BUG#39325 Server crash inside MYSQL_LOG::purge_first_log halts replicaiton
The patch reverses the order of the purging and updating events for log and relay-log.info/index files respectively.
This solves the problem of having holes caused by crashes happening between updating info/index files and purging logs.
NOTE: This is a combined patch for BUG#38826 and BUG#39325. This patch is based on bugteam tree and takes into account reviewers suggestions.
Bug #18453 Warning/error message if there is a mismatch between ...
There were three problems:
1. the reported lack of warnings for the BEFORE syntax of PURGE;
2. the similar lack of warnings for the TO syntax;
3. incompatible behaviour between the two in that the latter blanked out
regardlessly of presence or lack the actual file corresponding to
an index record; the former version gave up at the first mismatch.
fixed with deploying the warning's generation and synronizing logics of
purge_logs() and purge_logs_before_date().
my_stat() is called in either of two branches of purge_logs() (responsible
for the TO syntax of PURGE) similarly to how it has behaved in the BEFORE syntax.
If there is no actual binlog file, my_stat returns NULL and my_delete is
not invoked.
A critical error is reported to the user if a file from the index
could not be retrieved info about or deleted with a system error code
different than ENOENT.
