Jim Nasby wrote: > On 11/1/14, 8:41 AM, Petr Jelinek wrote: > >Well this is not BDR specific thing, the idea is that with logical > >replication, commit timestamp is not enough for conflict handling, you also > >need to have additional info in order to identify some types of conflicts > >conflicts (local update vs remote update for example). So the extradata > >field was meant as something that could be used to add the additional info > >to the xid. > > Related to this... is there any way to deal with 2 transactions that commit > in the same microsecond? It seems silly to try and handle that for every > commit since it should be quite rare, but perhaps we could store the LSN as > extradata if we detect a conflict?
Well, two things. One, LSN is 8 bytes and extradata (at least in this patch when I last saw it) is only 4 bytes. But secondly and more important is that detecting a conflict is done in node B *after* node A has recorded the transaction's commit time; there is no way to know at commit time that there is going to be a conflict caused by that transaction in the future. (If there was a way to tell, you could just as well not commit the transaction in the first place.) -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
