Add docs for sysvar cache #5563

morgo · 2021-05-05T19:34:35Z

What is changed, added or deleted? (Required)

This is the docs for pingcap/tidb#24359 which has not merged yet. It more accurately reflects the future-state of sysvars.

There is another PR for GA releases which describes how it previously worked better: #5562

It needs a "followup" to insert the version the change is effective from.

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

master (the latest development version)
v5.1 (TiDB 5.1 versions) add "since v5.1" back
v5.0 (TiDB 5.0 versions)
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
Need modification after applied to another branch
Might cause conflicts after applied to another branch

TomShawn · 2021-05-06T03:04:06Z

/label for-future-release
/label requires-followup
/assign
/translation doing
/cc @zhangjinpeng1987 @xhebox

xhebox

Rest LGTM

xhebox · 2021-05-06T04:49:29Z

system-variables.md

@@ -25,8 +25,9 @@ SET  GLOBAL tidb_distsql_scan_concurrency = 10;

 > **Note:**
 >
-> TiDB differs from MySQL in that `GLOBAL` scoped variables **persist** through TiDB server restarts. Changes are also propagated to other TiDB servers every 2 seconds [TiDB #14531](https://github.com/pingcap/tidb/issues/14531).
-> Additionally, TiDB presents several MySQL variables from MySQL 5.7 as both readable and settable. This is required for compatibility, since it is common for both applications and connectors to read MySQL variables. For example: JDBC connectors both read and set query cache settings, despite not relying on the behavior.
+> <!-- Since next_version version --> Executing `SET GLOBAL` applies immediately on the TiDB server where the statement was issued. All TiDB servers in the cluster are sent a notification to refresh their global variables, which will begin immediately as a background operation.


All other TiDB servers, receive a notification, maybe?

BTW, I think it should be noted that the notification is immediate, but the refresh/eviction is not.

It's actually not "all other servers" but "all servers" (the initiating server will also receive the message too).

I used the language "begin immediately as a background operation" to indicate that it has no guarantee on completion time.

The notifications may not always succeed to be delivered to all the tidb instances.

@xhebox @tiancaiamao I have updated the wording. PTAL again, thx!

TomShawn · 2021-05-25T02:47:00Z

@xhebox PTAL again. Thanks!

TomShawn · 2021-05-31T09:43:53Z

/hold

qiancai · 2021-05-31T10:06:33Z

Hi @morgo, we are preparing the user docs for TiDB v5.1 and would like to know whether the doc changes of this PR apply to TiDB v5.1 or not. Would you please check and reply? Thanks!

morgo · 2021-05-31T14:10:01Z

Hi @morgo, we are preparing the user docs for TiDB v5.1 and would like to know whether the doc changes of this PR apply to TiDB v5.1 or not. Would you please check and reply? Thanks!

Yes, it is in 5.1.

qiancai · 2021-05-31T14:54:14Z

Hi @morgo, we are preparing the user docs for TiDB v5.1 and would like to know whether the doc changes of this PR apply to TiDB v5.1 or not. Would you please check and reply? Thanks!

Yes, it is in 5.1.

Got it. Thanks for the confirmation. I'll add the v5.1 label to identify this PR.

TomShawn · 2021-06-02T09:19:17Z

@xhebox @tiancaiamao @zhangjinpeng1987 PTAL, thanks!

xhebox

LGTM @TomShawn

system-variables.md

Co-authored-by: TomShawn <[email protected]>

morgo · 2021-06-09T00:46:02Z

@TomShawn this should be ready now

system-variables.md

Co-authored-by: TomShawn <[email protected]>

TomShawn

LGTM

ti-chi-bot · 2021-06-09T05:44:00Z

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TomShawn · 2021-06-09T05:45:27Z

/remove-status LGT1
/status LGT2

TomShawn · 2021-06-09T05:46:00Z

/merge

ti-chi-bot · 2021-06-09T05:46:03Z

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

Commit hash: 5738e3c

Liuxiaozhen12 · 2021-06-17T03:38:23Z

/remove-translation doing
/translation done

Add docs for sysvar cache

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domain, session: Add new sysvarcache to replace global values cache pingcap/tidb#24359

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update wording

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This was referenced Jun 17, 2021

Liuxiaozhen patch 1 pingcap/docs-cn#6463

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Add docs for sysvar cache pingcap/docs-cn#6464

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domain, session: Add new sysvarcache to replace global values cache (#24359) pingcap/tidb#26030

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Add docs for sysvar cache #5563

Add docs for sysvar cache #5563

morgo commented May 5, 2021 •

edited by TomShawn

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Add docs for sysvar cache #5563

Add docs for sysvar cache #5563

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morgo commented May 5, 2021 • edited by TomShawn Loading

What is changed, added or deleted? (Required)

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Do your changes match any of the following descriptions?

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