Aleksander Alekseev <aleksan...@timescale.com> writes: > Hi, > > Previously it was pointed out [1] that manipulating the pg_control > file from Cluster.pm may be beneficial under certain conditions. [...] > Unfortunately this can't be done at the moment. One of the reasons is > that the ControlFileData structure stores platform-dependent types > like `int`. The size of the structure and all the offsets within it > are variable. The second reason is that integer representation may be > little- or big-endian depending on the platform. The third reason is > that the alignment of the fields may differ even if we switch to types > of the known size like int32 / int64.
Notwitstanding Tom's objections, these are not reasons for not being able to manipulate these values from Perl. The `i` and `I` formats for pack/unpack (see https://perldoc.perl.org/functions/pack) use what the C compiler calls `int`, in terms of both endianness and size. > For named reasons, manipulating pg_upgrade from Perl is impractical, > considering the number of environments we support. > > I see two possible solutions: > > 1) Provide a tool written in C that allows changing pg_control, e.g. > `pg_writecontoldata` or maybe a flat like `pg_controldata -w`. The > tool can be executed from Perl, so it shouldn't know about > sizeof(int), alignment and endiness. 1.5) Use Perl's pack/unpack functions, which are explicitly desgined for exactly this use case. - ilmari
