Remove one of the major sources of race condiitons in mariadb-test.
Normally, mariadb_close() sends COM_QUIT to the server and immediately
disconnects. In mariadb-test it means the test can switch to another
connection and sends queries to the server before the server even
started parsing the COM_QUIT packet and these queries can see the
connection as fully active, as it didn't reach dispatch_command yet.
This is a major source of instability in tests and many - but not all,
still less than a half - tests employ workarounds. The correct one
is a pair count_sessions.inc/wait_until_count_sessions.inc.
Also very popular was wait_until_disconnected.inc, which was completely
useless, because it verifies that the connection is closed, and after
disconnect it always is, it didn't verify whether the server processed
COM_QUIT. Sadly the placebo was as widely used as the real thing.
Let's fix this by making mariadb-test `disconnect` command _to wait_ for
the server to confirm. This makes almost all workarounds redundant.
In some cases count_sessions.inc/wait_until_count_sessions.inc is still
needed, though, as only `disconnect` command is changed:
* after external tools, like `exec $MYSQL`
* after failed `connect` command
* replication, after `STOP SLAVE`
* Federated/CONNECT/SPIDER/etc after `DROP TABLE`
and also in some XA tests, because an XA transaction is dissociated from
the THD very late, after the server has closed the client connection.
Collateral cleanups: fix comments, remove some redundant statements:
* DROP IF EXISTS if nothing is known to exist
* DROP table/view before DROP DATABASE
* REVOKE privileges before DROP USER
etc
Problem:
=======
- In case of large file size, InnoDB eagerly adds the new extent
even though there are many existing unused pages of the segment.
Reason is that in case of larger file size, threshold
(1/8 of reserved pages) for adding new extent has been
reached frequently.
Solution:
=========
- Try to utilise the unused pages in the segment before adding
the new extent in the file segment.
need_for_new_extent(): In case of larger file size, try to use
the 4 * FSP_EXTENT_SIZE as threshold to allocate the new extent.
fseg_alloc_free_page_low(): Rewrote the function to allocate
the page in the following order.
1) Try to get the page from existing segment extent.
2) Check whether the segment needs new extent
(need_for_new_extent()) and allocate the new extent,
find the page.
3) Take individual page from the unused page from
segment or tablespace.
4) Allocate a new extent and take first page from it.
Removed FSEG_FILLFACTOR, FSEG_FRAG_LIMIT variable.
WL#6326 in MariaDB 10.2.2 introduced a potential hang on purge or rollback
when an index tree is being shrunk by multiple levels.
This fix is based on
mysql/mysql-server@f2c5852630
with the main difference that our version of the test case uses
DEBUG_SYNC instrumentation on ROLLBACK, not on purge.
btr_cur_will_modify_tree(): Simplify the check further.
This is the actual bug fix.
row_undo_mod_remove_clust_low(), row_undo_mod_clust(): Add DEBUG_SYNC
instrumentation for the test case.
