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Fix decode error when "NULL" value in the column with "primary key" flag (#5879) #5938

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ti-chi-bot
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This is an automated cherry-pick of #5879

What problem does this PR solve?

Issue Number: close #5859

Problem Summary:
TiFlash assumes all values in the column with "primary key" flag are non-null value.

However, users could create such "NULL" value in the "primary key" column by following steps

-- create table with `source` is nullable
create table test.t_case (
`case_no` varchar(32) not null,
`source` varchar(20) default null,
`p` varchar(12) DEFAULT NULL,
primary key (`case_no`)
);

-- insert some data and left `source` to be empty
insert into test.t_case(case_no)
values ("1"), ("2"), ("3"), ("4");

-- drop the primary key, fill the `source` to be non-empty
alter table t_case drop primary key;
update test.t_case set `source` = '' where `source` is NULL;
-- add new primary key with case_no and source
alter table t_case add primary key (case_no, source);

-- send the snapshot data to tiflash
alter table t_case set tiflash replica 1;

What is changed and how it works?

  • mainly change the logic in addDefaultValueToColumnIfPossible
    • For non-clustered index table(is_common_handle=false && pk_is_handle=false), fill default value even if the column contains primary key flag when the column is not appear in the encoded value(those rows are not supposed to be return to users)
    • For clustered index/pk_is_handle table, ignore the primary key column as they are supposed to be decoded from the encoded key
  • Refine the exception message in insertRangeFrom
  • Add more region info when exception thrown in preHandleSnapshot/ingestSST

Check List

Tests

  • Unit test
  • Integration test
  • Manual test (add detailed scripts or steps below)
  • No code

Side effects

  • Performance regression: Consumes more CPU
  • Performance regression: Consumes more Memory
  • Breaking backward compatibility

Documentation

  • Affects user behaviors
  • Contains syntax changes
  • Contains variable changes
  • Contains experimental features
  • Changes MySQL compatibility

Release note

Fix the panic issue after creating the primary index with a column containing `NULL` value

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>
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[REVIEW NOTIFICATION]

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@ti-chi-bot ti-chi-bot added release-note Denotes a PR that will be considered when it comes time to generate release notes. do-not-merge/cherry-pick-not-approved size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. type/cherry-pick-for-release-5.0 labels Sep 16, 2022
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@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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@JaySon-Huang
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Close as the code change too much before merging the PR "Improve the efficiency of decode process of rows to columns"

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2 participants