stmt-reference, sysvars: Document dml-batch-size

[ghost]

What is changed, added or deleted? (Required)

Part of #3155

Only relevant to master.

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Have version specific changes
• Might cause conflicts

[ghost]

It looks like this was removed in #1806 , but it needs to be added back because of the upgrade issue mentioned here :(

[jackysp]

lgtm

[cfzjywxk]

LGTM

[ti-srebot]

@cfzjywxk,Thanks for your review. However, LGTM is restricted to Reviewers or higher roles.See the corresponding SIG page for more information. Related SIG: docs(slack).

[TomShawn]

LGTM

[TomShawn]

@nullnotnil Could you explain what example value is? I find it confusing when reviewing the translation of this PR. From the context, 20000 does not appear in this document but in sql-statement-load-data.md . Did you mean the example in sql-statement-load-data.md ?

[ghost]

I picked 20000 as an example value because this is the prior batch size for LOAD DATA before it was changed to not be batched in master.

I think it is potentially useful for other sysvars, because the min/max values may be a very wide range.

[TomShawn]

Can we say In earlier releases of TiDB, the default batch size for LOAD DATA was 20000? Here the example seems a little confusing.

[ghost]

Let's just remove it. I don't think people will know to look up this value when they get an error, they will look up the reference for LOAD DATA, which mentions the previous default.

[TomShawn]

Removed in #3977.