Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.4
Description
JSON_DETAILED function (https://mariadb.com/kb/en/library/json_detailed/ ) is described as
Represents JSON in the most understandable way emphasizing nested structures.
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We now got a use case for it: Optimizer Trace output. Optimizer trace is too large to be copied in full, instead we use expressions like
select
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JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
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Our experience is that JSON_DETAILED has some room for improvement when it comes to the quality of automatic JSON formatting.
Example:
source mdev19160-data.sql
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mysql> select JSON_DETAILED(JSON_EXTRACT(a, '$**.analyzing_range_alternatives')) from t200\G
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*************************** 1. row ***************************
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JSON_DETAILED(JSON_EXTRACT(a, '$**.analyzing_range_alternatives')): [
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{
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"range_scan_alternatives":
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[
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{
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"index": "a_b",
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"ranges":
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[
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"2 <= a <= 2 AND 4 <= b <= 4"
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],
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"rowid_ordered": true,
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"using_mrr": false,
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"index_only": true,
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"rows": 1,
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"cost": 1.1752,
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"chosen": true
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}
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],
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"analyzing_roworder_intersect":
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{
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"cause": "too few roworder scans"
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},
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"analyzing_index_merge_union":
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[
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]
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}
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]
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Things to note:
- empty lines at the start (right before/after the "range_scan_alternatives")
- "analyzing_index_merge_union":[] occupies 3 lines where one would be sufficient.
- the same goes for "ranges"
One can look at the JSON pretty-printer that is used by EXPLAIN FORMAT=JSON and optimizer trace. It produces a better result (but it has room for improvement, too.)
Extra: in MySQL, the function is called JSON_PRETTY. We should add ability to use this name as an alias.
Attachments
Issue Links
- is part of
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MDEV-28906 MySQL 8.0 desired compatibility
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- Open
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- relates to
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- Closed
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