49d976feaa
A spider_conn may outlive its associated ha_spider (in the field queued_ping_spider) used for connecting to and pinging the data node (a call to spider_db_ping(), guarded by the boolean field queued_ping). In a call to ha_spider::close() (which is often preceded with the deletion of the ha_spider itself), many cleanups happen, including freeing the associated spider_share, which is used by the spider_conn in spider_db_ping. Therefore it is necessary to reset both the queued_ping_spider and queued_ping fields, so that any further spider interaction with the data node will not trigger the call using the ha_spider including its freed spider_share. Also out of caution added an assert and internal error in case a connection has not been established (the db_conn field of type MYSQL * is NULL), and attempt to connect is skipped because both queued_connect and queued_ping are false. Note that this unlikely (if not impossible) scenario would not be a regression caused by this change, as it strictly falls under the scenario of this bug.
Code status:
ci.appveyor.com
MariaDB: The innovative open source database
MariaDB was designed as a drop-in replacement of MySQL(R) with more features, new storage engines, fewer bugs, and better performance.
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https://mariadb.com/kb/en/mariadb-vs-mysql-features/
https://mariadb.com/kb/en/mariadb-versus-mysql-compatibility/
https://mariadb.com/kb/en/new-and-old-releases/
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