zstan commented on code in PR #13116:
URL: https://github.com/apache/ignite/pull/13116#discussion_r3208490543
##########
docs/_docs/SQL/sql-calcite.adoc:
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@@ -483,3 +427,54 @@ Disables certain optimizer rules. This is an optimizer
level hint.
----
SELECT /*+ DISABLE_RULE('MergeJoinConverter') */ T1.* FROM TBL1 T1 JOIN TBL2
T2 ON T1.V1=T2.V1 WHERE T2.V2=?
----
+
+== Transactions [[transactions]]
+
+Transactions on `READ_COMMITTED` isolation level are supported for SQL queries
in Calcite query engine.
+To ensure backward compatibility transactions support disabled, by default.
+To enable, please, configure like the following:
+
+[tabs]
+--
+tab:XML[]
+[source,xml]
+----
+<bean class="org.apache.ignite.configuration.IgniteConfiguration">
+ <property name="transactionConfiguration">
+ <bean class="org.apache.ignite.configuration.TransactionConfiguration">
+ <property name="txAwareQueriesEnabled" value="true" />
+ ...
+ </bean>
+ </property>
+ ...
+</bean>
+----
+--
+
+The following API "transactional aware":
+
+* key-value API.
+* SQL queries with Calcite engine.
+* Scan queries.
+
+"Transactional aware" means:
+
+1. ACID in the same way as key-value API.
+2. Any data changed or removed by the query will not be visible to the
concurrent query until transaction committed.
+3. Any data changed by the query will be returned updated by subsequent
queries of the same transaction.
+4. And data removed by the query will not be returned by subsequent queries of
the same transaction.
+
+So, when `txAwareQueriesEnabled = true` you can:
+
+* Perform INSERT, UPDATE, DELETE statements with regular transaction
guarantees.
+* Mix key-value, SQL and Scan queries to process same dataset.
+
+
+[NOTE]
+====
+[discrete]
+=== SELECT ... FOR UPDATE
+Currently, no locks are held by the UPDATE or SELECT statements.
+`SELECT ... FOR UPDATE` statement not supported.
Review Comment:
Let`s describe syntax like :
`update t set val = val + 1 WHERE id = 1`
what does it means : Currently, no locks are held by the UPDATE or SELECT
lets mean:
For example, if you execute a query like `SET salary = salary + 50 WHERE id
= 1` concurrently across multiple threads, note that due to the lost-update
anomaly, the final value may not equal the original salary plus 50 multiplied
by the number of threads.
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