Retry filter_docs sequentially if the patch exceeds couchjs stack

[rnewson]

Overview

A document with lots of conflicts can blow up couchjs if the user
calls _changes with a javascript filter and with style=all_docs as
this option causes up to fetch all the conflicts.

All leaf revisions of the document are then passed in a single call to
ddoc_prompt, which can fail if there's a lot of them.

In that event, we simply try them sequentially and assemble the
response from each call.

Testing recommendations

Covered by unit test, but manual test as follows;

You need to create a highly conflicted document and lower couchjs's memory allowance for a practical test. Here's how I did it;

1. edit dev/run;

-    qs_javascript = toposixpath("%s %s" % (couchjs, mainjs))
+    qs_javascript = toposixpath("%s -S 1048576 %s" % (couchjs, mainjs))

2. create a filter;

curl 'foo:bar@localhost:15984/db1/_design/foo' -XPUT -d '{"filters":{"pass":"function(doc,req) { log(JSON.stringify(doc)); return true; }"}}'

3. create a highly conflicted doc;

for I in {1..2000}; do curl 'foo:bar@localhost:15984/db1/bigdoc?new_edits=false' -XPUT -d "{\"_rev\":\"1-conflict$I\", \"foo\":\"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"}" ; done

4. then run it through filter_docs;

curl 'foo:bar@localhost:15984/db1/_changes?filter=foo/pass&style=all_docs'

Without the patch, this will fail with an {exit_status, 1} error from couchjs. With it, it succeeds.

Related Issues or Pull Requests

#3248

Checklist

• Code is written and works correctly
• Changes are covered by tests
• Any new configurable parameters are documented in rel/overlay/etc/default.ini
• A PR for documentation changes has been made in https://github.com/apache/couchdb-documentation

[davisp]

+1