1.15.0.md

July 1, 2026 ยท View on GitHub

PnetCDF Version 1.15.0 Release Notes (July 1, 2026)

  • New feature

    • Intra-node aggregation for read requests is added. This is the complement to the write counterpart first added to version 1.14.0. Now the intra-node aggregation feature supports both write and read operations. This feature can be enabled by setting hint nc_num_aggrs_per_node to the desired number of aggregators per compute node.

  • New optimization

    • When creating a new file on the Lustre file system, PnetCDF will try to set the Lustre file striping count to the number of compute nodes (NUMA nodes) allocated to the MPI communicator passed to the call of ncmpi_create(). See the section of "New PnetCDF Hints" below for more information.

  • New I/O driver

    • A submodule named "GIO" has been added as the PnetCDF's default I/O driver. PnetCDF has been using MPI-IO as its only I/O driver since its first release. With the GIO driver, PnetCDF users now have an additional option to tune the performance. GIO is a parallel I/O library, sharing the design concept of the MPI-IO. GIO implements several performance improvement, such as:
      • automatically sets cb_nodes based on the number of compute nodes and number of MPI processes running per node.
      • supports hint cb_buffer_size to be a multiple of file striping unit size for Lustre.
      • supports Lustre overstriping through hint overstriping_ratio. See the "New PnetCDF hints" section below.

  • New configure options

    • --disable-gio disables the GIO driver and uses MPI-IO. The default is to enable using the GIO driver.

  • APIs deprecated

    • The "vard" family APIs introduced in version 1.6.0 are now deprecated. These are the APIs that take an argument of MPI derived data type describing the file access layout, which is used to set the fileview through a call to MPI_File_set_view(). The deprecation is because direct file access can be a security risk and error prone.
      • ncmpi_get_vard()
      • ncmpi_get_vard_all()
      • ncmpi_put_vard()
      • ncmpi_put_vard_all()

  • API semantics updates

    • API ncmpi_inq_header_size() now can be called in the define mode. This API returns the file header size with metadata defined by the time of the call. The inquired file header size can be helpful to pick proper values for arguments h_minfree, v_align, v_minfree, r_align when calling API ncmpi__enddef() which can allow to preserve a sufficiently large free space for file header extent and variable data sections to grow later without moving data already stored in the file, i.e. when adding new variables, dimensions, or attributes. See PR #201.

  • New error code

    • NC_EDRIVER indicates an invalid PnetCDF I/O driver is set in I/O hint, nc_driver. The current valid drivers are "gio" and "mpiio".
    • NC_EFSTYPE indicates a PnetCDF internal error when an invalid file system type is detected.
    • NC_EFILEVIEW indicates a PnetCDF internal error when creating an MPI fileview whose offsets violate the MPI standard requirement of being in a monotonically non-decreasing order.

  • New PnetCDF hints

    • nc_data_move_chunk_size -- When adding new data objects into an existing file, the data sections may need to be moved to a higher file offset. The movement is performed in chunks. This hint allows users to customized the chunk size. The default is 1048576 bytes, i.e. 1 MiB. See PR #203.
    • file_striping -- When creating a new file on the Lustre file system, this hint advises PnetCDF to set the new file's striping configuration. The hint value is either "auto" or "inherit". The default is "auto". The former sets the new file's striping unit size to 1 MiB and striping count to the number of compute nodes found in the MPI communicator passed to the call of ncmpi_create(). The latter sets the striping to inherit the new file's parent folder's settings, if the folder's striping has been set. Note that if users also set the MPI-IO hint striping_factor or striping_unit, then these MPI-IO hints will take a higher precedence. See PR #222.
    • nc_driver -- To select an internal I/O driver. The value is either string "gio" or "mpiio". The default is "gio", which advises PnetCDF to use the GIO driver, an external library built as a sub-module of PnetCDF. The other is "mpiio", advising PnetCDF to use the MPI-IO driver.
    • overstriping_ratio -- This hint is passed to the GIO driver and instructs it to make use of Lustre's overstriping feature which allows to create a new file to have more than one stripe per OST. For instance, when hints striping_factor and overstriping_ratio are set to 16 and 2, respectively, the newly created file will be striped across 16/2=8 OSTs. The advantage of Lustre overstriping is to allow a file's striping count to be larger than the total number of OTS available on the system.

  • New run-time environment variables

    • GIO_ONLY - when testing PnetCDF by running command make check and make ptest, setting this environment variable will run all the tests using the default GIO driver and skip MPI-IO driver. Without setting this environment variable, the default is to test both I/O drivers. Note this environment variable only affect when testing PnetCDF and takes no effect on PnetCDF library itself.

  • Build recipes

    • doc/NERSC.md - note for building PnetCDF on machines at NERSC
    • doc/ALCF.md - note for building PnetCDF on machines at ALCF

  • Updated utility programs

    • pnetcdf_version - add information about MPI compiler vendors, supported MPI standard version, names of base compilers, and LMOD PrgEnv module loaded if available.
    • ncmpidiff now will error out when the two input file names are identical.

  • Other updates:

    • Running make check and make ptest takes much longer time to complete. This is because the testing mechanism has been revised to become more thorough than before.

  • Bug fixes

    • Fix problem of building PnetCDF shared library when using NVIDIA HPC compilers, nvc, nvc++, and nvfortran.
    • Fix data movement when new record variables are added to an existing file that does not change the starting offset of record variable section. See PR #199.

  • New I/O benchmarks

    • benchmarks/C/indep_data_obj_create.c - It evaluates the performance of creating a large number of data objects (dimensions and variables) in an output file. This benchmark is used in a paper published in the PDSW Workshop of SC 2025. DOI: 10.1145/3731599.3767512

  • New test programs

    • test/testcases/tst_grow_data.c -- It tests the case when adding new variables by re-entering the define mode multiple time without causing the file header extent to grow. It also tests a case when adding a new record variable that does not change the starting offset of the record variable section in the file.