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VFD SWMR Punch List
This document lives at [https://bitbucket.hdfgroup.org/users/dyoung/repos/vchoi_fork/browse/doc/VFD_SWMR_Punch_List.md?at=refs%2Fheads%2Ffeature%2Fvfd_swmr](https://bitbucket.hdfgroup.org/users/dyoung/repos/vchoi_fork/browse/doc/VFD_SWMR_Punch_List.md?at=refs%2Fheads%2Ffeature%2Fvfd_swmr)
19 November 2019
1. Design optimizations in index writes. Perhaps write deltas only,
with a full index every n ticks?
2. Design work for NFS and object store versions.
3. Design work for journaling variation.
4. **Vailin, complete** Add support for opening multiple files in either VFD SWMR writer or
VFD SWMR writer mode. See addition of the EOT queue in section 3.2.2
of the RFC, and related changes in sections 3.3 and 3.3.2.
5. **Vailin, complete**Add the pb\_expansion\_threshold field to the
H5F\_vfd\_swmr\_config\_t structure, and update
H5Pset\_vfd\_swmr\_config()and
H5Pget\_vfd\_swmr\_config()accordingly.
6. **Vailin, in progress**Implement end tick now API call. See section 3.1.2 of the RFC for
specifications.
7. **Vailin, in progress**Implement enable / disable EOT call. See section 3.1.3 of the RFC
for specifications.
8. Implement option to flush raw data as part of EOT -- write
performance test to characterize the performance hit.
9. **Vailin, complete** Move VFD SWMR specific H5F code to its own file -- say
H5Fvfd\_swmr.c.
10. Update the new page buffer to support the pb\_expansion\_threshold,
and trigger an early end of tick if the threshold is exceeded.
11. Modify metadata file write call to allow the location of the index
to float and thus be of arbitrary size.
12. Add code to remove entries from the index after they have been
written to the HDF5 file, and have not been modified for at least
max\_lag ticks.
13. Tidy short cuts in the initial implementation. These include:
- **Vailin complete**Odd behavior in the superblock refresh routine (see comments in
code). Figure out what is going on, and then either bypass the
issue or fix it as seems appropriate.
- **Vailin complete**Comment H5F\_vfd\_swmr\_config\_t in H5Fpublic.h properly.
- Cleanup EOA hack in H5FD\_read().
- Address file open failures in SWMR tests. These appear to be
cases in which the writer finishes before the reader opens --
causing the reader to fail as the metadata file no longer
exists. If so, handle this more gracefully.
14. Add support for specifying the VFD that sits under the VFD SWMR
reader VFD. Probably do this as part of the pluggable VFD design
that Jake is working on.
15. Modify the metadata cache so that we don't allocate space for the
page hash table unless the file is opened in VFD SWMR reader mode.
16. Implement the logging facility (section 3.14 RFC)
17. Test code to expose existing page buffer bugs and fix same. Note
that they seem to appear primarily on Jelly.
- DLL pre remove sanity check assertion failure
- vfd\_swmr\_addrem\_writer: H5PB.c:2981:
H5PB\_\_mark\_entry\_dirty: Assertion
'(entry\_ptr)-\>delay\_write\_until \> (pb\_ptr)-\>cur\_tick'
failed.
18. Flesh out designs for unit, integration and performance tests suites
as outlined in the RFC. Implement same.
19. **David, needs merge** Fix memory leak in sparse-reader test.
David found that the shadow index was leaked by VFD SWMR readers
and plugged the leak. Now the sparse reader tests do not use up
all of the memory on `jelly`. David fixed the bug on his branch
`vfd_swmr-merge-attempt-2`, which as of 19 Nov 2019 has not been
merged to `feature/vfd_swmr`.
20. **David, needs merge** Test John's patch that repairs the superblock flags
mismatch that crashes the reader.
David found that the patch fixed the demo crashes. He applied the
patch to his branch `vfd_swmr-merge-attempt-2`, which has not yet
been merged to `feature/vfd_swmr` as of 19 Nov 2019.
21. Investigate a potential time-of-check, time-of-use race condition
involving EOA/EOF and the skip\_read variable in some of the H5PB
routines.
22. Understand use of H5F\_t on branch feature/vfd\_swmr instead of
H5C\_t as on develop branch.
23. *Temporarily* reserve a new superblock flag for VFD SWMR for
development purposes.
24. Prior to feature merge, *permanently* reserve a new superblock flag.
25. Revisit the global heap. The global heap receives data types (a form
of metadata) and variable-length (VL) data such as strings. It is
translated to raw data on its way down the HDF5 software stack. If
the global heap is modified/replaced as currently planned, then VFD
SWMR does not have to deal with it. However, if the global heap
overhaul does not take place, then we have more work to do.
26. **David, in-progress** Fix the expand/shrink test.
The test *probably* fails because the dataset extent is enlarged
before the data is written, so arbitrary data is present until the
data appears. If a tick sneaks in between the `H5Dset_extent` and
the `H5Dwrite`, then the reader may read the arbitrary data.
In the `gaussian` test, I have a heuristic that avoids reading
arbitrary data. I may replicate that in the expand/shrink test.
Ultimately, we should suspend ticks over the H5Dset_extent/H5Dwrite.
27. **Vailin, complete** Change the field name "vfd_swmr_writer" to "writer" in
"struct H5F_vfd_swmr_config_t" and all references to it. See page 11 in the RFC.
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