Zdenek Kotala wrote:
Heikki Linnakangas napsal(a):
I would suggest starting with putting some serious effort into
pg_migrator. This page layout conversion is actually pretty trivial
compared to all that, and even more so if you can get the page layout
conversion working in pg_migrator first.
By my opinion pg_migrator is good workaround but it is not suitable for
real production. For example TOAST relid protection is dirty hack and
you have problem with tablespaces and so on...
Sure, it's not perfect, that's exactly why I suggested working on it! If
you have something else that works better, that's fine, but you will
need to release it under the BSD license if you want help with it.
Which versions do you plan to support, initially?
Currently I'm able to upgrade from 8.1, 8.2 to 8.3, 8.4. It means
conversion between layout version 3 and 4. I'm verifying PLC now and
when this part will be ready it is very easy to implement others as well.
Hmm. I don't see any of that code in the directory you posted. ?
b) log_newpage is used for new page logging, but I use it for
storing converted page. It seems to me that it safe and
heap_xlog_newpage correctly works for new and converted page. I have
only doubt about assert macro mdextend/mdwrite which checks extend
vs.write.
That should be fine. In WAL replay, we don't distinguish between write
and extend.
But in this case the asserts macros in mdexted/mdwrite are odd and the
should be removed.
Those asserts are enforced during normal operation. It's just in WAL
replay that we extend the relation automatically when full pages are
restored. See XLogReadBuffer().
+ /* Hook for page layout convertor plugin */
+ typedef void (*plc_hook_type)(char *buffer);
+ extern PGDLLIMPORT plc_hook_type plc_hook;
That's not flexible enough. We've changed the internal representations
of data types in the past, and will likely do that in the future. The
hook therefore needs to have at least the tuple descriptor, to know
how to convert the tuples. I would suggest passing Relation, we have
that available at the call site, and that should contain all the
necessary information.
Good point, I thought about it. I currently don't use it but in the
future it could be useful. I will extend it.
Surely you need it already to do the packed varlen conversion?
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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