Joshua D. Drake wrote:
On Fri, 2009-11-20 at 11:14 +0900, Josh Berkus wrote:
On 11/15/09 11:07 PM, Heikki Linnakangas wrote:
- When replaying b-tree deletions, we currently wait out/cancel all
running (read-only) transactions. We take the ultra-conservative stance
because we don't know how recent the tuples being deleted are. If we
could store a better estimate for latestRemovedXid in the WAL record, we
could make that less conservative.
Simon was explaining this issue here at JPUGCon; now that I understand
it, this specific issue seems like the worst usability issue in HS now.
Bad enough to kill its usefulness for users, or even our ability to get
useful testing data; in an OLTP production database with several hundred
inserts per second it would result in pretty much never being able to
get any query which takes longer than a few seconds to complete on the
slave.
I am pretty sure that OmniTI, PgExperts, EDB and CMD all have customers
that are doing more than that... This sounds pretty significant.
Right. The major use I was hoping for from HS was exactly to be able to
run long-running queries. In once case I am thinking of we have moved
the business intelligence uses off the OLTP server onto a londiste
replica, and I was really wanting to move that to a Hot Standby server.
cheers
andrew
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