It's now possible to use pgloader to migrate from PostgreSQL to PostgreSQL.
That might be useful for several reasons, including applying user defined
cast rules at COPY time, or just moving from an hosted solution to another.
In order to later be able to have more worker threads sharing the
load (multiple readers and/or writers, maybe more specialized threads
too), have all the stats be managed centrally by a single thread. We
already have a "monitor" thread that get passed log messages so that the
output buffer is not subject to race conditions, extend its use to also
deal with statistics messages.
In the current code, we send a message each time we read a row. In some
future commits we should probably reduce the messaging here to something
like one message per batch in the common case.
Also, as a nice side effect of the code simplification and refactoring
this fixes#283 wherein the before/after sections of individual CSV
files within an ARCHIVE command where not counted in the reporting.
It's now possible to use several files in a BEFORE LOAD EXECUTE section,
and to mix DO and EXECUTE parts, bringing lots of flexibility in the
commands. Also it actually simplifies the parser.
That allows using the same SQL files as usual when using pgloader, as it
even supports the \i and \ir psql features (and dollar quoting, etc).
In passing, refactor docs to avoid saying the same things all over the
place, which isn't a very good idea in a man page, at least as far
editing it is involved.
