02-27-2013
There most likely is a way to find out what is in the first 100 mb of the file, but that is not how databases work. One reason database systems were invented is that you do not have to bother with this kind of things, so the documentation for this is hard to find and understand.
I could tell you how to do this for Oracle systems if I'd know the exact version, but there would be a LOT research you'd have to do and I'm not sure if recreating the database wouldn't be less straining on your resources.
A quick google search revealed that shrinking mysql datafiles is not a built in feature for that database system, but there are tools that can do it. The native approach would be to add a datafile of the desired size, move all data there and drop the old ones (and I guess that is what those tools do).
Edit: Using tools like vi or awk on database files usually is a bad idea and will most likely corrupt your database.
Last edited by cero; 02-27-2013 at 04:30 AM..
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LEARN ABOUT DEBIAN
mysql-schema-diff
MYSQLDIFF(1p) User Contributed Perl Documentation MYSQLDIFF(1p)
NAME
mysql-schema-diff - compare MySQL database schemas
SYNOPSIS
mysql-schema-diff [B<options>] B<database1> B<database2>
mysql-schema-diff --help
DESCRIPTION
mysql-schema-diff is a Perl script front-end to the CPAN <http://www.perl.com/CPAN> module MySQL::Diff
<http://search.cpan.org/search?module=MySQL::Diff> which compares the data structures (i.e. schema / table definitions) of two MySQL
<http://www.mysql.com/> databases, and returns the differences as a sequence of MySQL commands suitable for piping into mysql which will
transform the structure of the first database to be identical to that of the second (c.f. diff and patch).
Database structures can be compared whether they are files containing table definitions or existing databases, local or remote.
N.B. The program makes no attempt to compare any of the data which may be stored in the databases. It is purely for comparing the table
definitions. I have no plans to implement data comparison; it is a complex problem and I have no need of such functionality anyway.
However there is another program coldiff <http://rossbeyer.net/software/mysql_coldiff/> which does this, and is based on an older program
called datadiff which seems to have vanished off the 'net.
For PostgreSQL there are similar tools such as pgdiff <http://pgdiff.sourceforge.net/> and apgdiff <http://apgdiff.startnet.biz/>.
EXAMPLES
# compare table definitions in two files
mysql-schema-diff db1.mysql db2.mysql
# compare table definitions in a file 'db1.mysql' with a database 'db2'
mysql-schema-diff db1.mysql db2
# interactively upgrade schema of database 'db1' to be like the
# schema described in the file 'db2.mysql'
mysql-schema-diff -A db1 db2.mysql
# compare table definitions in two databases on a remote machine
mysql-schema-diff --host=remote.host.com --user=myaccount db1 db2
# compare table definitions in a local database 'foo' with a
# database 'bar' on a remote machine, when a file foo already
# exists in the current directory
mysql-schema-diff --host2=remote.host.com --password=secret db:foo bar
OPTIONS
More details to come; for now run "mysql-schema-diff --help".
INTERNALS
For both of the database structures being compared, the following happens:
o If the argument is a valid filename, the file is used to create a temporary database which "mysqldump -d" is run on to obtain the table
definitions in canonicalised form. The temporary database is then dropped. (The temporary database is named
"test_mysqldiff_temp_something" because default MySQL permissions allow anyone to create databases beginning with the prefix "test_".)
o If the argument is a database, "mysqldump -d" is run directly on it.
o Where authentication is required, the hostname, username, and password given by the corresponding options are used (type
"mysql-schema-diff --help" for more information).
o Each set of table definitions is now parsed into tables, and fields and index keys within those tables; these are compared, and the
differences outputted in the form of MySQL statements.
BUGS, DEVELOPMENT, CONTRIBUTING
See <http://software.adamspiers.org/wiki/mysqldiff>.
COPYRIGHT AND LICENSE
Copyright (c) 2000-2011 Adam Spiers. All rights reserved. This program is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.
SEE ALSO
MySQL::Diff, MySQL::Diff::Database, MySQL::Diff::Table, MySQL::Diff::Utils, mysql, mysqldump, mysqlshow
AUTHOR
Adam Spiers <mysqldiff@adamspiers.org>
perl v5.14.2 2012-04-06 MYSQLDIFF(1p)