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From "Chris Anderson (JIRA)" <>
Subject [jira] Commented: (COUCHDB-639) Make replication profit of attachment compression and improve push replication for large attachments
Date Fri, 19 Feb 2010 15:38:28 GMT


Chris Anderson commented on COUCHDB-639:

This patch applies cleanly and the tests are passing. I'm also +1 on the feature (and I sure
wouldn't mind committing this before 0.11 is tarballed as the code changes are enough that
it might make backporting fixes to 0.11 a pain later on.)

However, I'm not 100% sure about _bulk_docs_rep.

I'm concerned about having a separate endpoint designed for replication (gives the wrong idea
to people -- that replication is special. Replication is just another HTTP client.)

I'm also concerned about the implementation (does this copy only new attachments, or does
it copy all attachments?) I'd like it of Adam or someone else familiar with the replicator
could review this patch. (And apply it if you think it is right.)

> 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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