Re: block-level incremental backup

On Mon, Sep 16, 2019 at 9:30 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > Isn't some operations where at the end we directly call heap_sync
> > without writing WAL will have a similar problem as well?
>
> Maybe. Can you give an example?

Looking through the code, I found two cases where we do this. One is
a bulk insert operation with wal_level = minimal, and the other is
CLUSTER or VACUUM FULL with wal_level = minimal. In both of these
cases we are generating new blocks whose LSNs will be 0/0. So, I think
we need a rule that if the server is asked to back up all blocks in a
file with LSNs > some threshold LSN, it must also include any blocks
whose LSN is 0/0. Those blocks are either uninitialized or are
populated without WAL logging, so they always need to be copied.

Outside of unlogged and temporary tables, I don't know of any case
where make a critical modification to an already-existing block
without bumping the LSN. I hope there is no such case.

--
Robert Haas
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