[Work In Progress] VReplicating JSON Columns: fix data loss with large NUMERIC and DECIMAL values

[rohit-nayak-ps]

Description

Motivation

Large fixed point NUMERIC and DECIMAL values in JSON Objects are not correctly vreplicated today. Such numbers are converted to a float64 by the binlog json parser.

So a json value like {"a": 12345678901234567890123456789012345678901234567890123456789012345678901234567890, "b": 987654321.012345678901234567890} on the source gets replicated like {"a": 1.2345678901234573e79, "b": 987654321.0123456}

Approach

VStreamer

The VStreamer needs to deserialize the binlog values exactly. This is done by adding support for fixed type integers and decimals in ajson, the library we use today to define a json value in an ast and stringify it while creating the correspondig VEvent.

VPlayer

The VPlayer needs to generate mysql queries so that MySQL retains precision.MySQL will only keep the true value of fixed point values if they are specified in a json_object() while inserting or updating. If they are just specified as a string representation, the mysql parser will convert it to a float and lose precision. Same holds for json arrays.

The snippets below illustrate the issue:

insert into jsontest values 
('{"a": 12345678901234567890123456789012345678901234567890123456789012345678901234567890,
 "b": 987654321.012345678901234567890}');

insert into jsontest values 
(json_object("a",12345678901234567890123456789012345678901234567890123456789012345678901234567890, 
"b", 987654321.012345678901234567890)); 

select * from jsontest;
+-------------------------------------------------------------------------------------------------------------------------------+
| j                                                                                                                             |
+-------------------------------------------------------------------------------------------------------------------------------+
| {"a": 1.2345678901234573e79, "b": 987654321.0123456}                                                                          |
| {"a": 12345678901234567890123456789012345678901234567890123456789012345678901234567890, "b": 987654321.012345678901234567890} |
+-------------------------------------------------------------------------------------------------------------------------------+

So we need to also generate json_object()s and json_array()s while inserting json (dictionary) objects and arrays so as to replicate the exact value.

Status

• VStreamer now generates data correctly for DECIMALS with a local change to ajson which has not yet been pushed to our ajson fork. VStreamer: improve representation of integers in json data types #12630 already fixed issues with large integers like 930701976723823 which would get vreplicated as 9.30701976723823e+14 and 1234567890 which would get vreplicated as 1234567890.0 .

• TODO:

Related Issue(s)

#8686

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[rohit-nayak-ps]

Closed in favor of #12761