From
http://support.microsoft.com/?id=288631
Running the Compact and Repair Database utility within Microsoft Access can
also improve the performance of the database. This utility makes a copy of
the database file and, if it is fragmented, rearranges how the database file
is stored on disk. When completed, the compacted database has reclaimed
wasted space, and is usually smaller than the original. By compacting the
database frequently, optimal performance of the database application is
ensured, and page corruptions due to hardware problems, power failures or
surges, and so on are resolved.
If a primary key exists in the table, compacting restores table records into
their primary key order. This provides the equivalent of Non-maintained
Clustered Indexes, and makes the read-ahead capabilities of the Microsoft
Jet database engine much more efficient.
Compacting also updates the table statistics within the database that are
used as Jet optimizes queries. These statistics can become outdated as data
is added, manipulated, and deleted from the various tables. Query speed will
be enhanced significantly, because they are now working with data that has
been rewritten to the tables in contiguous pages. Scanning sequential pages
is much faster than scanning fragmented pages. Queries are forced to
recompile/optimize after each database compaction.
