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From "Filipe Manana (JIRA)" <j...@apache.org>
Subject [jira] Updated: (COUCHDB-639) Make replication profit of attachment compression and improve push replication for large attachments
Date Wed, 10 Feb 2010 23:42:33 GMT

     [ https://issues.apache.org/jira/browse/COUCHDB-639?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Filipe Manana updated COUCHDB-639:
----------------------------------

    Description: 
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.



  was:
Currently, when doing a pull replication where there are docs at the source DB with compressed
attachments:

1) The source decompresses the attachment before sending it to the target DB
2) The target compresses the attachment before storing it

Clearly, a waste of CPU, bandwidth and disk IO.

The following patch fixes the issue. JavaScript test included.

        Summary: Make replication profit of attachment compression and improve push replication
for large attachments  (was: Pull replication should profit of compressed attachments for
higher performance)

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.



> Make replication profit of attachment compression and improve push replication for large
attachments
> ----------------------------------------------------------------------------------------------------
>
>                 Key: COUCHDB-639
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-639
>             Project: CouchDB
>          Issue Type: Improvement
>          Components: Replication
>    Affects Versions: 0.11
>         Environment: trunk
>            Reporter: Filipe Manana
>         Attachments: pull-rep-att-comp-2.patch, pull-rep-att-comp.patch, 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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