MDEV-27233-22979-30370 Add and update tests for spider init bugs
For development only - will squash this into another commit later - do
not push.
mdev_27233_v2: a variant of mdev-27233 where the spider plugin is
loaded in during server startup.
mdev_30370: we update this test to use mysqld_cmd instead of the
noisy mysqld_bootstrap_cmd. We have to kill the server first to avoid
"Can't lock aria control file"
With the change in commit c160a115b8b that was pushed to fix
mdev-27233 but later reverted because of mdev-29904, mdev_27233 and
the updated mdev_30370 would pass, but not mdev_27233_v2 ("[ERROR]
SPIDER plugin initialization failed at 'drop procedure if exists
mysql.spider_fix_one_table' by 'Unknown storage engine 'Aria''") or
mdev_30370 if it uses mysqld_bootstrap_cmd (post-test check will fail
when running this case with some other case, e.g. mtr mdev_30370
mdev_29562).
MDEV-27095 spider should be installed with INSTALL SONAME ha_spider
There are several plugins in ha_spider: spider, spider_alloc_mem,
spider_wrapper_protocols, spider_rewrite etc.
INSTALL PLUGIN foo SONAME ha_spider causes all the other ones to be
installed by the init queries where foo is any of the plugins.
This introduces unnecessary complexiy. For example it reads
mysql.plugins to find all other plugins, causing the hack of moving
spider plugin init to a separate thread.
To install all spider related plugins, install soname ha_spider should
be used instead.
MDEV-29676 refactored and documented spider_get_share() and friends
Extracted out common subroutines, gave more meaningful names etc,
added comments etc.
Also:
- Documented active servers load balancing reads, and other fields in
SPIDER_SHARE etc.
- Removed commented out code
- Documented and refactored self-reference check
- Removed some unnecessary functions
- Renamed unhelpful root_count
- Refactored spider_get_{sts,crd}, where we turn get_type into an enum
- Cleaned up spider_mbase_handler::show_table_status() and
spider_mbase_handler::show_index()
