On Tue, Jul 20, 2021 at 4:03 PM Mark Dilger
<mark.dilger@enterprisedb.com> wrote:
> I was only imagining having a callback for injecting manifests or recovery configurations. It is not necessary that
thisbe done in the current patch set, or perhaps ever.
A callback where?
I actually think the ideal scenario would be if the server always did
all the work and the client wasn't involved in editing the tarfile,
but it's not super-easy to get there from here. We could add an option
to tell the server whether to inject the manifest into the archive,
which probably wouldn't be too bad. For it to inject the recovery
configuration, we'd have to send that configuration to the server
somehow. I thought about using COPY BOTH mode instead of COPY OUT mode
to allow for stuff like that, but it seems pretty complicated, and I
wasn't really sure that we'd get consensus that it was better even if
I went to the trouble of coding it up.
If we don't do that and stick with the current system where it's
handled on the client side, then I agree that we want to separate the
tar-specific concerns from the injection-type concerns, which the
patch does by making those operations different kinds of bbstreamer
that know only a relatively limited amount about what each other are
doing. You get [server] => [tar parser] => [recovery injector] => [tar
archiver], where the [recovery injector] step nukes the archive file
headers for the files it adds or modifies, and the [tar archiver] step
fixes them up again. So the only thing that the [recovery injector]
piece needs to know is that if it makes any changes to a file, it
should send that file to the next step with a 0-length archive header,
and all the [tar archiver] piece needs to know is that already-valid
headers can be left alone and 0-length ones need to be regenerated.
There may be a better scheme; I don't think this is perfectly elegant.
I do think it's better than what we've got now.
--
Robert Haas
EDB: http://www.enterprisedb.com