On Nov 13, 2009, at 3:46 AM, Ozgun Erdogan wrote:
> How strong is the coupling between XLOG entries and database pages?
> That is, assume that I am inserting one row to a database table. Is
> there anyway for me to construct the related XLOG entry before calling
> the heap insert function? Or, are XLOG files conceptually binary diffs
> for database pages, moving forward in time?
The latter. The converse of your question is much more common, "How
can I reconstruct the statements that changed my database from the
xlog contents", with the same answer.
> Another question that I had relates to XLOG files and tables. If I
> have two databases and one is set up as a slave to the other, is it
> possible for the slave to have fewer tables than the master? If it is
> possible, is that because tables don't share pages?
That depends on how you implement replication. Since you ask in the
context of xlogs I'll assume you mean a warm standby slave via WAL
shipping and there the answer is no. Well, you might be able to work
something out by using record-based log shipping but even if that
could work it would take a lot of, well, work.
> Again I'm new to Postgres, and am curious about how stuff works
> underneath the covers. I figured asking this list would be the
> simplest way to figure things out.
Yep :)
Erik Jones, Database Administrator
Engine Yard
Support, Scalability, Reliability
866.518.9273 x 260
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