[netcdf-java] Opening a GridDataset for large NcML aggregations

[Jon Blower]

Hi John,

It's a JoinNew, because the data files do not contain a time axis.
Hence we use a <scan> element and the time axis values are deduced
from the file names using dateFormatMark.  Our ncml file is attached.

Yes, this is in our own application (ncWMS) not the TDS.

Cheers, Jon

On Tue, Mar 18, 2008 at 2:21 AM, John Caron <caron at unidata.ucar.edu> wrote:
> HiJon:
>
>  Are these JoinExisting or JoinNew ? How is the coordinate value specified? You are doing this in your own application, not in TDS?
>
>
>  Jon Blower wrote:
>  > Hi all,
>  >
>  > Using the Java NetCDF libraries, version 2.2.22, we have notice that
>  > opening a GridDataset using TypedDatasetFactory.open() is slow when
>  > the dataset in question is an NcML aggregation over a long timeseries
>  > (around a thousand timesteps, with one timestep per file).  The call
>  > to TDF.open() takes around 3 seconds every time, which is a problem
>  > for our application, where performance is important.
>  >
>  > We are using the NetcdfDatasetCache, which doesn't seem to help with
>  > this problem.  Is there something we can do to speed up the process of
>  > creating a GridDataset?  I don't think this was a problem for us in
>  > previous library versions, where we used a different syntax
>  > ("GridDataset gd = new GridDataset(nc);").
>  >
>  > I guess we could cache the GridDataset object in memory at the
>  > application level, but is there a reason not to do this (e.g. if this
>  > is a very large object)?
>  >
>  > Here's what we do using version 2.2.22:
>  >
>  >    NetcdfDataset nc = NetcdfDataset nc = NetcdfDatasetCache.acquire(filename);
>  >    GridDataset gd =
>  > (GridDataset)TypedDatasetFactory.open(DataType.GRID, nc, null, null);
>  >
>  > Thanks, Jon
>  >
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