This allows changing the internals of TRI_vector_t structs in order to make the struct smaller.
On 64 bits, the size of TRI_vector_t is reduced from 48 bytes to 28 bytes.
TRI_json_t does benefit from this, as its biggest component is a TRI_vector_t.
This patch reduces collection loading time by preallocating enough space in primary index ahead of time.
When a collection is closed, the number of documents in the collection will be stored in the collection's JSON info file.
This value is used to determine the initial size for the primary index when the collection is loaded next time.
Datafile iteration has also been made slightly faster.
The above changes will have a significant benefit when the collection's datafiles are already in the OS buffer cache, and when there are no secondary indexes.
Loading datafiles from disk or building secondary indexes may be more time-consuming than the improvements reapable by this patch, but the patch shouldn't hurt anyway.
Locking is now done in an extra round after the query is fully
instanciated in the cluster. All participating shards are locked
in alphabetical order of their shard ID (local collection name).
For this to work there is a new action in the RestAqlHandler plus a
mechanism to prevent the usual locking from happening: Each thread has a
thread local static class variable of
triagens::arango::Transaction::_makeNolockHeaders
which is of type std::unordered_set<std::string>*.
Whenever this is not equal to nullptr and a local collection name is
stored in there, no locking or unlocking takes place. This information
is forwarded by the X-Arango-Nolock HTTP header, whenever an HTTP
request is sent via ClusterComm to a shard.