--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Sphinx/source/faq/scalability.rst	Thu Jan 31 18:41:44 2019 +0100
@@ -0,0 +1,60 @@
+.. _scalability:
+
+Scalability of Orthanc
+======================
+
+One of the most common question about Orthanc is: *"How many DICOM
+instances can be stored by Orthanc?"* 
+
+The source code of Orthanc imposes no such hard limit by itself. The
+stress is actually put on the underlying database engine, and on the
+storage area (check out :ref:`orthanc-storage`). As explained in the
+:ref:`troubleshooting section <troubleshooting>`, the built-in SQLite
+database engine should be replaced by an enterprise-ready database
+engine as soon as the number of DICOM instances grow above about
+50,000 (check out the :ref:`postgresql` and :ref:`mysql`). It is also
+true that the performance of Orthanc in the presence of large
+databases has continuously improved over time, especially when it comes
+to the speed of :ref:`DICOM C-FIND <dicom-find>`.
+
+Here is a generic setup that should provide best performance in the
+presence of large databases:
+
+* Make sure that :ref:`run-time debug assertions <troubleshooting>`
+  are turned off. A warning will show in the logs if this is not the
+  case.
+
+* Make sure to use the latest release of Orthanc (1.5.3 at the time of
+  writing).
+
+* We suggest to use the latest release of the :ref:`PostgreSQL plugin
+  <postgresql>` to store the database index (3.0 at the time of
+  writing). Make sure that ``EnableIndex`` is set to ``true``.
+
+* We suggest to use the default filesystem storage area. Of course,
+  make sure that the filesystem is properly backup, and that
+  technologies such as RAID are enabled. Make sure that the option
+  ``EnableStorage`` of the PostgreSQL plugins is set to ``false``.
+
+* Obviously, the PostgreSQL database should be stored on a high-speed
+  drive (SSD). This is less important for the storage area.
+
+* The :ref:`Orthanc configuration file <configuration>` should have
+  the following values for performance-related options (but make sure
+  to understand their implication):
+  
+  * ``StorageCompression = false``
+  * ``LimitFindResults = 100``
+  * ``LimitFindInstances = 100``
+  * ``KeepAlive = true``
+  * ``TcpNoDelay = true``
+  * ``SaveJobs = false``
+  * ``StorageAccessOnFind = Never``
+
+* Make sure to carefully :ref:`read the logs <log>` in ``--verbose``
+  mode, especially at the startup of Orthanc. The logs may contain
+  very important information regarding performance.
+
+* Make sure to read guides about the :ref:`tuning of PostgreSQL
+  <https://wiki.postgresql.org/wiki/Performance_Optimization>`__.
+