MDEV-21512 InnoDB may hang due to SPATIAL INDEX
MySQL 5.7.29 includes the following fix: Bug #30287668 INNODB: A LONG SEMAPHORE WAIT mysql/mysql-server@5cdbb22b51cf2b35dbdf5666a251ffbec2f84dec There is no test case. It seems that the problem could occur when a spatial index is large and peculiar enough so that multiple R-tree leaf pages will have the exactly same maximum bounding rectangle (MBR). The commit message suggests that the hang can occur when R-tree non-leaf pages are being merged, which should only be possible during transaction rollback or the purge of transaction history, when the R-tree index is at least 2 levels high and very many records are being deleted. The message says that a comparison result that two spatial index node pointer records are equal will cause an infinite loop in rtr_page_copy_rec_list_end_no_locks(). Hence, we must include the child page number in the comparison to be consistent with mysql/mysql-server@2e11fe0e152e34d73579e1a9ec19aedc3f6010f6. We fix this bug in a simpler way, involving fewer code changes. cmp_rec_rec(): Renamed from cmp_rec_rec_with_match(). Assert that rec2 always resides in an index page. Treat non-leaf spatial index pages specially.
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