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From "Adam Kocoloski (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COUCHDB-1132) Track used space of database and view index files
Date Tue, 19 Apr 2011 18:58:05 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-1132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13021728#comment-13021728
] 

Adam Kocoloski commented on COUCHDB-1132:
-----------------------------------------

Thanks Filipe.  I've only gotten a chance to look briefly at your work, but it seems very
cleanly structured and well-organized.  It looks like your implementation is going to be a
bit more efficient because it doesn't require an additional term_to_binary call on document
updates.  It also has the nice property that data_size ~= disk_size after compaction.

You're right that the work Bob and I did only included "user data" in the size computation.
 It intentionally excludes all of the indexes, MD5s, etc. that are needed for proper operation
of CouchDB but cannot be controlled by the user.

We did set the size of old documents and KV pairs to zero rather than reporting a null data_size
pre-compaction.

> Track used space of database and view index files
> -------------------------------------------------
>
>                 Key: COUCHDB-1132
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-1132
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: Database Core
>            Reporter: Filipe Manana
>             Fix For: 1.2
>
>
> Currently users have no reliable way to know if a database or view index compaction is
needed.
> Both me, Adam and Robert Dionne have been working on a feature to compute and expose
the current data size (in bytes) of databases and view indexes. These computations are exposed
as a single field in the database info and view index info URIs.
> Comparing this new value with the disk_size value (the total space in bytes used by the
database or view index file) would allow users to decide whether or not it's worth to trigger
a compaction.
> Adam and Robert's work can be found at:
> https://github.com/cloudant/bigcouch/compare/7d1adfa...a9410e6
> Mine can be found at:
> https://github.com/fdmanana/couchdb/compare/file_space
> After chatting with Adam on IRC, the main difference seems to be that they're work accounts
only for user data (document bodies + attachments), while mine also accounts for the btree
values (including all meta information, keys, rev trees, etc) and the data added by couch_file
(4 bytes length prefix, md5s, block boundary markers).
> An example:
> $ curl http://localhost:5984/btree_db/_design/test/_info
> {"name":"test","view_index":{"signature":"aba9f066ed7f042f63d245ce0c7d870e","language":"javascript","disk_size":274556,"data_size":270455,"updater_running":false,"compact_running":false,"waiting_commit":false,"waiting_clients":0,"update_seq":1004,"purge_seq":0}}
> $ curl http://localhost:5984/btree_db
> {"db_name":"btree_db","doc_count":1004,"doc_del_count":0,"update_seq":1004,"purge_seq":0,"compact_running":false,"disk_size":6197361,"data_size":6186460,"instance_start_time":"1303231080936421","disk_format_version":5,"committed_update_seq":1004}
> This example was executed just after compacting the test database and view index. The
new filed "data_size" has a value very close to the final file size.
> The only thing that my branch doesn't include in the data_size computation, for databases,
are the size of the last header, the size of the _security object and purged revs list - in
practice these are very small and insignificant that adding extra code to account them doesn't
seem worth it.
> I'm sure we can merge the best from both branches.
> Adam, Robert, thoughts?

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