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https://issues.apache.org/jira/browse/IGNITE-6024?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16198543#comment-16198543
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Alexander Paschenko commented on IGNITE-6024:
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[~skalashnikov], my comments:
1. Why has {{UpdatePlan}} become mutable? As before, it's initialized fully in
one place. Please refactor to return immutability.
2. Why {{GridH2DmlResponse}} carries only error string? We already have had to
pull error code to thin JDBC response, probably we should preserve code here
too? [~vozerov], what do you think?
3. What is semantic of distributed {{MERGE}} or {{INSERT}} without subquery? If
I issue {{MERGE INTO Person(id, name) values (1, 'a'), (2, 'b'), (3, 'c')}},
how it will work? I don't see any code that would check this. Intuitively, it
should be somewhere around {{DmlStatementsProcessor#checkPlanCanBeDistributed}}.
4. {{DmlStatementsProcessor#checkPlanCanBeDistributed}}: why we don't care
about statements caching here? ({{PreparedStatement stmt =
conn.prepareStatement(plan.selectQry)}}) - looks like this could introduce an
inevitable parsing.
5. Option name {{updateOnServer}} looks confusing to me. Isn't something like
{{distributedDml}} better?
> SQL: execute DML statements on the server when possible
> -------------------------------------------------------
>
> Key: IGNITE-6024
> URL: https://issues.apache.org/jira/browse/IGNITE-6024
> Project: Ignite
> Issue Type: Task
> Components: sql
> Affects Versions: 2.1
> Reporter: Vladimir Ozerov
> Assignee: Sergey Kalashnikov
> Labels: important, performance
> Fix For: 2.3
>
>
> Currently we execute DML statements as follows:
> 1) Get query result set to the client
> 2) Construct entry processors and send them to servers in batches
> This approach is inefficient as it causes a lot of unnecessary network
> communication Instead, we should execute DML statements directly on server
> nodes when it is possible.
> Implementation considerations:
> 1) Determine set of queries which could be processed in this way. E.g.,
> {{LIMIT/OFFSET}}, {{GROUP BY}}, {{ORDER BY}}, {{DISTINCT}}, etc. are out of
> question - they must go through the client anyway. Probably
> {{skipMergeTable}} flag is a good starting point (good, not precise!)
> 2) Send request to every server and execute local DML right there
> 3) No failover support at the moment - throw "partial update" exception if
> topology is unstable
> 4) Handle partition reservation carefully
> 5) Transactions: we still have single coordinator - this is a client. When
> MVCC and TX SQL is ready, client will assign proper counters to server
> requests.
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