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| <section id="environment-variables"> |
| <span id="cpp-env-vars"></span><h1>Environment Variables<a class="headerlink" href="#environment-variables" title="Permalink to this heading">#</a></h1> |
| <p>The following environment variables can be used to affect the behavior of |
| Arrow C++ at runtime. Many of these variables are inspected only once per |
| process (for example, when the Arrow C++ DLL is loaded), so you cannot assume |
| that changing their value later will have an effect.</p> |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ACERO_ALIGNMENT_HANDLING"> |
| <span class="sig-name descname"><span class="pre">ACERO_ALIGNMENT_HANDLING</span></span><a class="headerlink" href="#envvar-ACERO_ALIGNMENT_HANDLING" title="Permalink to this definition">#</a></dt> |
| <dd><p>Arrow C++’s Acero module performs computation on streams of data. This |
| computation may involve a form of “type punning” that is technically |
| undefined behavior if the underlying array is not properly aligned. On |
| most modern CPUs this is not an issue, but some older CPUs may crash or |
| suffer poor performance. For this reason it is recommended that all |
| incoming array buffers are properly aligned, but some data sources |
| such as <a class="reference internal" href="../format/Flight.html#flight-rpc"><span class="std std-ref">Flight</span></a> may produce unaligned buffers.</p> |
| <p>The value of this environment variable controls what will happen when |
| Acero detects an unaligned buffer:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">warn</span></code>: a warning is emitted</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ignore</span></code>: nothing, alignment checking is disabled</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">reallocate</span></code>: the buffer is reallocated to a properly aligned address</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">error</span></code>: the operation fails with an error</p></li> |
| </ul> |
| <p>The default behavior is <code class="docutils literal notranslate"><span class="pre">warn</span></code>. On modern hardware it is usually safe |
| to change this to <code class="docutils literal notranslate"><span class="pre">ignore</span></code>. Changing to <code class="docutils literal notranslate"><span class="pre">reallocate</span></code> is the safest |
| option but this will have a significant performance impact as the buffer |
| will need to be copied.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_DEBUG_MEMORY_POOL"> |
| <span class="sig-name descname"><span class="pre">ARROW_DEBUG_MEMORY_POOL</span></span><a class="headerlink" href="#envvar-ARROW_DEBUG_MEMORY_POOL" title="Permalink to this definition">#</a></dt> |
| <dd><p>Enable rudimentary memory checks to guard against buffer overflows. |
| The value of this environment variable selects the behavior when a |
| buffer overflow is detected:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">abort</span></code> exits the processus with a non-zero return value;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">trap</span></code> issues a platform-specific debugger breakpoint / trap instruction;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">warn</span></code> prints a warning on stderr and continues execution;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">none</span></code> disables memory checks;</p></li> |
| </ul> |
| <p>If this variable is not set, or has an empty value, it has the same effect |
| as the value <code class="docutils literal notranslate"><span class="pre">none</span></code> - memory checks are disabled.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>While this functionality can be useful and has little overhead, it |
| is not a replacement for more sophisticated memory checking utilities |
| such as <a class="reference external" href="https://valgrind.org/">Valgrind</a> or |
| <a class="reference external" href="https://clang.llvm.org/docs/AddressSanitizer.html">Address Sanitizer</a>.</p> |
| </div> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_DEFAULT_MEMORY_POOL"> |
| <span class="sig-name descname"><span class="pre">ARROW_DEFAULT_MEMORY_POOL</span></span><a class="headerlink" href="#envvar-ARROW_DEFAULT_MEMORY_POOL" title="Permalink to this definition">#</a></dt> |
| <dd><p>Override the backend to be used for the default |
| <a class="reference internal" href="memory.html#cpp-memory-pool"><span class="std std-ref">memory pool</span></a>. Possible values are among <code class="docutils literal notranslate"><span class="pre">jemalloc</span></code>, |
| <code class="docutils literal notranslate"><span class="pre">mimalloc</span></code> and <code class="docutils literal notranslate"><span class="pre">system</span></code>, depending on which backends were enabled when |
| <a class="reference internal" href="../developers/cpp/building.html#building-arrow-cpp"><span class="std std-ref">building Arrow C++</span></a>.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_IO_THREADS"> |
| <span class="sig-name descname"><span class="pre">ARROW_IO_THREADS</span></span><a class="headerlink" href="#envvar-ARROW_IO_THREADS" title="Permalink to this definition">#</a></dt> |
| <dd><p>Override the default number of threads for the global IO thread pool. |
| The value of this environment variable should be a positive integer.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_LIBHDFS_DIR"> |
| <span class="sig-name descname"><span class="pre">ARROW_LIBHDFS_DIR</span></span><a class="headerlink" href="#envvar-ARROW_LIBHDFS_DIR" title="Permalink to this definition">#</a></dt> |
| <dd><p>The directory containing the C HDFS library (<code class="docutils literal notranslate"><span class="pre">hdfs.dll</span></code> on Windows, |
| <code class="docutils literal notranslate"><span class="pre">libhdfs.dylib</span></code> on macOS, <code class="docutils literal notranslate"><span class="pre">libhdfs.so</span></code> on other platforms). |
| Alternatively, one can set <span class="target" id="index-0"></span><a class="reference internal" href="#envvar-HADOOP_HOME"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">HADOOP_HOME</span></code></a>.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_S3_LOG_LEVEL"> |
| <span class="sig-name descname"><span class="pre">ARROW_S3_LOG_LEVEL</span></span><a class="headerlink" href="#envvar-ARROW_S3_LOG_LEVEL" title="Permalink to this definition">#</a></dt> |
| <dd><p>Controls the verbosity of logging produced by S3 calls. Defaults to <code class="docutils literal notranslate"><span class="pre">FATAL</span></code> |
| which only produces output in the case of fatal errors. <code class="docutils literal notranslate"><span class="pre">DEBUG</span></code> is recommended |
| when you’re trying to troubleshoot issues.</p> |
| <p>Possible values include:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">FATAL</span></code> (the default)</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ERROR</span></code></p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">WARN</span></code></p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">INFO</span></code></p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">DEBUG</span></code></p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">TRACE</span></code></p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">OFF</span></code></p></li> |
| </ul> |
| <div class="admonition seealso"> |
| <p class="admonition-title">See also</p> |
| <p><a class="reference external" href="https://docs.aws.amazon.com/sdk-for-cpp/v1/developer-guide/logging.html">Logging - AWS SDK For C++</a></p> |
| </div> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_TRACING_BACKEND"> |
| <span class="sig-name descname"><span class="pre">ARROW_TRACING_BACKEND</span></span><a class="headerlink" href="#envvar-ARROW_TRACING_BACKEND" title="Permalink to this definition">#</a></dt> |
| <dd><p>The backend where to export <a class="reference external" href="https://opentelemetry.io/">OpenTelemetry</a>-based |
| execution traces. Possible values are:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ostream</span></code>: emit textual log messages to stdout;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">otlp_http</span></code>: emit OTLP JSON encoded traces to a HTTP server (by default, |
| the endpoint URL is “<a class="reference external" href="http://localhost:4318/v1/traces">http://localhost:4318/v1/traces</a>”);</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">arrow_otlp_stdout</span></code>: emit JSON traces to stdout;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">arrow_otlp_stderr</span></code>: emit JSON traces to stderr.</p></li> |
| </ul> |
| <p>If this variable is not set, no traces are exported.</p> |
| <p>This environment variable has no effect if Arrow C++ was not built with |
| tracing enabled.</p> |
| <div class="admonition seealso"> |
| <p class="admonition-title">See also</p> |
| <p><a class="reference external" href="https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md">OpenTelemetry configuration for remote endpoints</a></p> |
| </div> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-ARROW_USER_SIMD_LEVEL"> |
| <span class="sig-name descname"><span class="pre">ARROW_USER_SIMD_LEVEL</span></span><a class="headerlink" href="#envvar-ARROW_USER_SIMD_LEVEL" title="Permalink to this definition">#</a></dt> |
| <dd><p>The maximum SIMD optimization level selectable at runtime. Useful for |
| comparing the performance impact of enabling or disabling respective code |
| paths or working around situations where instructions are supported but are |
| not performant or cause other issues.</p> |
| <p>By default, Arrow C++ detects the capabilities of the current CPU at runtime |
| and chooses the best execution paths based on that information. This |
| behavior can be overriden by setting this environment variable to a |
| well-defined value. Supported values are:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">NONE</span></code> disables any runtime-selected SIMD optimization;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">SSE4_2</span></code> enables any SSE2-based optimizations until SSE4.2 (included);</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">AVX</span></code> enables any AVX-based optimizations and earlier;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">AVX2</span></code> enables any AVX2-based optimizations and earlier;</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">AVX512</span></code> enables any AVX512-based optimizations and earlier.</p></li> |
| </ul> |
| <p>This environment variable only has an effect on x86 platforms. Other |
| platforms currently do not implement any form of runtime dispatch.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>In addition to runtime-selected SIMD optimizations dispatch, Arrow C++ can |
| also be compiled with SIMD optimizations that cannot be disabled at |
| runtime. For example, by default, SSE4.2 optimizations are enabled on x86 |
| builds: therefore, with this default setting, Arrow C++ does not work at |
| all on a CPU without support for SSE4.2. This setting can be changed |
| using the <code class="docutils literal notranslate"><span class="pre">ARROW_SIMD_LEVEL</span></code> CMake variable so as to either raise or |
| lower the optimization level.</p> |
| <p>Finally, the <code class="docutils literal notranslate"><span class="pre">ARROW_RUNTIME_SIMD_LEVEL</span></code> CMake variable sets a |
| compile-time upper bound to runtime-selected SIMD optimizations. This is |
| useful in cases where a compiler reports support for an instruction set |
| but does not actually support it in full.</p> |
| </div> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-AWS_ENDPOINT_URL"> |
| <span class="sig-name descname"><span class="pre">AWS_ENDPOINT_URL</span></span><a class="headerlink" href="#envvar-AWS_ENDPOINT_URL" title="Permalink to this definition">#</a></dt> |
| <dd><p>Endpoint URL used for S3-like storage, for example Minio or s3.scality. |
| Alternatively, one can set <span class="target" id="index-1"></span><a class="reference internal" href="#envvar-AWS_ENDPOINT_URL_S3"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">AWS_ENDPOINT_URL_S3</span></code></a>.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-AWS_ENDPOINT_URL_S3"> |
| <span class="sig-name descname"><span class="pre">AWS_ENDPOINT_URL_S3</span></span><a class="headerlink" href="#envvar-AWS_ENDPOINT_URL_S3" title="Permalink to this definition">#</a></dt> |
| <dd><p>Endpoint URL used for S3-like storage, for example Minio or s3.scality. |
| This takes precedence over <span class="target" id="index-2"></span><a class="reference internal" href="#envvar-AWS_ENDPOINT_URL"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">AWS_ENDPOINT_URL</span></code></a> if both variables |
| are set.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-GANDIVA_CACHE_SIZE"> |
| <span class="sig-name descname"><span class="pre">GANDIVA_CACHE_SIZE</span></span><a class="headerlink" href="#envvar-GANDIVA_CACHE_SIZE" title="Permalink to this definition">#</a></dt> |
| <dd><p>The number of entries to keep in the Gandiva JIT compilation cache. |
| The cache is in-memory and does not persist across processes.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-HADOOP_HOME"> |
| <span class="sig-name descname"><span class="pre">HADOOP_HOME</span></span><a class="headerlink" href="#envvar-HADOOP_HOME" title="Permalink to this definition">#</a></dt> |
| <dd><p>The path to the Hadoop installation.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-JAVA_HOME"> |
| <span class="sig-name descname"><span class="pre">JAVA_HOME</span></span><a class="headerlink" href="#envvar-JAVA_HOME" title="Permalink to this definition">#</a></dt> |
| <dd><p>Set the path to the Java Runtime Environment installation. This may be |
| required for HDFS support if Java is installed in a non-standard location.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-OMP_NUM_THREADS"> |
| <span class="sig-name descname"><span class="pre">OMP_NUM_THREADS</span></span><a class="headerlink" href="#envvar-OMP_NUM_THREADS" title="Permalink to this definition">#</a></dt> |
| <dd><p>The number of worker threads in the global (process-wide) CPU thread pool. |
| If this environment variable is not defined, the available hardware |
| concurrency is determined using a platform-specific routine.</p> |
| </dd></dl> |
| |
| <dl class="std envvar"> |
| <dt class="sig sig-object std" id="envvar-OMP_THREAD_LIMIT"> |
| <span class="sig-name descname"><span class="pre">OMP_THREAD_LIMIT</span></span><a class="headerlink" href="#envvar-OMP_THREAD_LIMIT" title="Permalink to this definition">#</a></dt> |
| <dd><p>An upper bound for the number of worker threads in the global |
| (process-wide) CPU thread pool.</p> |
| <p>For example, if the current machine has 4 hardware threads and |
| <code class="docutils literal notranslate"><span class="pre">OMP_THREAD_LIMIT</span></code> is 8, the global CPU thread pool will have 4 worker |
| threads. But if <code class="docutils literal notranslate"><span class="pre">OMP_THREAD_LIMIT</span></code> is 2, the global CPU thread pool |
| will have 2 worker threads.</p> |
| </dd></dl> |
| |
| </section> |
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