Re: help with version checking

[Karsten Hilbert <Karsten(dot)Hilbert(at)gmx(dot)net>]

In GNUmed we have created a function

	gm_concat_table_structure()

in

	http://cvs.savannah.gnu.org/viewcvs/gnumed/gnumed/server/sql/gmSchemaRevisionViews.sql?rev=1.6&root=gnumed&view=log

which returns a reproducable, human-readable TEXT
concatenation of all the relevant parts of the schema.

We then do

	select md5(gm_concat_table_structure());

and compare the output to known hashes for certain schema
versions. That way we don't simply "believe" what is in a
table "current_version" but rather actually *detect* (within
reasonable limits) the version.

It works well so far, no noticably delay even during client
startup (which does the check and complains on mismatches).
It may not scale particularly well to very large schemata,
possibly.

Karsten
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