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config, sysvar: map max-server-connections to max_connections #35453

Merged
merged 13 commits into from
Jun 23, 2022
Merged

config, sysvar: map max-server-connections to max_connections #35453

merged 13 commits into from
Jun 23, 2022

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CbcWestwolf
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@CbcWestwolf CbcWestwolf commented Jun 16, 2022 •
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What problem does this PR solve?

Issue Number: ref #34960

Problem Summary:

Before, if we want to change the limitation of max-server-connections, we have to change the configuration and restart the node. And the system variable max_connections is not available.

What is changed and how it works?

Add a new config item instance.max_connections and make sysvar max_connections available.

Check List

Tests

  • Unit test (using previous testing)
  • Integration test
  • Manual test (add detailed scripts or steps below)

Thanks @morgo for suggesting this manual test!

Test 1: check whether 'max_connections' limits the number of incoming connections:
1. start a tidb-server
2. start one mysql client connecting to the server with unlimited 'max_connections'
3. 'set @@global.max_connections = 3'
4. try to start other mysql clients connecting to the server one by one, until some errors happen.
Result: only three clients can connect to the server.
The later connections encounter 'ERROR 1040 (08004): Too many connections'

Test 2: check whether 'set @@global.max_connections = ?' success:
1. start a tidb-server
2. start 5 mysql clients connecting to the server with unlimited 'max_connections'
3. try to 'set @@global.max_connections = ?' using the number from 0 to 10
Result: whatever the value is, the setting is always successful. 
But if the setting value is bigger than the current connection number, no other connections can come in.
This behaviour is the same with MySQL.
  • No code

Side effects

  • Performance regression: Consumes more CPU
  • Performance regression: Consumes more Memory
  • Breaking backward compatibility

Documentation

  • Affects user behaviors
  • Contains syntax changes
  • Contains variable changes
  • Contains experimental features
  • Changes MySQL compatibility

For MySQL 8.0, the range of max_connections is [1, 100000], and the default value is 151. In TiDB, since the default value of instance.max_connections is 0, which means no limitation, so the range of max_connections in TiDB is [0, 100000], and default value is 0.

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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ti-chi-bot commented Jun 16, 2022 •
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[REVIEW NOTIFICATION]

This pull request has been approved by:

  • morgo
  • xiongjiwei

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

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@CbcWestwolf CbcWestwolf requested a review from a team as a code owner June 16, 2022 09:33
@ti-chi-bot ti-chi-bot added release-note-none Denotes a PR that doesn't merit a release note. size/M Denotes a PR that changes 30-99 lines, ignoring generated files. labels Jun 16, 2022
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/run-unit-test

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sre-bot commented Jun 16, 2022 •
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Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/eae00b1001584ac15c4fcabb6599e8ee1675efee

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/cc morgo bb7133 zimulala xiongjiwei

morgo
morgo reviewed Jun 16, 2022
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Looks great! Can you manual test as well: what happens when you have 10 idle connections on a server, and then you set the max_connections to 5? I assume from the code it takes effect on the next connection, and the existing connections work fine.

For another test: what happens when you have 10 idle, and set the max_connections to 12? Do 2 new connections come in with no problems, but the 13th breaks?

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morgo commented Jun 18, 2022

It looks like the error returned if connections is exceeded is not the best :( This might be an existing bug - here is what MySQL returns:

$ mysql
ERROR 1040 (HY000): Too many connections

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It looks like the error returned if connections is exceeded is not the best

Fixed it. Now the behavior is compatible with MySQL. PTAL :)

@ti-chi-bot ti-chi-bot added the status/LGT1 Indicates that a PR has LGTM 1. label Jun 20, 2022
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/run-unit-test

@ti-chi-bot ti-chi-bot added status/LGT2 Indicates that a PR has LGTM 2. and removed status/LGT1 Indicates that a PR has LGTM 1. labels Jun 21, 2022
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/merge

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This pull request has been accepted and is ready to merge.

Commit hash: 8a0a06d

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Jun 21, 2022
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xhebox commented Jun 21, 2022

/hold

@ti-chi-bot ti-chi-bot added the do-not-merge/hold Indicates that a PR should not merge because someone has issued a /hold command. label Jun 21, 2022
bb7133
bb7133 reviewed Jun 22, 2022
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server/server.go Outdated
// `EOF` means the connection is closed normally, we do not treat it as a noticeable error and log it in 'DEBUG' level.
logutil.BgLogger().With(zap.Uint64("conn", conn.connectionID)).
Debug("EOF", zap.String("remote addr", conn.bufReadConn.RemoteAddr().String()))
} else {
case errConCount:
_ = conn.writeError(ctx, err)
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Suggested change
_ = conn.writeError(ctx, err)
_ = conn.writeError(ctx, err)

Please handle the error here, you could simply write an log for it.

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Fixed. PTAL :)

@ti-chi-bot ti-chi-bot removed the status/can-merge Indicates a PR has been approved by a committer. label Jun 22, 2022
bb7133
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LGTM

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bb7133 commented Jun 23, 2022

/merge

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This pull request has been accepted and is ready to merge.

Commit hash: a975923

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Jun 23, 2022
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/unhold

@ti-chi-bot ti-chi-bot removed the do-not-merge/hold Indicates that a PR should not merge because someone has issued a /hold command. label Jun 23, 2022
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/run-unit-test

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/run-realtikv-test

@ti-chi-bot ti-chi-bot merged commit e2b5564 into pingcap:master Jun 23, 2022
@CbcWestwolf CbcWestwolf deleted the max_connections branch June 23, 2022 07:13
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sre-bot commented Jun 23, 2022

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name Result Duration Compare with Parent commit
idc-jenkins-ci-tidb/common-test 🟥 failed 1, success 11, total 12 12 min New failing
idc-jenkins-ci-tidb/integration-common-test 🔴 failed 1, success 10, total 11 19 min Existing failure
idc-jenkins-ci-tidb/integration-ddl-test 🔴 failed 1, success 5, total 6 14 min Existing failure
idc-jenkins-ci-tidb/tics-test 🔴 failed 1, success 0, total 1 4 min 14 sec Existing failure
idc-jenkins-ci/integration-cdc-test 🟢 all 35 tests passed 26 min Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2 🟢 all 28 tests passed 6 min 31 sec Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1 🟢 all 26 tests passed 5 min 59 sec Existing passed
idc-jenkins-ci-tidb/mybatis-test 🟢 all 1 tests passed 3 min 22 sec Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test 🟢 all 1 tests passed 3 min 11 sec Existing passed
idc-jenkins-ci-tidb/plugin-test 🟢 build success, plugin test success 4min Existing passed

morgo added a commit to morgo/tidb that referenced this pull request Jun 24, 2022
@morgo
Merge remote-tracking branch 'upstream/master' into add-bootstrap-sql
a0769dc 
* upstream/master: (38 commits)
  planner: disable collate clause support for enum or set column (pingcap#35684)
  *: Provide a util to "pause" session in uint test (pingcap#35529)
  ddl: implement the core for multi-schema change (pingcap#35429)
  parser: XXXDatabaseStmt now use CIStr for DB name (pingcap#35668)
  *: remove real tikv test on github actions (pingcap#35710)
  lightning: support disable scheduler by key range (pingcap#34130)
  Revert "planner: fix the wrong cost formula of MPPExchanger" (pingcap#35707)
  ddl, owner: refresh ddl sequence cache after becoming the owner (pingcap#35516)
  store/copr: fix tiflash integration test by disable paging on tiflash (pingcap#35674)
  planner: new cost formula for IndexJoin (pingcap#35671)
  BR: fix backup ranges total time summary log (pingcap#35552)
  raw_restore: fix the issue that raw restore rewrite the t prefix keys (pingcap#35641)
  table: fix cannot find the temp table when it's created in a transaction (pingcap#35663)
  metrics: replace histogram with counter for  DistSQLCoprCache (pingcap#35514)
  *: enable exportloopref  (pingcap#35680)
  types: fix bad error message for numeric conversion issue#32744 (pingcap#34047)
  *: enable ineffassign (pingcap#35670)
  config, sysvar: map `max-server-connections` to `max_connections` (pingcap#35453)
  *: enable durationcheck for nogo linter (pingcap#35661)
  *: fix issue of cast string as time is incompatible with MySQL (pingcap#35455)
  ...
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@morgo morgo morgo approved these changes

@bb7133 bb7133 bb7133 approved these changes

@xiongjiwei xiongjiwei xiongjiwei approved these changes

@zimulala zimulala Awaiting requested review from zimulala

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@CbcWestwolf @ti-chi-bot @sre-bot @morgo @xiongjiwei @xhebox @bb7133 @hawkingrei