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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

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

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

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

    15 <p>There are two things you can do about this:</p>

    16 <ul>

    17 <li id="GUID-4DDE58C7-78C8-5356-A7EA-FA1D24BFE327"><p>reclaim unused space;

    18 this makes it available for re-use by the store</p> </li>

    19 <li id="GUID-FBC8264B-B808-57D3-91FA-60A5C5074226"><p>compact; this makes

    20 unused space available for re-use by the relevant system pool; for example,

    21 the filing system in the case of file-based stores.</p> </li>

    22 </ul>

    23 <p>Space reclamation and compaction are only supported by the permanent file

    24 store, <codeph>CPermanentFileStore</codeph>, and are not supported by embedded

    25 or direct file stores. Because permanent file stores must maintain their integrity,

    26 even when a transaction fails, normal operations use a relatively conservative

    27 approach to update these stores without overwriting old data. Therefore, applications

    28 using permanent file stores must compact them regularly.</p>

    29 <p>The task of both space reclamation and compaction can be approached in

    30 one of two general ways:</p>

    31 <ul>

    32 <li id="GUID-4F10D740-C890-51AB-80A6-6DC76FFC39AA"><p>as a single, possibly

    33 long-running, job</p> </li>

    34 <li id="GUID-53D117F5-809C-5AB2-97E8-5AD087ABB434"><p>incrementally, as a

    35 series of small steps, running either synchronously or asynchronously.</p> </li>

    36 </ul>

    37 </conbody><related-links>

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

    39 </link>

    40 </related-links></concept>