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<concept xml:lang="en" id="GUID-1824B323-AAA8-5403-A4CF-D1F530CBDAF5"><title>Introduction to space reclamation and compaction</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>When a stream is replaced or deleted, the space it occupies is not immediately available for re-use by other streams. There are two things you can do about this:</p> <ul><li id="GUID-4DDE58C7-78C8-5356-A7EA-FA1D24BFE327"><p>reclaim unused space; this makes it available for re-use by the store</p> </li> <li id="GUID-FBC8264B-B808-57D3-91FA-60A5C5074226"><p>compact; this makes unused space available for re-use by the relevant system pool; for example, the filing system in the case of file-based stores.</p> </li> </ul> <p>Space reclamation and compaction are only supported by the permanent file store, <codeph>CPermanentFileStore</codeph>, and are not supported by embedded or direct file stores. Because permanent file stores must maintain their integrity, even when a transaction fails, normal operations use a relatively conservative approach to update these stores without overwriting old data. Therefore, applications using permanent file stores must compact them regularly.</p> <p>The task of both space reclamation and compaction can be approached in one of two general ways:</p> <ul><li id="GUID-4F10D740-C890-51AB-80A6-6DC76FFC39AA"><p>as a single, possibly long-running, job</p> </li> <li id="GUID-53D117F5-809C-5AB2-97E8-5AD087ABB434"><p>incrementally, as a series of small steps, running either synchronously or asynchronously.</p> </li> </ul> <section><title>See also</title> <p><xref href="GUID-C9D8D913-C65F-5A69-A606-30F59BFB38E2.dita">File stores</xref> </p> </section> </conbody></concept>