Re: libpq compression (part 3)

On Tue, May 14, 2024 at 3:22 PM Jacob Burroughs
<jburroughs(at)instructure(dot)com> wrote:
> What if we went with:
> Server side:
> * `libpq_compression=on` (I just want everything the server supports
> available; probably the most common case)
> * `libpq_compression=off` (I don't want any compression ever with this server)
> * `libpq_compression=lzma;gzip` (I only want these algorithms for
> whatever reason)
> * `libpq_compression=lzma:client_to_server=off;gzip:server_to_client=off`
> (I only want to send data with lzma and receive data with gzip)
> Client side:
> *`compression=on` (I just want compression; pick sane defaults
> automatically for me; probably the most common case)
> * `compression=off` (I don't want any compression)
> * `compression=lzma;gzip` (I only want these algorithms for whatever reason)
> * `compression=lzma:client_to_server=off;gzip:server_to_client=off` (I
> only want to receive data with lzma and send data with gzip)
>
> `client_to_server`/`server_to_client` is a bit verbose, but it's very
> explicit in what it means, so you don't need to reason about who is
> sending/receiving/etc in a given context, and a given config string
> applied to the server or the client side has the same effect on the
> connection.

IMHO, that's a HUGE improvement. But:

* I would probably change is the name "libpq_compression", because
even though we have src/backend/libpq, we typically use libpq to refer
to the client library, not the server's implementation of the wire
protocol. I think we could call it connection_encryption or
wire_protocol_encryption or something like that, but I'm not a huge
fan of libpq_compression.

* I would use commas, not semicolons, to separate items in a list,
i.e. lzma,gzip not lzma;gzip. I think that convention is nearly
universal in PostgreSQL, but feel free to point out counterexamples if
you were modelling this on something.

* libpq_compression=lzma:client_to_server=off;gzip:server_to_client=off
reads strangely to me. How about making it so that the syntax is like
this:

libpq_compression=DEFAULT_VALUE_FOR_BOTH_DIRECTIONS:client_to_server=OVERRIDE_FOR_THIS_DIRECTION:servert_to_client=OVERRIDE_FOR_THIS_DIRECTION

With all components being optional. So this example could be written
in any of these ways:

libpq_compression=lzma;server_to_client=gzip
libpq_compression=gzip;client_to_server=lzma
libpq_compression=server_to_client=gzip;client_to_server=lzma
libpq_compression=client_to_server=lzma;client_to_server=gzip

And if I wrote libpq_compression=server_to_client=gzip that would mean
send data to the client using gzip and in the other direction use
whatever the default is.

--
Robert Haas
EDB: http://www.enterprisedb.com