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add document about stale read transaction #6347

Merged
merged 59 commits into from
Jun 15, 2021
Merged

add document about stale read transaction #6347

merged 59 commits into from
Jun 15, 2021

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Yisaer
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@Yisaer Yisaer commented May 27, 2021 •
edited by TomShawn
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What is changed, added or deleted? (Required)

add document about stale read transaction

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@Yisaer
add doc
00fb603 
Signed-off-by: yisaer <disxiaofei@163.com>
@Yisaer
add sql view
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@ti-chi-bot ti-chi-bot requested a review from TomShawn May 27, 2021 06:21
@ti-chi-bot ti-chi-bot added missing-translation-status This PR does not have translation status info. size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. labels May 27, 2021
@Yisaer
add sql view
dc84157 
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@Yisaer
fix lint
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@Yisaer
fix lint
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@TomShawn TomShawn added v5.1 This PR/issue applies to TiDB v5.1. translation/doing This PR’s assignee is translating this PR. labels May 27, 2021
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@Yisaer
fix lint
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@TomShawn TomShawn requested a review from nolouch May 27, 2021 06:43
@TomShawn TomShawn added the status/PTAL This PR is ready for reviewing. label May 27, 2021
@Yisaer
fix lint
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@Yisaer
fix lint
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nolouch
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JmPotato
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@TomShawn TomShawn added status/require-change Needs the author to address comments. and removed status/PTAL This PR is ready for reviewing. labels Jun 1, 2021
@JmPotato
Add Stale Read introduction
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Resolve the conflict
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Fix the link
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Fix a typo
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nolouch
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kissmydb
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+ 场景二：在一些小表的查询场景中，如果使用了强一致性读，数据可能集中在某一个存储节点上，导致查询压力集中在该节点，成为整个查询的瓶颈。使用 Stale Read 功能后，TiDB 可以将请求分发到对应数据的每一个副本上，提升了查询整体的吞吐能力，从而显著提升查询性能。

+ 场景三：在部分跨数据中心部署的场景中，如果使用了强一致性的 Follower 读，为了读到的数据与 Leader 上的数据一致，会产生跨数据中心获取 Readindex 来校验的请求，导致整体查询的访问延迟增加。通过使用 Stale Read 功能，可以牺牲一定的实时性，可就近访问对应数据所在当前中心的副本，避免跨数据中心的网络延迟，降低整体查询的访问延迟。
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针对场景三，就近读取到一个尽可能新的数据即可，一定要改 sql，加上「as of timestamp」么，还要明确指定一个时间？

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只要使用 Stale read 功能，就要改 SQL，和哪个场景没关系。

@Yisaer
add local read
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add local read

Signed-off-by: yisaer <disxiaofei@163.com>
nolouch
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/lgtm

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TomShawn
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Apply suggestions from code review
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LGTM

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/remove-status LGT1
/status LGT2

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/merge

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

Commit hash: 84ddbea

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Jun 15, 2021
@TomShawn TomShawn removed the status/require-change Needs the author to address comments. label Jun 15, 2021
@ti-chi-bot ti-chi-bot merged commit c984ed2 into pingcap:master Jun 15, 2021
@TomShawn TomShawn assigned CharLotteiu and unassigned qiancai Jun 16, 2021
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@CharLotteiu This PR is further updated in #6453. Please also translate the update. Thanks!

@CharLotteiu CharLotteiu mentioned this pull request Jun 18, 2021
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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 Jun 18, 2021
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as-of-timestamp.md

## 示例

本节通过多个示例介绍 `AS OF TIMESTAMP` 语法的不同使用方法。在本节中，先介绍如何准备用于恢复的数据，再分别展示如何通过 `SELECT`、`START TRANSACTION READ ONLY AS OF TIMESTAMP`、`SET TRANSACTION READ ONLY AS OF TIMESTAMP` 以及 `SELECT` 子句使用 `AS OF TIMESTAMP`。
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及 SELECT 子句

TomShawn
TomShawn reviewed Jun 21, 2021
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best-practices/three-dc-local-read.md

# 在三数据中心下就近读取数据

在三数据中心模式下，Region 的三个副本都会隔离在各个数据中心里。然而在强一致读的要求下，tidb 的每一个查询都需要访问对应数据的 Leader 副本，而查询的来源可能和 Leader 所在的数据中心不一致，这就会引起跨数据中心的数据访问，从而造成访问的延迟上升。本文主要介绍使用 [Stale Read](/stale-read.md) 功能，以牺牲数据实时性的方式，避免跨数据中心的访问，从而降低访问的延迟。
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tidb -> TiDB

@ti-chi-bot ti-chi-bot mentioned this pull request Jun 23, 2021
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