Nick North created COUCHDB-1495:
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Summary: Allow the UUID algorithm to vary by database
Key: COUCHDB-1495
URL: https://issues.apache.org/jira/browse/COUCHDB-1495
Project: CouchDB
Issue Type: Improvement
Components: Database Core
Affects Versions: 1.2
Reporter: Nick North
Priority: Minor
The UUID algorithm for generating document ids is currently a global setting,
affecting all databases. When returning to
https://issues.apache.org/jira/browse/COUCHDB-1373 after a long hiatus, I
realised it might be useful to allow a default algorithm, with per-database
overrides.
I propose that the uuids section of the config be of the following form,
modelled somewhat on the compactions section:
algorithm = AlgorithmName
overrides = [ {DatabaseName, AlgorithmName, [ { ParamName, ParamValue},
{ParamName, ParamValue}, ...]},
{DatabaseName, AlgorithmName, [ { ParamName, ParamValue},
{ParamName, ParamValue}, ...]}, ...]
The "algorithm" element is exactly as it now is, specifying the default UUID
algorithm, to be used when the algorithm is not overridden and for responding
to the _uuids HTTP request. It also gives backwards compatibility.
The optional "overrides" element specifies algorithms for named databases, each
with a list of algorithm-specific parameters. The list may be empty (or
potentially absent altogether, which would have the same meaning as an empty
list).
The special database name _default is used to specify a default algorithm that
needs parameters or instead or the "algorithm" element.
Implementation would be by giving the couch_uuids gen_server a state consisting
of a dictionary mapping database names to an {AlgorithmName, AlgorithmState}
pair, where AlgorithmState is an algorithm-dependent value and the default
algorithm is associated with database name _default. Requests for a UUID for a
specific database would pass in the database name for use in determining the
right algorithm. [This gives rise to a potential objection to the proposal, as
there is a performance hit: every new document id requires a dictionary lookup
of the database name, and possibly a second lookup of the _default entry if the
name is not found; there may also be a dictionary insertion of the new
AlgorithmState value. However, I suggest that is small compared to everything
else that goes on when creating a document.]
If people like this idea, I am happy to put forward some code, and wrap in the
implementation of https://issues.apache.org/jira/browse/COUCHDB-1373, which I
have neglected for far too long. The two proposals are not necessarily tied
together, but implementing this one changes the implementation of the other so
it is more convenient to do both together.
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