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Improve the documentation of _create with respect to shardKeys.

This commit is contained in:
Max Neunhoeffer 2014-04-04 17:13:49 +02:00
parent 78f72f76ad
commit d3df2a16e9
1 changed files with 14 additions and 0 deletions
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14
arangod/V8Server/v8-vocbase.cpp
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@ -8723,6 +8723,20 @@ static v8::Handle<v8::Value> JS_CompletionsVocbase (v8::Arguments const& argv) {
/// be changed once set.
/// This option is meaningless in a single server setup.
///
/// When choosing the shard keys, one must be aware of the following
/// rules and limitations: In a sharded collection with more than
/// one shard it is not possible to set up a unique constraint on
/// an attribute that is not the one and only shard key given in
/// `shardKeys`. This is because enforcing a unique constraint
/// would otherwise make a global index necessary or need extensive
/// communication for every single write operation. Furthermore, if
/// `_key` is not the one and only shard key, then it is not possible
/// to set the `_key` attribute when inserting a document, provided
/// the collection has more than one shard. Again, this is because
/// the database has to enforce the unique constraint on the `_key`
/// attribute and this can only be done efficiently if this is the
/// only shard key by delegating to the individual shards.
///
/// @EXAMPLES
///
/// With defaults: