Avoid read docs twice when filtered `_changes` is triggered

[jiahuili430]

Overview

• When filered _changes is triggered, open_revs() will read docs. If request parameter has include_docs=true, then doc_member() will also read docs.

Change filter/3 to filter/5 to avoid the above behavior.

• When using filtered _changes with style=all_docs, conflicts=true and include_docs=true, the response should contain the _conflicts field.

Add open_all_revs_include_doc/2 to include this field.

• Add tests to verify the number of calls to open_doc/3.

Testing recommendations

make eunit apps=chttpd suites=chttpd_changes_test
make eunit apps=couch suites=couch_changes_tests

Related Issues or Pull Requests

Checklist

• [ ] Code is written and works correctly
• [x] Changes are covered by tests
• [ ] Any new configurable parameters are documented in rel/overlay/etc/default.ini
• [ ] Documentation changes were made in the src/docs folder
• [ ] Documentation changes were backported (separated PR) to affected branches

[rnewson]

When filered _changes is triggered, open_rev() will increment stats. If query has include_docs=true, then doc_member() will also increase stats.

In that code path it sounds like the document is being read twice, so incrementing database_reads twice sounds correct. Of course if we could avoid the second read that would be great.

Did I misunderstand the problem?

[jiahuili430]

In that code path it sounds like the document is being read twice, so incrementing database_reads twice sounds correct. Of course if we could avoid the second read that would be great.

I'll try to avoid the second read, thanks for the review.

[nickva]

To reduce the size of the PR, wonder if it would make sense to extract the enhanced tests into a separate PR. We don't intend to change the behavior of _changes endpoint to tests could be updated first then optimize the doc loading separately.

[jiahuili430]

To reduce the size of the PR, wonder if it would make sense to extract the enhanced tests into a separate PR. We don't intend to change the behavior of _changes endpoint to tests could be updated first then optimize the doc loading separately.

Sure, dropped the first commit.

[jiahuili430]

Thanks for the script, @nickva. I'll investigate more.