Re: Shared PostgreSQL libraries and symbol versioning

Greetings,

* Peter Eisentraut (peter(dot)eisentraut(at)2ndquadrant(dot)com) wrote:
> On 4/5/18 02:04, Pavel Raiskup wrote:
> > Hello, for the support of multiple versions of PostgreSQL RPM packages on
> > one system, we are thinking about having only one libpq.so.5
> > (libecpg.so.6, libpgtype.so.3 respectively) supported and about building
> > (linking) all the PostgreSQL package versions against that. The pattern
> > would mean that we'd have to update the system-wide libraries before
> > adding support for new PostgreSQL major version and that the older
> > packages (say version =< 9.6) would be run against libs from newer PG
> > package (say libpq.so.5 from v10).
> >
> > Do you think it is a good idea in general?
>
> yes

Adding symbol versioning would probably be a good idea, yes, though we
don't have as much need as others since we've really had a rather stable
ABI for a long time.

> > As a followup thought; there are probably two major obstacles ATM
> >
> > - the DSOs' symbols are not yet versioned, and
> > - the build-system doesn't seem to know how to -lpq link against
> > external libpq.so

I've not looked but neither of those strike me as terribly difficult to
overcome, assuming they need to be overcome.

> It's not clear to me why you would need these, given that Debian has
> been doing this for many years without this.

Huh?

objdump -T /usr/lib/x86_64-linux-gnu/libpq.so.5.10

...
0000000000021a50 g DF .text 000000000000014c Base pg_char_to_encoding
00000000000270d0 g DF .text 000000000000002c Base PQsslStruct
0000000000013880 g DF .text 00000000000001d2 Base PQmakeEmptyPGresult
0000000000017900 g DF .text 0000000000000012 Base PQmblen
000000000000ac20 g DF .text 00000000000002c0 Base PQencryptPasswordConn
000000000000fcc0 g DF .text 00000000000000f3 Base PQresetPoll
0000000000014790 g DF .text 00000000000000ef Base PQsendQuery
000000000001fc50 g DF .text 0000000000000061 Base initPQExpBuffer
00000000000152a0 g DF .text 0000000000000012 Base PQsendDescribePortal
...

No, Debian doesn't do symbol versioning for libpq and I don't believe it
ever has.

There are other libraries in Debian where the are using symbol
versioning, of course, but libpq isn't one of those.

Thanks!

Stephen