From: | rakeshkumar464 <rakeshkumar464(at)outlook(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Incremental / Level -1 backup in PG |
Date: | 2017-03-22 18:11:06 |
Message-ID: | 1490206266771-5951343.post@n3.nabble.com |
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Thread: | |
Lists: | pgsql-general |
>note postgres' WAL archive is by block, not by transaction.
My understanding is that only the first time a block is updated after a
checkpoint,
is the entire block is written to the WAL logs. And for that
full_page_writes has to be set to ON.
The only other time PG writes entire block to the WAL is during the time of
backup regardless of full_page_writes setting.
AFAIK rest of the time, WAL takes only row changes. Otherwise PG will be
generating large number
of WAL logs.
I hope I am right :-)
> also note that postgres effectively does copy-on-write, since update's are
> treated
>as insert+delete, so the same blocks aren't written over and over nearly
>as much as they might be in the oracle storage model.
Good point.
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