Hi Robert,
On Mar 25, 2010, at 4:32 PM, Robert Hodges wrote:
Thanks for the quick explanation of replication. I am starting to
recommend
that our customers look at PBXT as a possible substitute for InnoDB;
this
seems like one more reason.
For Jay and my upcoming talk we will definitely discuss physical
replication
approaches. We may need to run some information past you to ensure
we give
PBXT accurate credit.
That would be great. Please don't hesitate to ask.
Cheers, Robert
On 3/24/10 1:11 AM PDT, "Paul McCullagh"
<[email protected]>
wrote:
This is a very interesting point. Physical and logical replication
are kind
of like Yin and Yang for building systems.
I was thinking of pointing out in the talk the work going on in
PostgreSQL
with PG 9 and streaming replication/hot standby. The PostgreSQL
approach,
as you are probably aware, has been to implement very solid physical
replication while leaving logical replication to external, trigger-
based
products like Londiste.
This is basically the PBXT approach.
How do you get around some of the issues like snapshot maintenance
for
queries that are currently consuming cycles in the PostgreSQL
effort? In
the current PG 9 alpha users may have to choose between between up
to date
slaves and ability to run queries that maintain a snapshot for a
lengthy
period of time.
Should not be much of a problem because PBXT MVCC implementation can
handle long running snapshot queries/transactions. PBXT stores all
versions of a row on disk, so it does not limit the size of a
snapshot.
However, each version of a row is indexed. So a long running snapshot
can lead to inflation of the index. This is not a problem for
updates,
however. Especially not replicated updates which are based on the
internal row ID. So a snapshot should not have that much affect on
the
speed at which replication changes are applied.
But, it can affect the speed of long running SELECTs that are being
done on the slave.
Best regards,
Paul
--
Paul McCullagh
PrimeBase Technologies
www.primebase.org
www.blobstreaming.org
pbxt.blogspot.com
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