Fixes gh-1054 _session_settings system space

Author: pgulutzan

doc/book/box/box_space.rst

@@ -162,7 +162,10 @@ Below is a list of all ``box.space`` functions and members.
     | :ref:`box.space._vcollation                  | (Metadata) List of collations   |
     | <box_space-vcollation>`                      | accessible for the current user |
     +----------------------------------------------+---------------------------------+
-
+    | :ref:`box.space._session_settings            | (Metadata) List of settings     |
+    | <box_space-session_settings>`                | affecting behavior of the       |
+    |                                              | current session                 |
+    +----------------------------------------------+---------------------------------+
 
 .. module:: box.space
 
@@ -2716,6 +2719,33 @@ organizing:
     of its tuples is identical to that of :ref:`box.space._collation <box_space-collation>`, but
     permissions for certain tuples are limited in accordance with user privileges.
 
+.. _box_space-session_settings:
+
+.. data:: _session_settings
+
+    ``_session_settings`` is a temporary system space with a list of settings that
+    may affect behavior, particularly SQL behavior, for the current session.
+    It uses a special engine named 'service'.
+    Every 'service' tuple is created on the fly, that is, new tuples are made every time ``_session_settings`` is accessed.
+    Every settings tuple has two fields: ``name`` (the primary key) and ``value``.
+    The tuples' names and default values are: |br|
+    ``sql_default_engine``: default :ref:`storage engine <engines-chapter>` for new SQL tables. Default = 'memtx'. |br|
+    ``sql_defer_foreign_keys``: whether foreign-key checks can wait till commit. Default = false. |br|
+    ``sql_full_column_names``: no effect at this time. Default = false. |br|
+    ``sql_full_metadata``: whether SQL result metadata will have more than just name and type. Default = false. |br|
+    ``sql_parser_debug``: whether to show parser steps for following statements. Default = false. |br|
+    ``sql_recursive_triggers``: whether a triggered statement can activate a :ref:`trigger <sql_create_trigger>`. Default = true. |br|
+    ``sql_reverse_unordered_selects``: whether result rows are usually in reverse order if there is no :ref:`ORDER BY clause <sql_order_by>`. Default = false. |br|
+    ``sql_select_debug``: whether to show execution steps during :ref:`SELECT <sql_select>`. Default = false. |br|
+    ``sql_vdbe_debug``: for use by Tarantool's developers. Default = false. |br|
+    Three requests are possible: :ref:`select <box_space-select>` and :ref:`get <box_space-get>` and :ref:`update <box_space-update>`.
+    For example, after ``s = box.space._session_settings``,
+    ``s:select('sql_default_engine')`` probably returns ``{'sql_default_engine', 'memtx'}``, and
+    ``s:update('sql_default_engine', {{'=', 'value', 'vinyl'}})`` changes the default engine to 'vinyl'. |br|
+    Updating ``sql_parser_debug`` or ``sql_select_debug`` or ``sql_vdbe_debug`` has no effect unless
+    Tarantool was built with -DCMAKE_BUILD_TYPE=Debug. To check if this is so, look at
+    ``require('tarantool').build.target``.
+
 .. _box_space-operations-detailed-examples:
 
 ===============================================================================