluation of a correlated subquery more than once it led
to JOIN::cleanup doing nothing, and leaving the rnd or index read open.
In do_select(), make sure we call JOIN::join_free() even in case of an
error.
sql/sql_select.h:
Remove JOIN::table, JOIN::all_tables has the same functionality.
Temporary tables may set join->group to 0 even though there is
grouping. Also need to test if sum_func_count>0 when JOIN::exec()
decides whether to present results in a grouped manner.
sql/sql_select.cc:
Temporary tables may set join->group to 0 even though there is
grouping. Also need to test if sum_func_count>0 when JOIN::exec()
decides whether to present results in a grouped manner.
columns without where/group
Simple SELECT with implicit grouping used to return many rows if
the query was ordered by the aggregated column in the SELECT
list. This was incorrect because queries with implicit grouping
should only return a single record.
The problem was that when JOIN:exec() decided if execution needed
to handle grouping, it was assumed that sum_func_count==0 meant
that there were no aggregate functions in the query. This
assumption was not correct in JOIN::exec() because the aggregate
functions might have been optimized away during JOIN::optimize().
The reason why queries without ordering behaved correctly was
that sum_func_count is only recalculated if the optimizer chooses
to use temporary tables (which it does in the ordered case).
Hence, non-ordered queries were correctly treated as grouped.
The fix for this bug was to remove the assumption that
sum_func_count==0 means that there is no need for grouping. This
was done by introducing variable "bool implicit_grouping" in the
JOIN object.
mysql-test/r/func_group.result:
Add test for BUG#47280
mysql-test/t/func_group.test:
Add test for BUG#47280
sql/opt_sum.cc:
Improve comment for opt_sum_query()
sql/sql_class.h:
Add comment for variables in TMP_TABLE_PARAM
sql/sql_select.cc:
Introduce and use variable implicit_grouping instead of (!group_list && sum_func_count) in places that need to test if grouping is required. Also added comments for: optimization of aggregate fields for implicitly grouped queries (JOIN::optimize) and choice of end_select method (JOIN::execute)
sql/sql_select.h:
Add variable implicit_grouping, which will be TRUE for queries that contain aggregate functions but no GROUP BY clause. Also added comment to sort_and_group variable.
local storage for query cache).
We need more than one pointer in a thread to
represent the query cache and net->query_cache_query can not be used
any more (due to ABI compatibility issues and to different life
time of NET and THD).
This is a backport of the following patch from 6.0:
----------------------------------------------------------
revno: 2476.1157.2
committer: kostja@bodhi.(none)
timestamp: Sat 2007-06-16 13:29:24 +0400
include/mysql.h.pp:
Update the ABI (NET::query_cache_query is now unused).
include/mysql_com.h:
NET::query_cache_query is now unused.
sql/mysql_priv.h:
Update signatures of ex-functios now member functions.
sql/sql_cache.cc:
Introduce THD::query_cache_tls.
sql/sql_cache.h:
Introduce THD::query_cache_tls.
sql/sql_class.cc:
Introduce THD::query_cache_tls.
sql/sql_class.h:
Introduce THD::query_cache_tls.
sql/sql_parse.cc:
Use THD::query_cache_tls.
sql/sql_select.cc:
Use THD::query_cache_tls.
buffering is used
FORCE INDEX FOR ORDER BY now prevents the optimizer from
using join buffering. As a result the optimizer can use
indexed access on the first table and doesn't need to
sort the complete resultset at the end of the statement.
the fix is reverted from 5.1, mysql-pe as
unnecessary(no valgrind warnings there).
sql/sql_select.cc:
the fix is reverted from 5.1, mysql-pe as
unnecessary(no valgrind warnings there).
query
The fix for bug 46749 removed the check for OUTER_REF_TABLE_BIT
and substituted it for a check on the presence of
Item_ident::depended_from.
Removing it altogether was wrong : OUTER_REF_TABLE_BIT should
still be checked in addition to depended_from (because it's not
set in all cases and doesn't contradict to the check of depended_from).
Fixed by returning the old condition back as a compliment to the
new one.
The external 'for' loop in remove_dup_with_compare() handled
HA_ERR_RECORD_DELETED by just starting over without advancing
to the next record which caused an infinite loop.
This condition could be triggered on certain data by a SELECT
query containing DISTINCT, GROUP BY and HAVING clauses.
Fixed remove_dup_with_compare() so that we always advance to
the next record when receiving HA_ERR_RECORD_DELETED from
rnd_next().
mysql-test/r/distinct.result:
Added a test case for bug #46159.
mysql-test/t/distinct.test:
Added a test case for bug #46159.
sql/sql_select.cc:
Fixed remove_dup_with_compare() so that we always advance to
the next record when receiving HA_ERR_RECORD_DELETED from
rnd_next().
Memory allocated in TMP_TABLE_PARAM::copy_field is not cleaned up.
The fix is to clean up TMP_TABLE_PARAM::copy_field array in JOIN::destroy.
mysql-test/r/explain.result:
test result
mysql-test/t/explain.test:
test case
sql/sql_select.cc:
Memory allocated in TMP_TABLE_PARAM::copy_field is not cleaned up.
The fix is to clean up TMP_TABLE_PARAM::copy_field array in JOIN::destroy.
function,file sql_base.cc
When uncacheable queries are written to a temp table the optimizer must
preserve the original JOIN structure, because it is re-using the JOIN
structure to read from the resulting temporary table.
This was done only for uncacheable sub-queries.
But top level queries can also benefit from this mechanism, specially if
they're using index access and need a reset.
Fixed by not limiting the saving of JOIN structure to subqueries
exclusively.
Added a new test file to extend the existing (large) subquery.test.
field references
This error requires a combination of factors :
1. An "impossible where" in the outermost SELECT
2. An aggregate in the outermost SELECT
3. A correlated subquery with a WHERE clause that includes an outer
field reference as a top level WHERE sargable predicate
When JOIN::optimize detects an "impossible WHERE" it will bail out
without doing the rest of the work and initializations. It will not
call make_join_statistics() as well. And make_join_statistics fills
in various structures for each table referenced.
When processing the result of the "impossible WHERE" the query must
send a single row of data if there are aggregate functions in it.
In this case the server marks all the aggregates as having received
no rows and calls the relevant Item::val_xxx() method on the SELECT
list. However if this SELECT list happens to contain a correlated
subquery this subquery is evaluated in a normal evaluation mode.
And if this correlated subquery has a reference to a field from the
outermost "impossible where" SELECT the add_key_fields will mistakenly
consider the outer field reference as a "local" field reference when
looking for sargable predicates.
But since the SELECT where the outer field reference refers to is not
completely initialized due to the "impossible WHERE" in this level
we'll get a NULL pointer reference.
Fixed by making a better condition for discovering if a field is "local"
to the SELECT level being processed.
It's not enough to look for OUTER_REF_TABLE_BIT in this case since
for outer references to constant tables the Item_field::used_tables()
will return 0 regardless of whether the field reference is from the
local SELECT or not.
The problem was that creating a DECIMAL column from a decimal
value could lead to a failed assertion as decimal values can
have a higher precision than those attached to a table. The
assert could be triggered by creating a table from a decimal
with a large (> 30) scale. Also, there was a problem in
calculating the number of digits in the integral and fractional
parts if both exceeded the maximum number of digits permitted
by the new decimal type.
The solution is to ensure that truncation procedure is executed
when deducing a DECIMAL column from a decimal value of higher
precision. If the integer part is equal to or bigger than the
maximum precision for the DECIMAL type (65), the integer part
is truncated to fit and the fractional becomes zero. Otherwise,
the fractional part is truncated to fit into the space left
after the integer part is copied.
This patch borrows code and ideas from Martin Hansson's patch.
mysql-test/r/type_newdecimal.result:
Add test case result for Bug#45261. Also, update test case to
reflect that an additive operation increases the precision of
the resulting type by 1.
mysql-test/t/type_newdecimal.test:
Add test case for Bug#45261
sql/field.cc:
Added DBUG_ASSERT to ensure object's invariant is maintained.
Implement method to create a field to hold a decimal value
from an item.
sql/field.h:
Explain member variable. Add method to create a new decimal field.
sql/item.cc:
The precision should only be capped when storing the value
on a table. Also, this makes it impossible to calculate the
integer part if Item::decimals (the scale) is larger than the
precision.
sql/item.h:
Simplify calculation of integer part.
sql/item_cmpfunc.cc:
Do not limit the precision. It will be capped later.
sql/item_func.cc:
Use new method for allocating a new decimal field.
Add a specialized method for retrieving the precision
of a user variable item.
sql/item_func.h:
Add method to return the precision of a user variable.
sql/item_sum.cc:
Use new method for allocating a new decimal field.
sql/my_decimal.h:
The integer part could be improperly calculated for a decimal
with 31 digits in the fractional part.
sql/sql_select.cc:
Use new method which truncates the integer or decimal parts
as needed.
Problem 1:
When the 'Using index' optimization is used, the optimizer may still - after
cost-based optimization - decide to use another index in order to avoid using
a temporary table. But when this happens, the flag to the storage engine to
read index only (not table) was still set. Fixed by resetting the flag in the
storage engine and TABLE structure in the above scenario, unless the new index
allows for the same optimization.
Problem 2:
When a 'ref' access method was employed by cost-based optimizer, (when the column
is non-NULLable), it was assumed that it needed no initialization if 'quick' access
methods (since they are based on range scan). When ORDER BY optimization overrides
the decision, however, it expects to have this initialized and hence crashes.
Fixed in 5.1 (was fixed in 6.0 already) by initializing 'quick' even when there's
'ref' access.
mysql-test/r/order_by.result:
Bug#46454: Test result.
mysql-test/t/order_by.test:
Bug#46454: Test case.
sql/sql_select.cc:
Bug#46454:
Problem 1 fixed in make_join_select()
Problem 2 fixed in test_if_skip_sort_order()
sql/table.h:
Bug#46454: Added comment to field.
bzr branch mysql-5.1-performance-version mysql-trunk # Summit
cd mysql-trunk
bzr merge mysql-5.1-innodb_plugin # which is 5.1 + Innodb plugin
bzr rm innobase # remove the builtin
Next step: build, test fixes.
In create_myisam_from_heap() mark all errors as fatal except
HA_ERR_RECORD_FILE_FULL for a HEAP table.
Not doing so could lead to problems, e.g. in a case when a
temporary MyISAM table gets overrun due to its MAX_ROWS limit
while executing INSERT/REPLACE IGNORE ... SELECT.
The SELECT execution was aborted, but the error was
converted to a warning due to IGNORE clause, so neither 'ok'
nor 'error' packet could be sent back to the client. This
condition led to hanging client when using 5.0 server, or
assertion failure in 5.1.
mysql-test/r/insert_select.result:
Added a test case for bug #46075.
mysql-test/t/insert_select.test:
Added a test case for bug #46075.
sql/sql_select.cc:
In create_myisam_from_heap() mark all errors as fatal except
HA_ERR_RECORD_FILE_FULL for a HEAP table.
use partial primary key if another index can prevent filesort
The fix for bug #28404 causes the covering ordering indexes to be
preferred unconditionally over non-covering and ref indexes.
Fixed by comparing the cost of using a covering index to the cost of
using a ref index even for covering ordering indexes.
Added an assertion to clarify the condition the local variables should
be in.
mysql-test/include/mix1.inc:
Bug #36259: fixed a non-stable test case
mysql-test/r/innodb_mysql.result:
Bug #36259 and #45828 : test case
mysql-test/t/innodb_mysql.test:
Bug #36259 and #45828 : test case
sql/sql_select.cc:
Bug #36259 and #45828 : don't consider covering indexes supperior to
ref keys.
Using DECIMAL constants with more than 65 digits in CREATE
TABLE ... SELECT led to bogus errors in release builds or
assertion failures in debug builds.
The problem was in inconsistency in how DECIMAL constants and
fields are handled internally. We allow arbitrarily long
DECIMAL constants, whereas DECIMAL(M,D) columns are limited to
M<=65 and D<=30. my_decimal_precision_to_length() was used in
both Item and Field code and truncated precision to
DECIMAL_MAX_PRECISION when calculating value length without
adjusting precision and decimals. As a result, a DECIMAL
constant with more than 65 digits ended up having length less
than precision or decimals which led to assertion failures.
Fixed by modifying my_decimal_precision_to_length() so that
precision is truncated to DECIMAL_MAX_PRECISION only for Field
object which is indicated by the new 'truncate' parameter.
Another inconsistency fixed by this patch is how DECIMAL
constants and expressions are handled for CREATE ... SELECT.
create_tmp_field_from_item() (which is used for constants) was
changed as a part of the bugfix for bug #24907 to handle long
DECIMAL constants gracefully. Item_func::tmp_table_field()
(which is used for expressions) on the other hand was still
using a simplistic approach when creating a Field_new_decimal
from a DECIMAL expression.
mysql-test/r/type_newdecimal.result:
Added a test case for bug #45262.
mysql-test/t/type_newdecimal.test:
Added a test case for bug #45262.
sql/item.cc:
Use the new 'truncate' parameter in
my_decimal_precision_to_length().
sql/item_cmpfunc.cc:
Use the new 'truncate' parameter in
my_decimal_precision_to_length().
sql/item_func.cc:
1. Use the new 'truncate' parameter in
my_decimal_precision_to_length().
2. Do not truncate decimal precision to DECIMAL_MAX_PRECISION
for additive expressions involving long DECIMAL constants.
3. Fixed an incosistency in how DECIMAL constants and
expressions are handled for CREATE ... SELECT.
sql/item_func.h:
Use the new 'truncate' parameter in
my_decimal_precision_to_length().
sql/item_sum.cc:
Use the new 'truncate' parameter in
my_decimal_precision_to_length().
sql/my_decimal.h:
Do not truncate precision to DECIMAL_MAX_PRECISION
when calculating length in
my_decimal_precision_to_length() if 'truncate' parameter
is FALSE.
sql/sql_select.cc:
1. Use the new 'truncate' parameter in
my_decimal_precision_to_length().
2. Use a more correct logic when adjusting value's length.
The TABLE::reginfo.impossible_range is used by the optimizer to indicate
that the condition applied to the table is impossible. It wasn't initialized
at table opening and this might lead to an empty result on complex queries:
a query might set the impossible_range flag on a table and when the query finishes,
all tables are returned back to the table cache. The next query that uses the table
with the impossible_range flag set and an index over the table will see the flag
and thus return an empty result.
The open_table function now initializes the TABLE::reginfo.impossible_range
variable.
mysql-test/r/select.result:
A test case for the bug#45266: Uninitialized variable lead to an empty result.
mysql-test/t/select.test:
A test case for the bug#45266: Uninitialized variable lead to an empty result.
sql/sql_base.cc:
Bug#45266: Uninitialized variable lead to an empty result.
The open_table function now initializes the TABLE::reginfo.impossible_range
variable.
sql/sql_select.cc:
Bug#45266: Uninitialized variable lead to an empty result.
The open_table function now initializes the TABLE::reginfo.impossible_range
variable.
sql/structs.h:
Bug#45266: Uninitialized variable lead to an empty result.
A comment is added.
with gcc 4.3.2
Compiling MySQL with gcc 4.3.2 and later produces a number of
warnings, many of which are new with the recent compiler
versions.
This bug will be resolved in more than one patch to limit the
size of changesets. This is the second patch, fixing more
of the warnings.
crashes server!
The problem affects the scenario when index merge is followed by a filesort
and the sort buffer is not big enough for all the sort keys.
In this case the filesort function will read the data to the end through the
index merge quick access method (and thus closing the cursor etc),
but will leave the pointer to the quick select method in place.
It will then create a temporary file to hold the results of the filesort and
will add it as a sort output file (in sort.io_cache).
Note that filesort will copy the original 'sort' structure in an automatic
variable and restore it after it's done.
As a result at exiting filesort() we have a sort.io_cache filled in and
nothing else (as a result of close of the cursors at end of reading data
through index merge).
Now create_sort_index() will note that there is a select and will clean it up
(as it's been used already by filesort() reading the data in). While doing that
a special case in the index merge destructor will clean up the sort.io_cache,
assuming it's an output of the index merge method and is not needed anymore.
As a result the code that tries to read the data back from the filesort output
will get no data in both memory and disk and will crash.
Fixed similarly to how filesort() does it : by copying the sort.io_cache structure
to a local variable, removing the pointer to the io_cache (so that it's not freed
by QUICK_INDEX_MERGE_SELECT::~QUICK_INDEX_MERGE_SELECT) and restoring the original
structure (together with the valid pointer) after the cleanup is done.
This is a safe thing to do because all the structures are already cleaned up by
hitting the end of the index merge's read method (QUICK_INDEX_MERGE_SELECT::get_next())
and the cleanup code being written in a way that tolerates repeating cleanups.
mysql-test/r/index_merge.result:
Bug #44810: test case
mysql-test/t/index_merge.test:
Bug #44810: test case
sql/sql_select.cc:
Bug #44810: preserve the io_cache produced by filesort while cleaning up
the index merge quick access method (QUICK_INDEX_MERGE_SELECT).
