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From Nick North <nort...@gmail.com>
Subject Replicated database size
Date Tue, 15 May 2012 12:55:09 GMT
I'm curious about the size of replicated CouchDb databases in comparison to
each other. I have four databases, each with pull replications from the
other three, but they report quite different data sizes. Two of them say:

{"db_name":"hydra","doc_count":1489060,"doc_del_count":2754893,"update_seq":6998882,"purge_seq":0,"compact_running":false,"disk_size":3213656193,"data_size":1395943755,"instance_start_time":"1337067567481841","disk_format_version":6,"committed_update_seq":6998882}

While the other two say this - note the difference in data_size:

{"db_name":"hydra","doc_count":1489441,"doc_del_count":2755302,"update_seq":4375865,"purge_seq":0,"compact_running":false,"disk_size":7599413027,"data_size":7265993199,"instance_start_time":"1337014746154865","disk_format_version":6,"committed_update_seq":4375865}

(There is some discrepancy in the doc_count because new documents are
being posted continuously, and some went in in between fetching stats
for the various instances.) Other possibly relevant information:


   - All the replications appear to be in working order so I don't
believe there is a backlog of documents waiting to be replicated.
   - The database has just one design view and whether or not it has
been queried does not seem to make any difference to whether the
database is "large" or "small".
   - Compaction makes little difference, in that the "large" instances
always remain much larger than the "small" ones.
   - Everything is running CouchDb 1.2 on Windows: the "small"
instances on Windows 7 and Windows Vista, and the "large" ones on
Windows Server 2008.
   - File_compression is set to "snappy" in all cases and there are no
attachments anywhere.

Can anyone suggest what might be going on here? My best guess is that
it's to do with file compression on Windows Server but that is a
guess, so I'm intending to do some experimentation with the other file
compression options. I'd be grateful for any thoughts, as I'm planning
out disk requirements for a system with ten times the capacity of the
current one, and would very much like to be do that with some
certainty about file sizes. Thanks in advance for any help,

Nick North

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