Hi,
On 13 Apr 2009, at 06:36, sftf wrote:
I search the database for a small (but geographically distributed on
2-3 nodes)
CRM and would like to know the answers to several questions about
the couchdb.
1. What is the (read) performance of couchdb compared to the
relational database like PostgreSQL?
Is it usually faster?
Speed is not the issue.
CouchDB is not meant to be faster than any fine-tuned, mature
solution. It is designed to handle high levels of concurrency while
operating fault tolerant. At the expense of just being "fast
enough" (but not "faster"), you can serve more users all the time (not
saying this can't be done with Postgres or any other system).
CouchDB is also a lot simpler than an RDBMS. Less moving parts means
less bugs, fewer ways to screw up, fewer ways to screw up performance.
I'd wager a non-query-cached multi-table JOIN might end up being
slower than a document- or view-result read, but there are just too
many factors including the apples-and-oranges one, that this exercise
is futile.
In my experience, CouchDB is plenty fast. Certainly fast enough so
users won't notice a bunch of serial queries that build up a web page,
e.g.
2. What is on disk layout of couchdb (one big file or the many
little or something else) and
can we manage where to store various parts of the database in
filesystem?
CouchDB can host many databases. Each database lives in a single file
on the database. Views for a database live in a file each. There are
two .ini directives that let you specify locations for database- and
view-files. With symlinks, you are truly flexible.
3. Is the current version tolerant to power failures?
Yes.
4. Can replication be unidirectional?
This is the default case.
Can the replication carry out only a certain subset of the
documents, not whole database?
Yes and no. At the moment, you can't say "replicate only documents
where field A has value 'foo'". What you can do though, is write
validation functions on the target servers that reject writes where
documents have a field A that doesn't have the value 'foo'. This
doesn't save you sending all docs to all nodes, but nodes would only
ever accept the ones you want to be there. The other case will likely
show up in future versions of CouchDB.
5. What are the advantages/key differense of the couchdb compared
with the existing projects like MongoDB?
Ease of use, speed, simplicity: Pick two.
See Benoit's link for a more detailed answer :)
Cheers
Jan
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