auto-increment: change "continuous" to monotonic

[ghost]

What is changed, added or deleted? (Required)

The AUTO_INCREMENT doc used the word "continuous" when it should be "monotonic". Continuous means "without any abrupt changes", i.e. at a constant rate (which could be up or down). Auto_increment is not really constant - since restarts could make values jump quite a bit. So could requesting a new batch of cached values.

Monotonic means "either never decreases or never increases". Which is the property it guarantees on a per-server basis.

The language will need version-specific changes because it says "30 thousand by default", but it needs to be 30 thousand explicitly for 2.1 which does not support AUTO_ID_CACHE.

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): The file does not exist in the earlier three 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

[kolbe]

LGTM

[ti-srebot]

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

[ti-srebot]

@kolbe, PTAL.

[lilin90]

LGTM

[lilin90]

@nullnotnil I suggest updating v3.1, v3.0, v2.1 in another PR. That would be easier.

[ti-srebot]

cherry pick to release-4.0 in PR #3647

[ghost]

It looks like the auto-increment docs are not present in 3.1 and below. They are still relevant, but if nobody has requested docs for it yet - I will leave it at this PR + the 4.0 cherry pick.

[lilin90]

It looks like the auto-increment docs are not present in 3.1 and below. They are still relevant, but if nobody has requested docs for it yet - I will leave it at this PR + the 4.0 cherry pick.

@nullnotnil I think that's ok.

[tangenta]

@nullnotnil Hi, I think the concept "monotonic" has been explained in the increment part.

This section does illustrate the "continuous" feature:

create table t (a int primary key AUTO_INCREMENT);
insert into t values (), (), (), ();
select * from t;
+---+
| a |
+---+
| 1 |
| 2 |
| 3 |
| 4 |
+---+

[ghost]

@nullnotnil Hi, I think the concept "monotonic" has been explained in the increment part.

This section does illustrate the "continuous" feature:

create table t (a int primary key AUTO_INCREMENT);
insert into t values (), (), (), ();
select * from t;
+---+
| a |
+---+
| 1 |
| 2 |
| 3 |
| 4 |
+---+

Thanks! I will attempt another PR to merge the two. It is better not to call it "continuous" still, because a user might rely on that behavior incorrectly.