Implement a generic-function API to discover the source database schema and
populate pgloader internal version of the catalogs. Cut down three copies of about
the same code-path down to a single shared one, thanks to applying some amount
of OOP to the code.
The latter is not tested yet, but should have no impact if not used. Given
how rare it is that I get a chance to play around with a MS SQL instance
anyway, it might be better to push blind changes for it when it doesn't
impact existing features…
In a previous commit we re-used the package name pgloader.copy for the now
separated implementation of the COPY protocol, but this package was already
in use for the implementation of the COPY file format as a pgloader source.
Oops.
And CCL was happily doing its magic anyway, so that I've been blind to the
problem.
To fix, rename the new package pgloader.pgcopy, and to avoid having to deal
with other problems of the same kind in the future, rename every source
package pgloader.source.<format>, so that we now have pgloader.source.copy
and pgloader.pgcopy, two visibily different packages to deal with.
This light refactoring came with a challenge tho. The split in between the
pgloader.sources API and the rest of the code involved some circular
depencendies in the namespaces. CL is pretty flexible here because it can
reload code definitions at runtime, but it was still a mess. To untangle it,
implement a new namespace, the pgloader.load package, where we can use the
pgloader.sources API and the pgloader.connection and pgloader.pgsql APIs
too.
A little problem gave birth to quite a massive patch. As it happens when
refactoring and cleaning-up the dirt in any large enough project, right?
See #748.
Having been given a test instance of a MS SQL database allows to quickly
fix a series of assorted bugs related to schema handling of MS SQL
databases. As it's the only source with a proper notion of schema that
pgloader supports currently, it's not a surprise we had them.
Fix#343. Fix#349. Fix#354.
It should return the fetched catalog rather than the count of objects,
which is only used for statistics purposes. Fix#349.
This problem once again shows that we lack proper testing environment
for MS SQL source :/
In order to share more code in between the different source types,
finally have a go at the quite horrible mess of anonymous data
structures floating around.
Having a catalog and schema instances not only allows for code cleanup,
but will also allow to implement some bug fixes and wishlist items such
as mapping tables from a schema to another one.
Also, supporting database sources having a notion of "schema" (in
between "catalog" and "table") should get easier, including getting
on-par with MySQL in the MS SQL support (materialized views has been
asked for already).
See #320, #316, #224 for references and a notion of progress being made.
In passing, also clean up the copy-databases methods for database source
types, so that they all use a fetch-metadata generic function and a
prepare-pgsql-database and a complete-pgsql-database generic function.
Actually, a single method does the job here.
The responsibility of introspecting the source to populate the internal
catalog/schema representation is now held by the fetch-metadata generic
function, which in turn will call the specialized versions of
list-all-columns and friends implementations. Once the catalog has been
fetched, an explicit CAST call is then needed before we can continue.
Finally, the fields/columns/transforms slots in the copy objects are
still being used by the operative code, so the internal catalog
representation is only used up to starting the data copy step, where the
copy class instances are then all that's used.
This might be refactored again in a follow-up patch.
The newly added statistics are showing that read+write times are not
enough to explain how long we wait for the data copying, so it must be
the workers setup rather than the workers themselves.
From there, let lparallel work its magic in scheduling the work we do in
parallel in pgloader: rather than doing blocking receive-result calls
for each table, only receive-result at the end of the whole
copy-database processing.
On test data here on the laptop we go from 6s to 3s to migrate the
sakila database from MySQL to PostgreSQL: that's because we have lots of
very small tables, so the cost of waiting after each COPY added up quite
quickly.
In passing, stop sharing the same connection object in between parallel
workers that used to be controlled active in-sequence, see the new API
clone-connection (which takes over new-pgsql-connection).
When devising the common API, the first step has been to implement
specific methods for each generic function of the protocol. It now
appears that in some cases we don't need the extra level of flexibility:
each change of the API has been systematically reported to all the
specific methods, so just use a single generic definition where possible.
In particular, introduce new intermediate class for COPY subclasses
allowing to share more common code in the methods implementation, rather
than having to copy/paste and maintain several versions of the same
code.
It would be good to be able to centralize more code for the database
sources and how they are organized around metadata/import-data/complete
schema, but it doesn't look obvious how to do it just now.
Update the stats used to be a quite simple incf and doing it once per
read row was good enough, but now that it involves sending a message to
the monitor thread let's only send a message per batch, reducing the
communication load here.
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.
As seen in #287 the previous decision to force quoting to :none is
wrong, because index names in MS SQL source database might contain
spaces, and then need to be quoted.
Let's see what happens if we do it the usual way for MS SQL too, and
allow users to control the quoting behaviour of pgloader here.
This option is dangerous and allows to skip ALL triggers when loading
data against PostgreSQL. This includes foreign key constraints
definitions and will allow loading data out of order.
When using both the options "create no table" and "disable triggers" it
will be possible to load data into a schema prepared by your favorite
external tool, at the cost of not validating FK constraints. Use with
care.
Fix#167.
That's the big refactoring patch I've been sitting on for too long.
First, refactor connection handling to use a uniformed "connection"
concept (class and generic functions API) everywhere, so that the COPY
derived objects just use that in their :source-db and :target-db slots.
Given that, we don't need no messing around with *pgconn* and *myconn-*
and other special variables at all anywhere in the tree.
Second, clean up some oddities accumulated over time, where some parts
of the code didn't get the memo when new API got into place.
Third, fix any other oddity or missing part found while doing those
first two activities, it was long overdue anyway...
