spider_db_mbase_util::open_item_func() is a monster function.
It is difficult to maintain while it is expected that we need to
modify it when a new SQL function or a new func_type is added.
We split the function into two distinct functions: one handles the
case of str != NULL and the other handles the case of str == NULL.
This refactoring was done in a conservative way because we do not
have comprehensive tests on the function.
It also fixes MDEV-29447 and MDEV-31338 where field items that are
arguments of a func item may be used before created / initialised.
Note this commit is adapted from a patch by Nayuta for MDEV-26285.
Fixed wrong assignment in calculate_block_sizes() for MEM_ROOT
The effect was that that ROOT_FLAG_THREAD_SPECIFIC was cleared and
the memory allocated by memroot would be contributed the the system,
not to the thread.
This exposed a bug in how "show explain for ..." allocated data.
- The thread that did provide the explain allocated data in the
"show explain" threads mem_root, which is marked as THREAD_SPECIFIC.
- Fixed by allocating the explain data in a temporary explain_mem_root
which is not THREAD_SPECIFIC.
Other things:
- Added extra checks when using update_malloc_size()
- Do not call update_malloc_size() for memory not registered with
update_malloc_size(). This avoid some wrong 'memory not freed' reports.
- Added a checking of 'thd->killed' to ensure that
main.truncate_notembedded.test still works.
The test gcol.gcol_purge would reliably hang on 10.6 on a
Microsoft Windows builder without this adjustment.
A similar adjustment was applied in
commit 3e40f9a7f3bbe82d96c8acccbb017deebfa00647
to the tests innodb.dml_purge and innodb.instant_alter_purge.
