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| <h1 class="title">TDB with 64-bit and 32-bit JVMs</h1> |
| |
| <p>TDB runs on both 32-bit and 64-bit Java Virtual Machines. The same |
| file formats are used on both systems and database files can be |
| transferred between architectures (no TDB system should be running |
| for the database at the time of copy). The difference is that a |
| different file access mechanism used.</p> |
| <p>The file access mechanism can be set explicitly, but this is not a |
| good idea for production usage, only for experimentation - see the |
| <a href="configuration.html#file_access_mode">File Access mode option</a>.</p> |
| <h2 id="64-bit-java">64-bit Java</h2> |
| <p>On 64-bit Java, TDB uses memory mapped files and the operating |
| system handles much of the caching between RAM and disk. The amount |
| of RAM used for file caching increases and decreases as other |
| application run on the machine. The fewer other programs running on |
| the machine, the more RAM will be available for file caching.</p> |
| <p>TDB is faster on a 64 bit JVM because more memory is available for |
| file caching.</p> |
| <h2 id="32-bit-java">32-bit Java</h2> |
| <p>On 32-bit Java, TDB uses its own file caching to enable large |
| databases. 32-bit Java limits the address space of the JVM to about |
| 1.5Gbytes (the exact size is JVM-dependent), and this includes |
| memory mapped files, even though they are not in the Java heap. The |
| JVM heap size may need to be increased to make space for the disk |
| caches used by TDB.</p> |
| <h2 id="disk-format">Disk Format</h2> |
| <p>The on-disk file format is compatible between 32 and 64 bit systems |
| and databases can be transferred between systems by file copy if the |
| databases are not in use (no TDB or Fuseki instance is accessing them |
| at the time). Databases can not be copied while TDB is running, even |
| if TDB is not actively processing a query or update.</p> |
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