Re: Add parallelism and glibc dependent only options to reindexdb

Michael Paquier <michael(at)paquier(dot)xyz> writes:
> - 0003 begins to be the actual fancy thing with the addition of a
> --jobs option into reindexdb. The main issue here which should be
> discussed is that when it comes to reindex of tables, you basically
> are not going to have any conflicts between the objects manipulated.
> However if you wish to do a reindex on a set of indexes then things
> get more tricky as it is necessary to list items per-table so as
> multiple connections do not conflict with each other if attempting to
> work on multiple indexes of the same table. What this patch does is
> to select the set of indexes which need to be worked on (see the
> addition of cell in ParallelSlot), and then does a kind of
> pre-planning of each item into the connection slots so as each
> connection knows from the beginning which items it needs to process.
> This is quite different from vacuumdb where a new item is distributed
> only on a free connection from a unique list. I'd personally prefer
> if we keep the facility in parallel.c so as it is only
> execution-dependent and that we have no pre-planning. This would
> require keeping within reindexdb.c an array of lists, with one list
> corresponding to one connection instead which feels more natural.

Couldn't we make this enormously simpler and less bug-prone by just
dictating that --jobs applies only to reindex-table operations?

> - 0004 is the part where the concurrent additions really matter as
> this consists in applying an extra filter to the indexes selected so
> as only the glibc-sensitive indexes are chosen for the processing.

I think you'd be better off to define and document this as "reindex
only collation-sensitive indexes", without any particular reference
to a reason why somebody might want to do that.

regards, tom lane