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<concept id="GUID-1824B323-AAA8-5403-A4CF-D1F530CBDAF5" xml:lang="en"><title>Introduction

to Space Reclamation and Compaction</title><shortdesc>When a stream is replaced or deleted, the space it occupies is

not immediately available for re-use by other streams. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>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>

</conbody><related-links>

<link href="GUID-C9D8D913-C65F-5A69-A606-30F59BFB38E2.dita"><linktext>File Stores</linktext>

</link>

</related-links></concept>