zstan commented on code in PR #13685:
URL: https://github.com/apache/ignite/pull/13685#discussion_r4416089329
##########
docs/_docs/SQL/sql-calcite.adoc:
##########
@@ -1294,3 +1309,76 @@ If neither option is specified, Ignite uses the
transaction timeout.
`SELECT ... FOR UPDATE` is supported only for plain `SELECT` queries over
cache-based tables and joins of such tables.
It is not supported for `DISTINCT`, `GROUP BY`, `HAVING`, aggregate-only
result sets, system views, or table functions.
====
+
+== Legacy H2 Engine [[legacy-h2-engine]]
+
+The SQL engine based on the H2 database is provided by the `ignite-indexing`
module. The module is shipped in the `libs` folder of the binary distribution
next to `ignite-calcite`, so a node started with the `ignite.{sh|bat}` script
has both engines: the Calcite-based engine is the default one and the H2 engine
is available by name, see <<Configuring Query Engines>>. If you start Ignite
from your application and manage its dependencies with Maven, add the
`ignite-indexing` dependency to get the H2 engine.
+
+To make the H2 engine the default engine again, configure it explicitly with
`IndexingQueryEngineConfiguration.setDefault(true)`, as shown in <<Configuring
Query Engines>>. This is the simplest way to keep the previous behaviour after
an upgrade.
+
+[WARNING]
+====
+Every node of the cluster, including thick client nodes and the nodes embedded
into an application, must have the same set of engine modules as the server
nodes.
+====
+
+=== Features Implemented by the H2 Engine Only
+
+The following features work only when the query is executed by the H2 engine:
the `ignite-indexing` module must be on the classpath of every node, and the H2
engine must be selected for the query or the connection, or configured as the
default engine.
+
+* The link:sql-reference/operational-commands#copy[COPY] and
link:sql-reference/operational-commands#set-streaming[SET STREAMING] commands
and the streaming modes of the JDBC and ODBC drivers.
+* link:SQL/JDBC/jdbc-driver#partition-awareness[Partition awareness] of the
JDBC thin driver. The Calcite-based engine does not return the partition
information to the driver, so the driver sends the queries of such a connection
to a random node of the cluster.
+* The `USE INDEX` syntax. The Calcite-based engine provides the `FORCE_INDEX`
and `NO_INDEX` <<hints,hints>>.
Review Comment:
do we need an examples here? or it\`s just a description and examples is not
expected here ?
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