On 7/2/07, Jan Wieck <JanWieck at yahoo.com> wrote:
> The stuff I am currently (very slowly) working on is that very problem.
> Any long running transaction causes that the minxid in the SYNC's is
> stuck at that very xid during the entire runtime of the LRT. The problem
> with that is that the log selection in the slon worker uses an index
> scan who's only index scankey candidates are the minxid of one and the
> maxxid of another snapshot. That is the range of rows returned by the
> scan itself. Since the minxid is stuck, it will select larger and larger
> groups of log tuples only to filter out most of them on a higher level
> in the query via xxid_le_snapshot().

How the LRT problem is avoided in PGQ:

http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/skytools/skytools/sql/pgq/functions/pgq.batch_event_sql.sql?rev=1.2&content-type=text/x-cvsweb-markup

Basic idea is that there are only few LRT's, so its reasonable
to pick up bottom half of range by event txid, one-by-one.

-- 
marko