TAO/docs/releasenotes/PSS.html

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   6       <title>Persistent State Service status</title>
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  12         <h1><a name="orb"></a>Persistent State Service</h1>
  13         Points of contact: <a href="mailto: gontla_p@ociweb.com">Priyanka Gontla</a>
  14
  15         <p>Last Update: 2002/07/29 </p>
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  18       <p>Persistent State Service (PSS) describes a way of making a
  19         service persistent. The fact that PSS is being used by a
  20         service is known only to the service (server) and not to the
  21         client which makes use of the service. PSS presents persistent
  22         information as storage objects stored in storage homes, to
  23         quote the specification. The storage homes are the datastores
  24         where the persistent data is saved. </p>
  25       <br>
  26       <p>The specification introduced Persistent State Definition
  27         Language (PSDL), a superset of IDL with five new
  28         constructs. PSDL is used to specify the interface to the
  29         datastore. The PSDL file used in the application will define
  30         the types that might be saved in the datastore. </p>
  31       <br>
  32       <p>We have a compiler, psdl_tao, which is similar to the tao_idl
  33         compiler, which will process the psdl file and generate stubs
  34         that are used mainly for the insertion and extraction
  35         operations.
  36       </p>
  37
  38       <a name="current"><h3>Current status:</h3></a>
  39
  40       <ul>
  41         <li><p>The PSDL compiler understands and supports the simple
  42             types like <br><CODE>
  43               typdef, module, structures, interfaces.</CODE>
  44           </p>
  45         </li>
  46         <li>
  47           <p> The datastore for now is a regular file. The
  48             <CODE>libTAO_PSDL_Datastore</CODE> interfaces the
  49             datastore and helps write and read from the datastore.
  50             The data that is saved persistently is a hash map whose
  51             external id is TAO_PSDL_String, a wrapper around
  52             ACE_CString and the internal id is TAO_PSDL_OctetSeq, a
  53             wrapper around for CORBA::OctetSeq. </p>
  54         </li>
  55         <li>
  56           <p> There is an example in
  57             $TAO_ROOT/orbsvcs/examples/PSS which shows how the PSS
  58             can be used to make a simplified naming service persistent.
  59           </p>
  60         </li>
  61       </ul>
  62
  63       <a name="future"><h3>Future work:</h3></a>
  64
  65       <ul>
  66         <li>
  67           <p>Add support to the remaining types defined in PSDL.
  68           </p>
  69         </li>
  70
  71         <li>
  72           <p>Use RMCast to have another form of persistency via data
  73             replication.
  74           </p>
  75         </li>
  76
  77       </ul>
  78
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