(In reply to comment #1)
> Implemented for EDS contacts and adding/updating.

However, it turned out to be faulty when used for something other than simple
PBAP caching and therefore is only used for that in SyncEvolution 1.4.

See
commit c435e937cd406e904c437eec51a32a6ec6163102
Author: Patrick Ohly <patrick.ohly@intel.com>
Date:   Fri Nov 29 14:02:05 2013 +0100

    engine: disable batching by default

    Change the EDS backend to not batch by default and only enable it
    for PIM Manager PBAP syncs.

    This avoids unnecessary overhead when running a normal SyncML sync
    with a non-SyncEvolution peer, because then the batched operation
    would be flushed immediately by the Synthesis engine, and more
    importantly, it fixes a segfault in
    Client::Sync::eds_event_eds_contact::testLargeObject EDS<->DAV tests.

    Enabling batching during general syncs obviously needs further work...