(Initial patch by Varun Gupta. Amended and added comments).
When the query has both
1. Aggregate functions that require sorting data by group, and
2. Window functions
we need to use two temporary tables. The first temp.table will hold the
join output. Then it is passed to filesort(). Reading it in sorted
order allows to compute the aggregate functions.
Then, we need to write their values into the second temp. table. Then,
Window Function computation step can pass that to filesort() and read
them in the order it needs.
Failure to create the second temp. table would cause an assertion
failure: window function could would not find where to get the values
of the aggregate functions.
Starting with commit baf276e6d4 (MDEV-19229)
the parameter innodb_undo_tablespaces can be increased from its
previous default value 0 while allowing an upgrade from old databases.
We will change the default setting to innodb_undo_tablespaces=3
so that the space occupied by possible bursts of undo log records
can be reclaimed after SET GLOBAL innodb_undo_log_truncate=ON.
We will not enable innodb_undo_log_truncate by default, because it
causes some observable performance degradation.
Special thanks to Thirunarayanan Balathandayuthapani for diagnosing
and fixing a number of bugs related to this new default setting.
Tested by: Matthias Leich, Axel Schwenke, Vladislav Vaintroub
(with both values of innodb_undo_log_truncate)
Before commit 6112853cda in MySQL 4.1.1
introduced the parameter innodb_file_per_table, all InnoDB data was
written to the InnoDB system tablespace (often named ibdata1).
A serious design problem is that once the system tablespace has grown to
some size, it cannot shrink even if the data inside it has been deleted.
There are also other design problems, such as the server hang MDEV-29930
that should only be possible when using innodb_file_per_table=0 and
innodb_undo_tablespaces=0 (storing both tables and undo logs in the
InnoDB system tablespace).
The parameter innodb_change_buffering was deprecated
in commit b5852ffbee.
Starting with commit baf276e6d4
(MDEV-19229) the number of innodb_undo_tablespaces can be increased,
so that the undo logs can be moved out of the system tablespace
of an existing installation.
If all these things (tables, undo logs, and the change buffer) are
removed from the InnoDB system tablespace, the only variable-size
data structure inside it is the InnoDB data dictionary.
DDL operations on .ibd files was optimized in
commit 86dc7b4d4c (MDEV-24626).
That should have removed any thinkable performance advantage of
using innodb_file_per_table=0.
Since there should be no benefit of setting innodb_file_per_table=0,
the parameter should be deprecated. Starting with MySQL 5.6 and
MariaDB Server 10.0, the default value is innodb_file_per_table=1.
mysql_discard_or_import_tablespace(): On successful
ALTER TABLE...DISCARD TABLESPACE, evict the table handle from the
table definition cache, so that ha_innobase::close() will be invoked,
like InnoDB expects to be the case. This will avoid an assertion failure
ut_a(table->get_ref_count() == 0) during IMPORT TABLESPACE.
ha_innobase::open(): Do not issue any ER_TABLESPACE_DISCARDED warning.
Member functions for DML will do that.
ha_innobase::truncate(), ha_innobase::check_if_supported_inplace_alter():
Issue ER_TABLESPACE_DISCARDED warnings, to compensate for the removal of
the warning in ha_innobase::open().
row_quiesce_write_indexes(): Only write information about committed
indexes. The ALTER TABLE t NOWAIT ADD INDEX(c) in the nondeterministic
test case will most of the time fail due to a metadata lock (MDL) timeout
and leave behind an uncommitted index.
Reviewed by: Sergei Golubchik
Some builders in our CI, most notably FreeBSD and IBM AIX, do not support
sparse files. Also, Microsoft Windows requires special means for creating
sparse files. Since these platforms do not run ./mtr --big-test, we will
for now simply move the test to a separate file that requires that option.
- Information_schema.innodb_tablespaces_encryption should print
undo tablespace name as innodb_undo001, innodb_undo002 and soon.
- Encryption test should include undo tablespaces count when
the tests are waiting for the condition to check whether all
tables are encrypted or decrypted.
recv_log_recover_10_4(): Widen the operand of bitwise and to 64 bits,
so that the upgrade check will work when the redo log record is located
more than 4 gigabytes from the start of the first file.
The log overwrite warnings are not being reliably emitted in all
debug-instrumented environments. It may be related to the
scheduling of some InnoDB internal activity, such as the purging
of committed transaction history.
