Configure this via env variable

OPENPMD_BP5_GROUPENCODING_MAX_STEPS=1000

Author: franzpoeschel

include/openPMD/IO/ADIOS/ADIOS2File.hpp

@@ -25,6 +25,7 @@
 #include "openPMD/IO/IOTask.hpp"
 #include "openPMD/IO/InvalidatableFile.hpp"
 #include "openPMD/config.hpp"
+#include <optional>
 
 #if openPMD_HAVE_ADIOS2
 #include <adios2.h>
@@ -428,6 +429,7 @@ class ADIOS2File
      */
     size_t m_currentStep = 0;
     bool useStepSelection = false;
+    std::optional<size_t> m_max_steps_bp5 = std::make_optional<size_t>(1000);
 
     /*
      * ADIOS2 does not give direct access to its internal attribute and

src/IO/ADIOS/ADIOS2File.cpp

@@ -1251,17 +1251,37 @@ AdvanceStatus ADIOS2File::advance(AdvanceMode mode)
             return engineType == "bp5writer";
         };
 
+        if (this->m_currentStep == 0)
+        {
+            int max_steps_from_env =
+                auxiliary::getEnvNum("OPENPMD_BP5_GROUPENCODING_MAX_STEPS", -1);
+            if (max_steps_from_env == 0)
+            {
+                m_max_steps_bp5 = std::nullopt;
+            }
+            else if (max_steps_from_env != -1)
+            {
+                m_max_steps_bp5 =
+                    std::make_optional<size_t>(size_t(max_steps_from_env));
+            }
+        }
+
         // Check some conditions on which to now cancel operation due to
         // unwieldy metadata sizes in BP5 with group encoding
         if (this->m_impl->m_handler->m_encoding ==
                 IterationEncoding::groupBased &&
-            this->m_currentStep >= 1000 &&
+            this->m_max_steps_bp5.has_value() &&
+            this->m_currentStep >= *this->m_max_steps_bp5 &&
             (this->m_mode == adios2::Mode::Write ||
              this->m_mode == adios2::Mode::Append) &&
             check_bp5())
         {
-            throw error::OperationUnsupportedInBackend("ADIOS2", R"(
-Trying to create group-based output with more than 1000 steps in BP5 engine.
+            throw error::OperationUnsupportedInBackend(
+                "ADIOS2",
+                R"(
+Trying to create group-based output with more than )" +
+                    std::to_string(*this->m_max_steps_bp5) +
+                    R"( steps in BP5 engine.
 As this engine is not adequate for group encoding, this will create immense
 metadata sizes. For more context, check:
 
@@ -1278,7 +1298,11 @@ Please consider using either of the following instead:
 * (experimental) variable encoding (e.g. by `Series::setIterationEncoding()`
   or by the JSON config {"iteration_encoding": "variable_based"}).
   Note that there is at this point no complete read support for variable-encoded
-  outputs.)");
+  outputs.
+
+Use the environment variable OPENPMD_BP5_GROUPENCODING_MAX_STEPS to adjust the
+number of allowed steps. Set the value as 0 to disable this check.
+Be aware of the performance implications described above.)");
         }
 
         if (streamStatus != StreamStatus::DuringStep)