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<div class="section" id="pytables-parameter-files">
<span id="parameter-files"></span><h1>PyTables parameter files<a class="headerlink" href="#pytables-parameter-files" title="Permalink to this headline">¶</a></h1>
<p>PyTables issues warnings when certain limits are exceeded. Those limits are
not intrinsic limitations of the underlying software, but rather are
proactive measures to avoid large resource consumptions. The default limits
should be enough for most of cases, and users should try to respect them.
However, in some situations, it can be convenient to increase (or decrease)
these limits.</p>
<p>Also, and in order to get maximum performance, PyTables implements a series
of sophisticated features, like I/O buffers or different kind of caches (for
nodes, chunks and other internal metadata). These features comes with a
default set of parameters that ensures a decent performance in most of
situations. But, as there is always a need for every case, it is handy to
have the possibility to fine-tune some of these parameters.</p>
<p>Because of these reasons, PyTables implements a couple of ways to change the
values of these parameters. All the <em>tunable</em> parameters live in the
<tt class="file docutils literal"><span class="pre">tables/parameters.py</span></tt>. The user can choose to change them in the
parameter files themselves for a global and persistent change. Moreover, if
he wants a finer control, he can pass any of these parameters directly to the
<a class="reference internal" href="libref/top_level.html#tables.open_file" title="tables.open_file"><tt class="xref py py-func docutils literal"><span class="pre">tables.open_file()</span></tt></a> function, and the new parameters will only take
effect in the corresponding file (the defaults will continue to be in the
parameter files).</p>
<p>A description of all of the tunable parameters follows. As the defaults
stated here may change from release to release, please check with your actual
parameter files so as to know your actual default values.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p>Changing the next parameters may have a very bad effect in the resource
consumption and performance of your PyTables scripts.</p>
<p class="last">Please be careful when touching these!</p>
</div>
<div class="section" id="tunable-parameters-in-parameters-py">
<h2>Tunable parameters in parameters.py<a class="headerlink" href="#tunable-parameters-in-parameters-py" title="Permalink to this headline">¶</a></h2>
<div class="section" id="recommended-maximum-values">
<h3>Recommended maximum values<a class="headerlink" href="#recommended-maximum-values" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="tables.parameters.MAX_COLUMNS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_COLUMNS</tt><em class="property"> = 512</em><a class="headerlink" href="#tables.parameters.MAX_COLUMNS" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum number of columns in <a class="reference internal" href="libref/structured_storage.html#tables.Table" title="tables.Table"><tt class="xref py py-class docutils literal"><span class="pre">tables.Table</span></tt></a> objects before a
<a class="reference internal" href="libref/helper_classes.html#tables.PerformanceWarning" title="tables.PerformanceWarning"><tt class="xref py py-exc docutils literal"><span class="pre">tables.PerformanceWarning</span></tt></a> is issued. This limit is somewhat
arbitrary and can be increased.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.MAX_NODE_ATTRS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_NODE_ATTRS</tt><em class="property"> = 4096</em><a class="headerlink" href="#tables.parameters.MAX_NODE_ATTRS" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum allowed number of attributes in a node.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.MAX_GROUP_WIDTH">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_GROUP_WIDTH</tt><em class="property"> = 16384</em><a class="headerlink" href="#tables.parameters.MAX_GROUP_WIDTH" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum allowed number of children hanging from a group.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.MAX_TREE_DEPTH">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_TREE_DEPTH</tt><em class="property"> = 2048</em><a class="headerlink" href="#tables.parameters.MAX_TREE_DEPTH" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum depth in object tree allowed.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.MAX_UNDO_PATH_LENGTH">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_UNDO_PATH_LENGTH</tt><em class="property"> = 10240</em><a class="headerlink" href="#tables.parameters.MAX_UNDO_PATH_LENGTH" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum length of paths allowed in undo/redo operations.</p>
</dd></dl>
</div>
<div class="section" id="cache-limits">
<h3>Cache limits<a class="headerlink" href="#cache-limits" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="tables.parameters.CHUNK_CACHE_NELMTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">CHUNK_CACHE_NELMTS</tt><em class="property"> = 521</em><a class="headerlink" href="#tables.parameters.CHUNK_CACHE_NELMTS" title="Permalink to this definition">¶</a></dt>
<dd><p>Number of elements for HDF5 chunk cache.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.CHUNK_CACHE_PREEMPT">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">CHUNK_CACHE_PREEMPT</tt><em class="property"> = 0.0</em><a class="headerlink" href="#tables.parameters.CHUNK_CACHE_PREEMPT" title="Permalink to this definition">¶</a></dt>
<dd><p>Chunk preemption policy. This value should be between 0 and 1
inclusive and indicates how much chunks that have been fully read are
favored for preemption. A value of zero means fully read chunks are
treated no differently than other chunks (the preemption is strictly
LRU) while a value of one means fully read chunks are always preempted
before other chunks.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.CHUNK_CACHE_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">CHUNK_CACHE_SIZE</tt><em class="property"> = 2097152</em><a class="headerlink" href="#tables.parameters.CHUNK_CACHE_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>Size (in bytes) for HDF5 chunk cache.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.COND_CACHE_SLOTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">COND_CACHE_SLOTS</tt><em class="property"> = 128</em><a class="headerlink" href="#tables.parameters.COND_CACHE_SLOTS" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum number of conditions for table queries to be kept in memory.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.METADATA_CACHE_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">METADATA_CACHE_SIZE</tt><em class="property"> = 1048576</em><a class="headerlink" href="#tables.parameters.METADATA_CACHE_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>Size (in bytes) of the HDF5 metadata cache.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.NODE_CACHE_SLOTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">NODE_CACHE_SLOTS</tt><em class="property"> = 64</em><a class="headerlink" href="#tables.parameters.NODE_CACHE_SLOTS" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum number of unreferenced nodes to be kept in memory.</p>
<p>If positive, this is the number of <em>unreferenced</em> nodes to be kept in
the metadata cache. Least recently used nodes are unloaded from memory
when this number of loaded nodes is reached. To load a node again,
simply access it as usual. Nodes referenced by user variables are not
taken into account nor unloaded.</p>
<p>Negative value means that all the touched nodes will be kept in an
internal dictionary. This is the faster way to load/retrieve nodes.
However, and in order to avoid a large memory comsumption, the user will
be warned when the number of loaded nodes will reach the
<tt class="docutils literal"><span class="pre">-NODE_CACHE_SLOTS</span></tt> value.</p>
<p>Finally, a value of zero means that any cache mechanism is disabled.</p>
</dd></dl>
</div>
<div class="section" id="parameters-for-the-different-internal-caches">
<h3>Parameters for the different internal caches<a class="headerlink" href="#parameters-for-the-different-internal-caches" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="tables.parameters.BOUNDS_MAX_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">BOUNDS_MAX_SIZE</tt><em class="property"> = 1048576</em><a class="headerlink" href="#tables.parameters.BOUNDS_MAX_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum size for bounds values cached during index lookups.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.BOUNDS_MAX_SLOTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">BOUNDS_MAX_SLOTS</tt><em class="property"> = 4096</em><a class="headerlink" href="#tables.parameters.BOUNDS_MAX_SLOTS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of slots for the BOUNDS cache.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.ITERSEQ_MAX_ELEMENTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">ITERSEQ_MAX_ELEMENTS</tt><em class="property"> = 1024</em><a class="headerlink" href="#tables.parameters.ITERSEQ_MAX_ELEMENTS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of iterator elements cached in data lookups.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.ITERSEQ_MAX_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">ITERSEQ_MAX_SIZE</tt><em class="property"> = 1048576</em><a class="headerlink" href="#tables.parameters.ITERSEQ_MAX_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum space that will take ITERSEQ cache (in bytes).</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.ITERSEQ_MAX_SLOTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">ITERSEQ_MAX_SLOTS</tt><em class="property"> = 128</em><a class="headerlink" href="#tables.parameters.ITERSEQ_MAX_SLOTS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of slots in ITERSEQ cache.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.LIMBOUNDS_MAX_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">LIMBOUNDS_MAX_SIZE</tt><em class="property"> = 262144</em><a class="headerlink" href="#tables.parameters.LIMBOUNDS_MAX_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum size for the query limits (for example, <tt class="docutils literal"><span class="pre">(lim1,</span> <span class="pre">lim2)</span></tt>
in conditions like <tt class="docutils literal"><span class="pre">lim1</span> <span class="pre"><=</span> <span class="pre">col</span> <span class="pre"><</span> <span class="pre">lim2</span></tt>) cached during index lookups
(in bytes).</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.LIMBOUNDS_MAX_SLOTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">LIMBOUNDS_MAX_SLOTS</tt><em class="property"> = 128</em><a class="headerlink" href="#tables.parameters.LIMBOUNDS_MAX_SLOTS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of slots for LIMBOUNDS cache.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.TABLE_MAX_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">TABLE_MAX_SIZE</tt><em class="property"> = 1048576</em><a class="headerlink" href="#tables.parameters.TABLE_MAX_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum size for table chunks cached during index queries.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.SORTED_MAX_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">SORTED_MAX_SIZE</tt><em class="property"> = 1048576</em><a class="headerlink" href="#tables.parameters.SORTED_MAX_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum size for sorted values cached during index lookups.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.SORTEDLR_MAX_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">SORTEDLR_MAX_SIZE</tt><em class="property"> = 8388608</em><a class="headerlink" href="#tables.parameters.SORTEDLR_MAX_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum size for chunks in last row cached in index lookups (in
bytes).</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.SORTEDLR_MAX_SLOTS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">SORTEDLR_MAX_SLOTS</tt><em class="property"> = 1024</em><a class="headerlink" href="#tables.parameters.SORTEDLR_MAX_SLOTS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of chunks for SORTEDLR cache.</p>
</dd></dl>
</div>
<div class="section" id="parameters-for-general-cache-behaviour">
<h3>Parameters for general cache behaviour<a class="headerlink" href="#parameters-for-general-cache-behaviour" title="Permalink to this headline">¶</a></h3>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">The next parameters will not take any effect if passed to the open_file()
function, so they can only be changed in a <em>global</em> way. You can change
them in the file, but this is strongly discouraged unless you know well
what you are doing.</p>
</div>
<dl class="data">
<dt id="tables.parameters.DISABLE_EVERY_CYCLES">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DISABLE_EVERY_CYCLES</tt><em class="property"> = 10</em><a class="headerlink" href="#tables.parameters.DISABLE_EVERY_CYCLES" title="Permalink to this definition">¶</a></dt>
<dd><p>The number of cycles in which a cache will be forced to be disabled
if the hit ratio is lower than the LOWEST_HIT_RATIO (see below). This
value should provide time enough to check whether the cache is being
efficient or not.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.ENABLE_EVERY_CYCLES">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">ENABLE_EVERY_CYCLES</tt><em class="property"> = 50</em><a class="headerlink" href="#tables.parameters.ENABLE_EVERY_CYCLES" title="Permalink to this definition">¶</a></dt>
<dd><p>The number of cycles in which a cache will be forced to be
(re-)enabled, irregardingly of the hit ratio. This will provide a chance
for checking if we are in a better scenario for doing caching again.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.LOWEST_HIT_RATIO">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">LOWEST_HIT_RATIO</tt><em class="property"> = 0.6</em><a class="headerlink" href="#tables.parameters.LOWEST_HIT_RATIO" title="Permalink to this definition">¶</a></dt>
<dd><p>The minimum acceptable hit ratio for a cache to avoid disabling (and
freeing) it.</p>
</dd></dl>
</div>
<div class="section" id="parameters-for-the-i-o-buffer-in-leaf-objects">
<h3>Parameters for the I/O buffer in Leaf objects<a class="headerlink" href="#parameters-for-the-i-o-buffer-in-leaf-objects" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="tables.parameters.IO_BUFFER_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">IO_BUFFER_SIZE</tt><em class="property"> = 1048576</em><a class="headerlink" href="#tables.parameters.IO_BUFFER_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>The PyTables internal buffer size for I/O purposes. Should not
exceed the amount of highest level cache size in your CPU.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.BUFFER_TIMES">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">BUFFER_TIMES</tt><em class="property"> = 100</em><a class="headerlink" href="#tables.parameters.BUFFER_TIMES" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum buffersize/rowsize ratio before issuing a
<a class="reference internal" href="libref/helper_classes.html#tables.PerformanceWarning" title="tables.PerformanceWarning"><tt class="xref py py-exc docutils literal"><span class="pre">tables.PerformanceWarning</span></tt></a>.</p>
</dd></dl>
</div>
<div class="section" id="miscellaneous">
<h3>Miscellaneous<a class="headerlink" href="#miscellaneous" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="tables.parameters.EXPECTED_ROWS_EARRAY">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">EXPECTED_ROWS_EARRAY</tt><em class="property"> = 1000</em><a class="headerlink" href="#tables.parameters.EXPECTED_ROWS_EARRAY" title="Permalink to this definition">¶</a></dt>
<dd><p>Default expected number of rows for <tt class="xref py py-class docutils literal"><span class="pre">EArray</span></tt> objects.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.EXPECTED_ROWS_TABLE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">EXPECTED_ROWS_TABLE</tt><em class="property"> = 10000</em><a class="headerlink" href="#tables.parameters.EXPECTED_ROWS_TABLE" title="Permalink to this definition">¶</a></dt>
<dd><p>Default expected number of rows for <tt class="xref py py-class docutils literal"><span class="pre">Table</span></tt> objects.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.PYTABLES_SYS_ATTRS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">PYTABLES_SYS_ATTRS</tt><em class="property"> = True</em><a class="headerlink" href="#tables.parameters.PYTABLES_SYS_ATTRS" title="Permalink to this definition">¶</a></dt>
<dd><p>Set this to <tt class="docutils literal"><span class="pre">False</span></tt> if you don’t want to create PyTables system
attributes in datasets. Also, if set to <tt class="docutils literal"><span class="pre">False</span></tt> the possible existing
system attributes are not considered for guessing the class of the node
during its loading from disk (this work is delegated to the PyTables’
class discoverer function for general HDF5 files).</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.MAX_NUMEXPR_THREADS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_NUMEXPR_THREADS</tt><em class="property"> = None</em><a class="headerlink" href="#tables.parameters.MAX_NUMEXPR_THREADS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of threads that PyTables should use internally in
Numexpr. If <cite>None</cite>, it is automatically set to the number of cores in
your machine. In general, it is a good idea to set this to the number of
cores in your machine or, when your machine has many of them (e.g. > 4),
perhaps one less than this.</p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.MAX_BLOSC_THREADS">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">MAX_BLOSC_THREADS</tt><em class="property"> = None</em><a class="headerlink" href="#tables.parameters.MAX_BLOSC_THREADS" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of threads that PyTables should use internally in
Blosc. If <cite>None</cite>, it is automatically set to the number of cores in
your machine. In general, it is a good idea to set this to the number of
cores in your machine or, when your machine has many of them (e.g. > 4),
perhaps one less than this.</p>
</dd></dl>
</div>
<div class="section" id="hdf5-driver-management">
<h3>HDF5 driver management<a class="headerlink" href="#hdf5-driver-management" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="tables.parameters.DRIVER">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER</tt><em class="property"> = None</em><a class="headerlink" href="#tables.parameters.DRIVER" title="Permalink to this definition">¶</a></dt>
<dd><p>The HDF5 driver that should be used for reading/writing to the file.</p>
<p>Following drivers are supported:</p>
<blockquote>
<div><ul class="simple">
<li>H5FD_SEC2: this driver uses POSIX file-system functions like read
and write to perform I/O to a single, permanent file on local
disk with no system buffering.
This driver is POSIX-compliant and is the default file driver for
all systems.</li>
<li>H5FD_DIRECT: this is the H5FD_SEC2 driver except data is written
to or read from the file synchronously without being cached by
the system.</li>
<li>H5FD_WINDOWS: this driver was modified in HDF5-1.8.8 to be a
wrapper of the POSIX driver, H5FD_SEC2. This change should not
affect user applications.</li>
<li>H5FD_STDIO: this driver uses functions from the standard C
stdio.h to perform I/O to a single, permanent file on local disk
with additional system buffering.</li>
<li>H5FD_CORE: with this driver, an application can work with a file
in memory for faster reads and writes. File contents are kept in
memory until the file is closed. At closing, the memory version
of the file can be written back to disk or abandoned.</li>
</ul>
</div></blockquote>
<p>The following drivers are not currently supported:</p>
<blockquote>
<div><ul class="simple">
<li>H5FD_LOG: this is the H5FD_SEC2 driver with logging capabilities.</li>
<li>H5FD_FAMILY: with this driver, the HDF5 file’s address space is
partitioned into pieces and sent to separate storage files using
an underlying driver of the user’s choice.
This driver is for systems that do not support files larger than
2 gigabytes.</li>
<li>H5FD_MULTI: with this driver, data can be stored in multiple
files according to the type of the data. I/O might work better if
data is stored in separate files based on the type of data.
The Split driver is a special case of this driver.</li>
<li>H5FD_SPLIT: this file driver splits a file into two parts.
One part stores metadata, and the other part stores raw data.
This splitting a file into two parts is a limited case of the
Multi driver.</li>
<li>H5FD_MPIO: this is the standard HDF5 file driver for parallel
file systems. This driver uses the MPI standard for both
communication and file I/O.</li>
<li>H5FD_MPIPOSIX: this parallel file system driver uses MPI for
communication and POSIX file-system calls for file I/O.</li>
<li>H5FD_STREAM: this driver is no longer available.</li>
</ul>
</div></blockquote>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">the <a class="reference external" href="http://www.hdfgroup.org/HDF5/doc/UG/08_TheFile.html#Drivers">Drivers section</a> of the <a class="reference external" href="http://www.hdfgroup.org/HDF5/doc/UG/index.html">HDF5 User’s Guide</a> for
more information.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>not all supported drivers are always available. For example the
H5FD_WINDOWS driver is not available on non Windows platforms.</p>
<p class="last">If the user try to use a driver that is not available on the target
platform a <tt class="xref py py-exc docutils literal"><span class="pre">RuntimeError</span></tt> is raised.</p>
</div>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.DRIVER_DIRECT_ALIGNMENT">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER_DIRECT_ALIGNMENT</tt><em class="property"> = 0</em><a class="headerlink" href="#tables.parameters.DRIVER_DIRECT_ALIGNMENT" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies the required alignment boundary in memory.</p>
<p>A value of 0 (zero) means to use HDF5 Library’s default value.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.DRIVER_DIRECT_BLOCK_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER_DIRECT_BLOCK_SIZE</tt><em class="property"> = 0</em><a class="headerlink" href="#tables.parameters.DRIVER_DIRECT_BLOCK_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies the file system block size.</p>
<p>A value of 0 (zero) means to use HDF5 Library’s default value of 4KB.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.DRIVER_DIRECT_CBUF_SIZE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER_DIRECT_CBUF_SIZE</tt><em class="property"> = 0</em><a class="headerlink" href="#tables.parameters.DRIVER_DIRECT_CBUF_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies the copy buffer size.</p>
<p>A value of 0 (zero) means to use HDF5 Library’s default value.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.DRIVER_CORE_INCREMENT">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER_CORE_INCREMENT</tt><em class="property"> = 65536</em><a class="headerlink" href="#tables.parameters.DRIVER_CORE_INCREMENT" title="Permalink to this definition">¶</a></dt>
<dd><p>Core driver memory increment.</p>
<p>Specifies the increment by which allocated memory is to be increased
each time more memory is required.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.DRIVER_CORE_BACKING_STORE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER_CORE_BACKING_STORE</tt><em class="property"> = 1</em><a class="headerlink" href="#tables.parameters.DRIVER_CORE_BACKING_STORE" title="Permalink to this definition">¶</a></dt>
<dd><p>Enables backing store for the core driver.</p>
<p>With the H5FD_CORE driver, if the DRIVER_CORE_BACKING_STORE is set
to 1 (True), the file contents are flushed to a file with the same name
as this core file when the file is closed or access to the file is
terminated in memory.</p>
<p>The application is allowed to open an existing file with H5FD_CORE
driver. In that case, if the DRIVER_CORE_BACKING_STORE is set to 1 and
the flags for <a class="reference internal" href="libref/top_level.html#tables.open_file" title="tables.open_file"><tt class="xref py py-func docutils literal"><span class="pre">tables.open_file()</span></tt></a> is set to H5F_ACC_RDWR, any change
to the file contents are saved to the file when the file is closed.
If backing_store is set to 0 and the flags for <a class="reference internal" href="libref/top_level.html#tables.open_file" title="tables.open_file"><tt class="xref py py-func docutils literal"><span class="pre">tables.open_file()</span></tt></a>
is set to H5F_ACC_RDWR, any change to the file contents will be lost
when the file is closed. If the flags for <a class="reference internal" href="libref/top_level.html#tables.open_file" title="tables.open_file"><tt class="xref py py-func docutils literal"><span class="pre">tables.open_file()</span></tt></a> is
set to H5F_ACC_RDONLY, no change to the file is allowed either in
memory or on file.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
<dl class="data">
<dt id="tables.parameters.DRIVER_CORE_IMAGE">
<tt class="descclassname">tables.parameters.</tt><tt class="descname">DRIVER_CORE_IMAGE</tt><em class="property"> = None</em><a class="headerlink" href="#tables.parameters.DRIVER_CORE_IMAGE" title="Permalink to this definition">¶</a></dt>
<dd><p>String containing an HDF5 file image.</p>
<p>If this oprion is passed to the <a class="reference internal" href="libref/top_level.html#tables.open_file" title="tables.open_file"><tt class="xref py py-func docutils literal"><span class="pre">tables.open_file()</span></tt></a> function then the
returned file object is set up using the specified image.</p>
<p>A file image can be retrieved from an existing (and opened) file object
using the <a class="reference internal" href="libref/file_class.html#tables.File.get_file_image" title="tables.File.get_file_image"><tt class="xref py py-meth docutils literal"><span class="pre">tables.File.get_file_image()</span></tt></a> method.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">requires HDF5 >= 1.8.9.</p>
</div>
<p class="versionadded">
<span class="versionmodified">New in version 3.0.</span></p>
</dd></dl>
</div>
</div>
</div>
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<h3><a href="../index.html">Table Of Contents</a></h3>
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<li><a class="reference internal" href="#">PyTables parameter files</a><ul>
<li><a class="reference internal" href="#tunable-parameters-in-parameters-py">Tunable parameters in parameters.py</a><ul>
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<li><a class="reference internal" href="#parameters-for-the-i-o-buffer-in-leaf-objects">Parameters for the I/O buffer in Leaf objects</a></li>
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