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planner: support stable result mode #25971

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merged 13 commits into from
Jul 6, 2021

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@qw4990 qw4990 commented Jul 5, 2021

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary: support stable result mode in the planner

What is changed and how it works?

Results of some queries are not stable, for example:

create table t (a int);
insert into t values (1), (2);
select a from t;

In the case above, the result can be 1 2 or 2 1, which is not stable.
This PR introduces a new switch that can make the results of these queries stable.

This feature is implemented as a logical optimization rule, which stabilizes results by modifying Sort in plans or inject new Sort into plans.
First, all operators are divided into 2 types:

  1. input-order keepers: Selection, Projection, Limit;
  2. all other operators.

The basic idea of this rule is:

  1. iterate the plan from the root, and ignore all input-order keepers;
  2. when meeting the first non-input-order keeper,
    2.1. if it's a Sort, complete it by appending its output columns into its order-by list,
    2.2. otherwise, inject a new Sort upon this operator.

Check List

Tests

  • Unit test

Release note

  • planner: support stable result mode

@qw4990 qw4990 added type/enhancement The issue or PR belongs to an enhancement. sig/planner SIG: Planner labels Jul 5, 2021
@qw4990 qw4990 requested review from winoros and rebelice July 5, 2021 10:06
@ti-chi-bot ti-chi-bot added the size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. label Jul 5, 2021
@github-actions github-actions bot added the sig/execution SIG execution label Jul 5, 2021
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Hope we can remove this one day :(

@ti-chi-bot ti-chi-bot added the status/LGT1 Indicates that a PR has LGTM 1. label Jul 6, 2021
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[REVIEW NOTIFICATION]

This pull request has been approved by:

  • time-and-fate
  • winoros

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@ti-chi-bot ti-chi-bot added status/LGT2 Indicates that a PR has LGTM 2. and removed status/LGT1 Indicates that a PR has LGTM 1. labels Jul 6, 2021
qw4990 and others added 2 commits July 6, 2021 14:58
Co-authored-by: Zhou Kunqin <25057648+time-and-fate@users.noreply.github.com>
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qw4990 commented Jul 6, 2021

/merge

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This pull request has been accepted and is ready to merge.

Commit hash: d36a1a9

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Jul 6, 2021
@ti-chi-bot ti-chi-bot merged commit c24a90f into pingcap:master Jul 6, 2021
ti-srebot pushed a commit to ti-srebot/tidb that referenced this pull request Jul 6, 2021
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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cherry pick to release-4.0 in PR #25994

ti-srebot pushed a commit to ti-srebot/tidb that referenced this pull request Jul 6, 2021
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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cherry pick to release-5.1 in PR #25995

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qw4990 commented Jul 8, 2021

/run-cherry-picker

ti-srebot pushed a commit to ti-srebot/tidb that referenced this pull request Jul 8, 2021
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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cherry pick to release-5.0 in PR #26055

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