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https://issues.apache.org/jira/browse/PHOENIX-3471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15688278#comment-15688278
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James Taylor commented on PHOENIX-3471:
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This is great, [~gabriel.reid]. This will definitely eliminate the brittleness
of our explain plan tests. I think the programatic access is ideal for tests,
but it would potentially have other uses too. It's possible that you'd want to
disallow certain types of queries from running if they're doing an operation
that is deemed "too expensive" (i.e. full table scan, sort, scan more than X
bytes). Is the "cost" of a query included in the explain plan? That would be
interesting to be able to access that as well.
The main things we test for are: table used in scan, type of table (i.e. local
index) since the same physical table will show up for a local index (see
PHOENIX-3344), type of scan (reverse, small, no_cache), start/stop row of scan
(or ideally the PK value extracted from this as done by ExplainTable), number
of splits/guideposts, estimated number of rows & bytes scanned, type of
aggregation (ungrouped, group, ordered grouped), sort info (may already show
up). I might be forgetting a few. Would be awesome if this could all be
incorporated into the explain plan.
> Allow accessing full (legacy) Phoenix EXPLAIN information via Calcite
> ---------------------------------------------------------------------
>
> Key: PHOENIX-3471
> URL: https://issues.apache.org/jira/browse/PHOENIX-3471
> Project: Phoenix
> Issue Type: Sub-task
> Reporter: Gabriel Reid
> Assignee: Gabriel Reid
>
> The EXPLAIN syntax in Calcite-Phoenix (either "EXPLAIN <sql>" or "EXPLAIN
> PLAN FOR <sql>") currently returns the Calcite plan for a query. For example:
> {code}
> EXPLAIN SELECT MAX(I) FROM T1
> {code}
> results in the following Calcite explain plan:
> {code}
> PhoenixToEnumerableConverter
> PhoenixServerAggregate(group=[{}], EXPR$0=[MAX($0)])
> PhoenixTableScan(table=[[phoenix, T1]])
> {code}
> and the following (legacy) Phoenix explain plan:
> {code}
> CLIENT PARALLEL 1-WAY FULL SCAN OVER T1
> SERVER FILTER BY FIRST KEY ONLY
> {code}
> There are currently a large number of integration tests which depend on the
> legacy Phoenix format of explain plan, and this format is no longer available
> when running via Calcite. PHOENIX-3105 added support for accessing the
> explain plan via the "EXPLAIN <sql>" syntax, but this update to the syntax
> still only provides the Calcite-specific explain plan.
> There are three main approaches which can be taken here:
> h4. Option 1: Custom EXPLAIN execution
> This approach extends the work done in PHOENIX-3105 to plug in a custom
> SqlPhoenixExplain
> node which returns the legacy Phoenix explain plan, with the "EXPLAIN PLAN
> FOR <sql>"
> syntax still returning the Calcite explain plan.
> h4. Option 2: Add the legacy Phoenix explain plan to the Calcite plan as a
> top-level attribute
> This approach results in an explain plan that looks as follows:
> {code}
> PhoenixToEnumerableConverter(PhoenixExecutionPlan=[CLIENT PARALLEL 1-WAY FULL
> SCAN OVER T1
> SERVER FILTER BY FIRST KEY ONLY])
> PhoenixServerAggregate(group=[{}], EXPR$0=[MAX($0)])
> PhoenixTableScan(table=[[phoenix, T1]])
> {code}
> The disadvantage of this approach is that it's not really "correct" -- we're
> just tacking
> a different representation of the explain plan into the Calcite explain plan.
> The advantage of this approach is that it's very quick and easy to implement
> (i.e. it
> can be done immediately), and it will require minimal changes to the many
> test cases which have
> hard-coded explain plans that things are checked against. All we need to do
> is have a
> utility to extract the PhoenixExecutionPlan value from the full Calcite plan,
> and other
> than that all test cases stay the same.
> h4. Option 3: Add all relevant information to the correct parts of the
> Calcite explain plan
> This approach would result in an explain plan that looks as follows:
> {code}
> PhoenixToEnumerableConverter
> PhoenixServerAggregate(group=[{}], EXPR$0=[MAX($0)])
> PhoenixTableScan(table=[[phoenix, T1]], scanType[CLIENT PARALLEL 1-WAY
> FULL ])
> {code}
> This is undoubtedly the "right" way to do things. However, it has the major
> disadvantage
> that it will require a large amount of work to do the following:
> * add all relevant information into various implementations of
> {{AbstractRelNode.explainTerms}}
> * rework all test cases which verify things against an expected explain plan
> It is of course also an option is to start with option 2 here, and eventually
> migrate to option 3.
> If we go for option 2 or option 3, we should probably remove the custom
> EXPLAIN parsing.
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