server: add sql to com_exec/com_fetch dispatch error log

[lysu]

What problem does this PR solve?

More and more user use prepare stmt, but current dispatch error log we only can see packet binary info, we don't know which sql meet error.

What is changed and how it works?

add sql to error thrown in handleStmtExec and handleStmtFetch

after this PR, we can got

[2019/09/12 15:38:43.715 +08:00] [WARN] [conn.go:669] ["command dispatched failed"] [conn=1] [connInfo="id:1, addr:127.0.0.1:43540 status:2, collation:utf8_general_ci, user:root"] [command=Fetch] [sql="\u0001\u0000\u0000\u0000\u0001\u0000\u0000\u0000"] [err="12121\ngithub.jparrowsec.cn/pingcap/tidb/server.(*clientConn).handleStmtFetch\n\t/home/robi/code/go/src/github.com/pingcap/tidb/server/conn_stmt.go:239\ngithub.jparrowsec.cn/pingcap/tidb/server.(*clientConn).dispatch\n\t/home/robi/code/go/src/github.com/pingcap/tidb/server/conn.go:914\ngithub.jparrowsec.cn/pingcap/tidb/server.(*clientConn).Run\n\t/home/robi/code/go/src/github.com/pingcap/tidb/server/conn.go:653\ngithub.jparrowsec.cn/pingcap/tidb/server.(*Server).onConn\n\t/home/robi/code/go/src/github.com/pingcap/tidb/server/server.go:438\nruntime.goexit\n\t/home/robi/runtime/go/src/runtime/asm_amd64.s:1337\nselect 1"]

("select 1" now is in last, we can modify pingcap/errors to let be in front, but we need add msg first)

Check List

Tests

• Unit test
• Integration test

Code changes

• wrap error message with sql

Side effects

• N/A

Related changes

• Need to cherry-pick to the release branch

Release note

• server: add sql to com_exec/com_fetch dispatch error log

---

This change is 

[lysu]

/run-all-tests

[ngaut]

Could you remove the stack error message, it feels like noise.

[codecov]

Codecov Report

Merging #12174 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #12174   +/-   ##
===========================================
  Coverage   81.2778%   81.2778%           
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  Files           454        454           
  Lines         98290      98290           
===========================================
  Hits          79888      79888           
  Misses        12682      12682           
  Partials       5720       5720

[lysu]

Could you remove the stack error message, it feels like noise.

maybe we'd better not remove stack in for this case, stack in "dispatch error" is useful for troubleshooting.

for example, some low-level method returns std error(e.g. DeadlineExceeded) and error goes up to top-level dispatch method return short error to user and write detail dispatch error log, without stack we may hard to identity error is thrown in A or B logic(e.g. pdclient or tikvclient). IMHO, if different components throw the different error is ok, but when different components can throw the same error and we want to log it in one place(like this entrance method), maybe we need stack to identity.

we should let sql in front of stack info.

[lysu]

this previous log example is generated by with-stack error.

if we can make sure the error no need stack(e.g. KeyDuplicateError) we can use errors.SuspendStack to foribid stack for special error, fot that error, log will be

[conn.go:669] ["command dispatched failed"] [conn=1] [connInfo="id:1, addr:127.0.0.1:45114 status:2, collation:utf8_general_ci, user:root"] [command=Fetch] [sql="\u0001\u0000\u0000\u0000\u0001\u0000\u0000\u0000"] [err="12121\nselect 1"]

[jackysp]

LGTM

[tiancaiamao]

LGTM

[sre-bot]

/run-all-tests

[sre-bot]

cherry pick to release-3.1 in PR #12189

[sre-bot]

cherry pick to release-3.0 in PR #12191

[lysu]

/run-cherry-picker

[sre-bot]

cherry pick to release-2.1 failed

[sre-bot]

It seems that, not for sure, we failed to cherry-pick this commit to release-2.1. Please comment '/run-cherry-picker' to try to trigger the cherry-picker if we did fail to cherry-pick this commit before. @lysu PTAL.