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reference: add new option for tidb_replica_read #2252

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merged 2 commits into from
Apr 15, 2020
Merged

reference: add new option for tidb_replica_read #2252

merged 2 commits into from
Apr 15, 2020

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hicqu
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@hicqu hicqu commented Apr 13, 2020

What is changed, added or deleted? (Required)

Add an new option for tidb_replica_read.

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)
  • v3.0 (TiDB 3.0 versions)
  • v2.1 (TiDB 2.1 versions)

What is the related PR or file link(s)?

pingcap/tidb#15721

  • This PR is translated from:
  • Other reference link(s):

@hicqu
follower read: add new option for tidb_replica_read
b6c7509 
Signed-off-by: qupeng <qupeng@pingcap.com>
zhangjinpeng87
zhangjinpeng87 reviewed Apr 13, 2020
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reference/performance/follower-read.md
@@ -34,6 +34,7 @@ This variable is used to set the data read mode expected by the current session.

- When the value of `tidb_replica_read` is set to `leader` or an empty string, TiDB maintains its original behavior and sends all read operations to the leader replica to perform.
- When the value of `tidb_replica_read` is set to `follower`, TiDB selects a follower replica of the Region to perform all read operations.
- When the value of `tidb_replica_read` is set to `leader-and-follower`, TiDB can select any replicas to perform read operations.
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Not include learner replica

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Learners are included. In fact follower also includes them.

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leader-and-follower also can read learner?

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Both leader-and-follower and follower can read learner.

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How about if a learner doesn't have enough data? For example, the replica is in balancing status.

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@hicqu hicqu Apr 13, 2020 •
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If it's applying a snapshot, new proposals will be dropped and TiDB clients will switch to a next peer.

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can we optimize it latter? For example, peer could report its status to pd, and TiDB will not choose the peer who is applying a snapshot (or not ready).

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Good idea. Seems it's possible.

@TomShawn TomShawn self-assigned this Apr 13, 2020
@TomShawn TomShawn added size/small Changes of a small size. translation/doing This PR's assignee is translating this PR. labels Apr 13, 2020
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TomShawn commented Apr 13, 2020 •
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@hicqu Please specify all the affected document versions. If the change in this PR also applies to dev, please create another PR to make this change to dev, thanks!

zhangjinpeng87
zhangjinpeng87 approved these changes Apr 15, 2020
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LGTM

@hicqu hicqu merged commit b282ca8 into release-3.1 Apr 15, 2020
@hicqu hicqu deleted the 3.1-replica-new_option branch April 15, 2020 06:53
sre-bot pushed a commit to sre-bot/docs that referenced this pull request Apr 15, 2020
@hicqu @sre-bot
follower read: add new option for tidb_replica_read (pingcap#2252)
b3aa950 
Signed-off-by: qupeng <qupeng@pingcap.com>
@sre-bot sre-bot mentioned this pull request Apr 15, 2020
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sre-bot commented Apr 15, 2020

cherry pick to release-4.0 in PR #2283

@TomShawn TomShawn changed the title follower read: add new option for tidb_replica_read reference: add new option for tidb_replica_read Apr 15, 2020
@TomShawn TomShawn mentioned this pull request Apr 15, 2020
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@TomShawn TomShawn added translation/done This PR has been translated from English into Chinese and updated to pingcap/docs-cn in a PR. and removed translation/doing This PR's assignee is translating this PR. labels Apr 15, 2020
TomShawn pushed a commit that referenced this pull request Apr 23, 2020
@sre-bot @hicqu @shenli
follower read: add new option for tidb_replica_read (#2252) (#2283)
fb35027 
Signed-off-by: qupeng <qupeng@pingcap.com>

Co-authored-by: qupeng <qupeng@pingcap.com>
Co-authored-by: Shen Li <shenli3514@gmail.com>
This was referenced May 14, 2020
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@TomShawn TomShawn mentioned this pull request Jun 10, 2020
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