Pavan Deolasee wrote:
In a typical scenario, user might create a table and load data in the
table as part of a single transaction (e.g pg_restore). In this case,
it would help if we create the tuples in the *frozen* state to avoid
any wrap-around related issues with the table. Without this, very
large read-only tables would require one round of complete freezing
if there are lot of transactional activities in the other parts of
the database. And when that happens, it would generate lots of
unnecessary IOs on these large tables.
If that works, then we might also want to set the visibility hint bits.
Not because lookup of that information is expensive - the tuples all
came from the same transaction, virtually guaranteeing that the relevent
pg_clog page stays in memory after the first few pages.
But by setting them immediatly we'd save some IO, since we won't dirty
all pages during the first scan.
I don't know if this is a real problem for anybody, but I could think
of its use case, at least in theory.
A cannot speak for freeze-on-restore, but in a project I'm currently
working on, the IO caused (I guess) by hint-bit updates during the
first scan of the table is at least noticeably...
regards, Florian Pflug
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