Monty Taylor wrote:
I think Stewart's question was - now that we've gotten rid of a central
system database, if we were to store data about tablespaces, where would
we keep it?
...and my answer to that was not exactly clear...
For my part, I'm not totally sure I agree that it is important the users
can manage tablespaces through Drizzle commands.
Fair enough. The management will also partially be engine-specific, so
having Drizzle commands may not be of great value. I've also seen other
systems wrapping commands from underlying systems (trying to "help" the
users) so that they become too complex for their own good.
I mean, I hear what you're saying, and if you accept the premise that
Tablespaces are good and/or required, then managing them through Drizzle
commands is sensible - but I'm always extremely wary of systems that try
to re-write all of UNIX. Again. My question is, other than complexity of
database config and setup and a possible bootstrapping problem, what is
it that tablespaces gain us?
We've already got filesystems. We've got LVM. If we're on Solaris or OSX
I've got the much-lauded (yet still uselessly licensed) ZFS. OR, if
we've wasted^?^?^?^?^? spent money on a big-ass SAN, I've got the
storage management features in the SAN. What do I gain by having the
database engine manage this itself as well?
I think it is severely limiting that you must specify to an engine that
the data it manages has to be below a certain directory, just because
the database was created with a storage specification encapsulating that
directory. Regardless of the advanced state of file systems, I think it
is very important that you provide future extensibility for a database,
and I think that is best provided by having tablespaces.
Having advanced features in the SAN is fine. However, for some features
it can be useful to manage them from the database level because it helps
maintain consistency and it relieves the user the burden of having to
provide two different commands for any reconfiguration.
(I'm both trolling and honestly asking here...)
Roy Lyseng wrote:
Stewart,
this is a good question. Some comments below to start off a discussion...
Different engines have very different requirements for management of
tablespaces, so I think it is important that tablespaces are managed
entirely by the engine on the micro-level. Yet, on a higher level, it is
important that users can manage tablespaces through Drizzle commands
that generalize the management as much as possible.
How is this achievable?
- Create, modify and drop tablespace commands supported by Drizzle.
- Engine-specific parameters to tablespace commands
- Engine-specific namespace of tablespaces simplifies management.
- Tablespace configuration data can be managed by the engine or by the
server, interfaces for both can be provided.
- In the simplest case, the server stores all config data (XML, blob?)
and provides them to the engine when the server initiates the engine.
In the case of a distributed engine, it is much easier to keep
tablespace information consistent by managing config data in the engine,
in particular when multiple servers attach to the same engine.
BTW, HADB (a distributed server/engine) does not have tablespaces (or
rather it has a single unnamed tablespace). However, each server node is
given a list of file names on startup, and the concatenated storage
space provided by these files is used as storage space for that node.
Information about schemas and tables and mapping to which nodes they are
stored in is entirely through system-managed tables (the data dictionary).
Thanks,
Roy
Stewart Smith wrote:
On Mon, Oct 20, 2008 at 10:06:59AM +0200, Roy Lyseng wrote:
IMHO, forcing the database(schema)/directory relationship is the
bigger problem. With tablespaces there would be no need for symlinks.
You also have to think about where this information is being stored. How
will drizzle know where to look for tablespaces?
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