*: TIDB_DECODE_KEY(): Decode keys which only have a TableID

[dveeden]

What problem does this PR solve?

The TIDB_DECODE_KEY() function was only able to decode keys that were "record" or "index" keys. However the START_KEY and END_KEY columns of information_schema.TIKV_REGION_STATUS always have entries that only have a "table_id" and no row/index info. This is for the minimum start key and the maximum end key.

This change:

• Helps to decode entries that only have an table_id like 7480000000000000FF4700000000000000F8
• Removes warnings for calling TIDB_DECODE_ROW() on the minimum START_KEY and maximum END_KEY.
• Removes invalid JSON values that are returned by TIDB_DECODE_ROW() for the minimum START_KEY and maximum END_KEY. This allows one to use JSON functions directly without having to use IF(JSON_VALID(),...

This is related to pingcap/docs#6728

Check List

Tests

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

sql> SELECT TIDB_DECODE_KEY('7480000000000000FF4700000000000000F8');
+---------------------------------------------------------+
| TIDB_DECODE_KEY('7480000000000000FF4700000000000000F8') |
+---------------------------------------------------------+
| {"table_id":71}                                         |
+---------------------------------------------------------+
1 row in set (0.0013 sec)

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

TIDB_DECODE_KEY() now works on keys that only have a Table ID

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• kennytm
• tangenta

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[dveeden]

/cc @kolbe

[dveeden]

/cc @tangenta

[dveeden]

/run-check_dev
/run-check_dev_2

[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: e264bb0

[ti-chi-bot]

@dveeden: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[kennytm]

/run-check_dev_2

🤔 https://ci.pingcap.net/blue/organizations/jenkins/tidb_ghpr_check_2/detail/tidb_ghpr_check_2/43863/pipeline

[2021-11-07T15:38:01.515Z] --- FAIL: TestCacheTableBasicScan (3.75s)
[2021-11-07T15:38:01.515Z]     result.go:50: 
[2021-11-07T15:38:01.515Z]         	Error Trace:	result.go:50
[2021-11-07T15:38:01.515Z]         	            				cache_test.go:79
[2021-11-07T15:38:01.515Z]         	            				cache_test.go:113
[2021-11-07T15:38:01.515Z]         	Error:      	Not equal: 
[2021-11-07T15:38:01.515Z]         	            	expected: "[UnionScan 3333.33 root  gt(test.tmp1.id, 4)]\n[└─TableReader 3333.33 root  data:TableRangeScan]\n[  └─TableRangeScan 3333.33 cop[tikv] table:tmp1 range:(4,+inf], keep order:true, stats:pseudo]\n"
[2021-11-07T15:38:01.515Z]         	            	actual  : "[TableReader 3333.33 root  data:TableRangeScan]\n[└─TableRangeScan 3333.33 cop[tikv] table:tmp1 range:(4,+inf], keep order:true, stats:pseudo]\n"
[2021-11-07T15:38:01.515Z]         	            	
[2021-11-07T15:38:01.515Z]         	            	Diff:
[2021-11-07T15:38:01.515Z]         	            	--- Expected
[2021-11-07T15:38:01.515Z]         	            	+++ Actual
[2021-11-07T15:38:01.515Z]         	            	@@ -1,4 +1,3 @@
[2021-11-07T15:38:01.515Z]         	            	-[UnionScan 3333.33 root  gt(test.tmp1.id, 4)]
[2021-11-07T15:38:01.515Z]         	            	-[└─TableReader 3333.33 root  data:TableRangeScan]
[2021-11-07T15:38:01.515Z]         	            	-[  └─TableRangeScan 3333.33 cop[tikv] table:tmp1 range:(4,+inf], keep order:true, stats:pseudo]
[2021-11-07T15:38:01.515Z]         	            	+[TableReader 3333.33 root  data:TableRangeScan]
[2021-11-07T15:38:01.515Z]         	            	+[└─TableRangeScan 3333.33 cop[tikv] table:tmp1 range:(4,+inf], keep order:true, stats:pseudo]