Horton

Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Erik Rijkers <er@xs4all.nl>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-08-19T04:40:43Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Tighten the concurrent abort check during decoding.

  2. Improve hash_create()'s API for some added robustness.

  3. Use HASH_BLOBS for xidhash.

  4. Fix initialization of RelationSyncEntry for streaming transactions.

  5. Remove unused function declaration in logicalproto.h.

  6. Add additional tests to test streaming of in-progress transactions.

  7. Fix inline marking introduced in commit 464824323e.

  8. Add support for streaming to built-in logical replication.

  9. Fix the SharedFileSetUnregister API.

  10. Fix comment in procarray.c

  11. Suppress compiler warning in non-cassert builds.

  12. Extend the BufFile interface.

  13. Mark a few logical decoding related variables with PGDLLIMPORT.

  14. Implement streaming mode in ReorderBuffer.

  15. Extend the logical decoding output plugin API with stream methods.

  16. WAL Log invalidations at command end with wal_level=logical.

  17. Immediately WAL-log subtransaction and top-level XID association.

  18. Allow logical replication to transfer data in binary format.

  19. Only superuser can set sslcert/sslkey in postgres_fdw user mappings

  20. Track statistics for spilling of changes from ReorderBuffer.

  21. Add logical_decoding_work_mem to limit ReorderBuffer memory usage.

  22. logical decoding: process ASSIGNMENT during snapshot build

  23. Emit invalidations to standby for transactions without xid.

On Mon, Aug 17, 2020 at 6:29 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
>
> In last patch v49-0001, there is one issue,  Basically, I have called
> BufFileFlush in all the cases.  But, ideally, we can not call this if
> the underlying files are deleted/truncated because those files/blocks
> might not exist now.  So I think if the truncate position is within
> the same buffer we just need to adjust the buffer,  otherwise we just
> need to set the currFile and currOffset to the absolute number and set
> the pos and nbytes 0.  Attached patch fixes this issue.
>

Few comments on the latest patch v50-0001-Extend-the-BufFile-interface
1.
+
+ /*
+ * If the truncate point is within existing buffer then we can just
+ * adjust pos-within-buffer, without flushing buffer.  Otherwise,
+ * we don't need to do anything because we have already deleted/truncated
+ * the underlying files.
+ */
+ if (curFile == file->curFile &&
+ curOffset >= file->curOffset &&
+ curOffset <= file->curOffset + file->nbytes)
+ {
+ file->pos = (int) (curOffset - file->curOffset);
+ return;
+ }

I think in this case you have set the position correctly but what
about file->nbytes? In BufFileSeek, it was okay not to update 'nbytes'
because the contents of the buffer are still valid but I don't think
the same is true here.

2.
+ int curFile = file->curFile;
+ off_t curOffset = file->curOffset;

I find the previous naming (newFile, newOffset) was better as it
distinguishes them from BufFile variables.

3.
+void
+SharedFileSetUnregister(SharedFileSet *input_fileset)
+{
..
+ /* Delete all files in the set */
+ SharedFileSetDeleteAll(input_fileset);
..
}

I am not sure if this is completely correct because we call this
function (SharedFileSetUnregister) from BufFileDeleteShared which
would have already removed all the required files. This raises the
question in my mind whether it is correct to call
SharedFileSetUnregister from BufFileDeleteShared from the API
perspective as one might not want to remove the entire fileset at that
point of time. It will work for your use case (where while removing
buffile you also want to remove the entire fileset) but not sure if it
is generic enough. For your case, I wonder if we can directly call
SharedFileSetDeleteAll and we can have a call like
SharedFileSetUnregister which will be called from it.

-- 
With Regards,
Amit Kapila.