Hi nanyi607rao, sorry for the delayed response, in part due to the Easter holidays.
"nanyi607rao"
If character_set in different Query_log_events changed, worker threads may apply them with wrong character_set. the codes leading this problem is in Query_log_event::do_apply_event, that is: if (charset_inited) { if (rli->cached_charset_compare(charset)) { /* Verify that we support the charsets found in the event. */ if (!(thd->variables.character_set_client= get_charset(uint2korr(charset), MYF(MY_WME))) || !(thd->variables.collation_connection= get_charset(uint2korr(charset+2), MYF(MY_WME))) || !(thd->variables.collation_server= get_charset(uint2korr(charset+4), MYF(MY_WME)))) {
There is a charset[6] in rli, which cached last Query_log_event's charset in serial replication. But in parallel replication it would lead mistake, because every worker thread can read and set rli->charset[6], so rli->charset[6] isn't any worker threads' last Query_log_event charset. but rli->charset[6] can affect every worker threads' thd->variables.character_set_* setting.
Right, I see. Probably the cached_charset just needs to be moved into the rpl_group_info struct. I have filed a bug for this that I will fix: https://mariadb.atlassian.net/browse/MDEV-6156 Thanks a lot for finding this, as usual your input on parallel replication is most useful, keep it coming! - Kristian.