[jira] [Resolved] (IGNITE-7604) SQL TX: Allow DML operations with reducer

["Sergey Kalashnikov (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IGNITE-7604?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sergey Kalashnikov resolved IGNITE-7604.
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    Resolution: Fixed

> SQL TX: Allow DML operations with reducer
> -----------------------------------------
>
>                 Key: IGNITE-7604
>                 URL: https://issues.apache.org/jira/browse/IGNITE-7604
>             Project: Ignite
>          Issue Type: Task
>          Components: sql
>            Reporter: Igor Seliverstov
>            Assignee: Sergey Kalashnikov
>            Priority: Major
>
> The following protocol is proposed for DML request with non-trivial reduce step within a transaction.
> 1. The SQL select part is deduced from a DML request and is split to form two-step map/reduce request.
> 2. Map query requests are sent to data nodes which execute them locally.
> 3. Resulting data pages are sent to originating node (reducer), which accumulates them.
> 4. Originating node performs reduce step on data received from map nodes and 
> forms batches of updates to apply to target table.
> 5. Lock requests containing delta updates are mapped and sent to data nodes storing the corresponding keys.
> 6. Lock acks are received at originating node and accumulated there, producing the total update counter.
> Note that no locks are acquired when map requests are processed. 
> This is consistent with what Oracle and PostgreSQL do (but not MySQL!) with respect to locks within complex DML statements.
> The Oracle docs (https://docs.oracle.com/cd/B28359_01/server.111/b28318/consist.htm#CNCPT1351) specifically states:
> The transaction that contains a DML statement does not need to acquire row locks on any rows selected by a subquery or an implicit query, such as a query in a WHERE clause. A subquery or implicit query in a DML statement is guaranteed to be consistent as of the start of the query and does not see the effects of the DML statement it is part of.



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