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From "Filipe Manana (JIRA)" <>
Subject [jira] Commented: (COUCHDB-639) Make replication profit of attachment compression and improve push replication for large attachments
Date Fri, 19 Feb 2010 17:04:27 GMT


Filipe Manana commented on COUCHDB-639:

Hi Chris,

That is in fact the part I don't like, exposing the _bulk_doc_rep. I did it because when using
the doc multipart streamer, we can't use the same http body to include other docs (at least
not as far as I know). So _bulk_docs would be no longer _bulk_docs but _bulk_doc (singular).

The alternative I see, is to add a case clause in _bulk_docs, like:

case HttpHeaderContentType of
"multipart/related" ->
   % do the stuff of _bulk_doc_rep (new_edits is false, call update_docs with "replicated_changes")
_Else ->
   % ....

This probably, looks better?

It should copy new and old attachments (doesn't matter if they're compressed or not). Hummm,
what is there suspicious about that?


> Make replication profit of attachment compression and improve push replication for large
> ----------------------------------------------------------------------------------------------------
>                 Key: COUCHDB-639
>                 URL:
>             Project: CouchDB
>          Issue Type: Improvement
>          Components: Replication
>    Affects Versions: 0.11
>         Environment: trunk
>            Reporter: Filipe Manana
>         Attachments: rep-att-comp-and-multipart-trunk.patch
> At the moment, for compressed attachments, the replication uncompresses and then compresses
again the attachments. Therefore, a waste of CPU time.
> The push replication is also not reliable for very large attachments (500mb + for example).
Currently it sends the attachments in-lined in the respective JSON doc. Not only this requires
too much ram memory, it also wastes too much CPU time doing the base64 encoding of the attachment
(and also a decompression if the attachment is compressed).
> The following patch (rep-att-comp-and-multipart-trunk*.patch) addresses both issues.
Docs containing attachments are now streamed to the target remote DB using the multipart doc
streaming feature provided by couch_doc.erl, and compressed attachments are not uncompressed
and re-compressed during the replication
> JavaScript tests included.
> Previously doing a replication of a DB containing 2 docs with attachments of 100mb and
500mb caused the Erlang VM to consume near 1.2GB of ram memory in my system. With that patch
applied, it uses about 130Mb of ram memory.

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