writing to ETCD may break the liner consistence

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Suppose we want to do:

Put a  1
Put a  2
Check if a is 2.

If there is some network problem during the first Put, we retry it. Things may become:

Put a 1 (timeout)
Put a 1 (retry)
Put a 2 
put a 1 (the timeout put arrive server)
Check if a is 2, fail.

2. What did you expect to see? (Required)

Make sure liner consistence. a == 2.

3. What did you see instead (Required)

a == 1.

4. What is your TiDB version? (Required)

All

[aytrack]

/label component/ddl
/label severity/major

[ti-chi-bot]

@aytrack: The label(s) component/ddl, severity/major cannot be applied. These labels are supported: fuzz/sqlancer, challenge-program, compatibility-breaker, first-time-contributor, contribution, require-LGT3, good first issue, correctness, duplicate, proposal, security, needs-more-info, needs-cherry-pick-release-5.3, needs-cherry-pick-release-5.4, needs-cherry-pick-release-6.0, needs-cherry-pick-release-6.1, needs-cherry-pick-release-6.2, needs-cherry-pick-release-6.3, needs-cherry-pick-release-6.4, needs-cherry-pick-release-6.5, needs-cherry-pick-release-6.6, needs-cherry-pick-release-7.0, needs-cherry-pick-release-7.1, needs-cherry-pick-release-7.2, needs-cherry-pick-release-7.3, affects-5.3, affects-5.4, affects-6.0, affects-6.1, affects-6.2, affects-6.3, affects-6.4, affects-6.5, affects-6.6, affects-7.0, affects-7.1, affects-7.2, affects-7.3, may-affects-5.3, may-affects-5.4, may-affects-6.0, may-affects-6.1, may-affects-6.2, may-affects-6.3, may-affects-6.4, may-affects-6.5, may-affects-6.6, may-affects-7.0, may-affects-7.1, may-affects-7.2, may-affects-7.3.

In response to this:

/label component/ddl
/label severity/major

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[jebter]

/component ddl
/severity major