# SWMR - extend dataset by 1000 records and write records one by one

**URL:** <https://forum.hdfgroup.org/t/swmr-extend-dataset-by-1000-records-and-write-records-one-by-one/5363>\
**Category:** HDF5 Library\
**Created:** [February 5, 2019, 11:02am UTC](https://forum.hdfgroup.org/t/swmr-extend-dataset-by-1000-records-and-write-records-one-by-one/5363 "2019-02-05T11:02:00Z")\
**Posts on this page:** 1\
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**Author:** ![paramon](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/p/8491ac/32.png) [@paramon](https://forum.hdfgroup.org/u/paramon)\
**Post date:** [February 5, 2019, 1:02pm UTC](https://forum.hdfgroup.org/t/swmr-extend-dataset-by-1000-records-and-write-records-one-by-one/5363/4 "2019-02-05T13:02:10Z")

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Hi Maoz!

Extending by one record is no way currently, but might it be that the bug is fixed someday  
(or at least, enters JIRA)?

> [@\[BUG\] Compression doesn't compress data on SWMR](https://forum.hdfgroup.org/t/bug-compression-doesnt-compress-data-on-swmr/5280):
>
> Hello! To reproduce: Build and run attached [test980.c](https://hdf-discourse-1.s3.amazonaws.com/original/2X/d/d0e3c52264470ae2f2e33e99b68092cb1c75417c.c) (1.4 KB) Observe the size of test.h5 is 5,705 bytes (correct). Uncomment H5Fstart\_swmr\_write(file); rebuild and run. Now the file size exploded to 1,913,763 bytes! Originally reported in in [Compression doesn't compress data on SWMR · Issue #980 · h5py/h5py · GitHub](https://github.com/h5py/h5py/issues/980) (see more complete example there for motivation behind H5Fflushing repeatedly). Best wishes, Andrey Paramonov

Best wishes,  
Andrey Paramonov

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