From 2cdc887bcd590a9e4c9a3a03e1378d87eb8bcfbf Mon Sep 17 00:00:00 2001
From: zhangjinpeng1987 <zhangjinpeng@pingcap.com>
Date: Thu, 13 Jan 2022 21:08:39 +0800
Subject: [PATCH 1/2] PD: supports multiple level meta data space

Signed-off-by: zhangjinpeng1987 <zhangjinpeng@pingcap.com>
---
 text/0083-multi-level-meta-data-space.md | 52 ++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 text/0083-multi-level-meta-data-space.md

diff --git a/text/0083-multi-level-meta-data-space.md b/text/0083-multi-level-meta-data-space.md
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+# Multi-level Meta Data Space
+
+## Summary
+
+PD can handle multiple users' meta data, each user only see its own meta data.
+
+## Motivation
+
+PD is the mata data center of TiKV Cluster, the meta data contains TiKV instances' addr, user data range(region)
+information, the number of replicas of data, etc.
+
+But PD currently only can handle the key space [min-key, max-key], it means that PD only can handle one user's 
+meta data, it is not possible when multiple users want share the same PD cluster as their meta system. There are
+two different scenarios that require PD can handle multiple user' meta data:
+
+1. Multiple TiKV Cluster share the same PD cluster. Because the minimal demplyment of a TiKV Cluster is 3 TiKV 3 PD,
+but it is not cost-effect if every small cluster has 3 dedicated meta data node.
+2. There are Multiple tenant in the same TiKV Cluster, each tenant has it own meta data, each tenant's key range can
+contains any key in the range of [min-key, max-key].
+
+## Detailed design
+
+Change the meta data from
+```
+{meta data}
+```
+to
+```
+user1 {meta data}
+user2 {meta data}
+user3 {meta data}
+...
+```
+
+### Compatibility
+
+When upgrade from old version, all legacy meta data belongs to the default meta data space.
+```
+{meta data}
+```
+```
+default {meta data}
+user1 {meta data}
+user2 {meta data}
+...
+```
+
+## Alternatives
+
+In the multi-tenant scenario, tenant can add a {tenant-id} prefix for each data key, but tenant-id
+is a meta data esstionally, each data key has a tenant-id prefix may cost more disk space & memory
+in TiKV.

From 8ea74e248ca37205995216516a0d997977386a5e Mon Sep 17 00:00:00 2001
From: zhangjinpeng1987 <zhangjinpeng@pingcap.com>
Date: Fri, 14 Jan 2022 17:26:01 +0800
Subject: [PATCH 2/2] address comments

Signed-off-by: zhangjinpeng1987 <zhangjinpeng@pingcap.com>
---
 text/0083-multi-level-meta-space.md | 47 +++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 text/0083-multi-level-meta-space.md

diff --git a/text/0083-multi-level-meta-space.md b/text/0083-multi-level-meta-space.md
new file mode 100644
index 00000000..243b9979
--- /dev/null
+++ b/text/0083-multi-level-meta-space.md
@@ -0,0 +1,47 @@
+# Multi-level Meta Data Space
+
+## Summary
+
+PD can handle multiple users' meta data, each user only see its own meta data.
+
+## Motivation
+
+PD is the mata data center of TiKV Cluster, the meta data contains TiKV instances' addr, user data range(region)
+information, the number of replicas of data, etc.
+
+But PD currently only can handle the key space [min-key, max-key], it means that PD only can handle one user's 
+meta data, it is not possible when multiple users want share the same PD cluster as their meta system. There are
+two different scenarios that require PD can handle multiple user' meta data:
+
+1. Multiple TiKV Cluster share the same PD cluster. Because the minimal demplyment of a TiKV Cluster is 3 TiKV 3 PD,
+but it is not cost-effect if every small cluster has 3 dedicated meta data node.
+2. There are multiple tenants in the same TiKV Cluster, each tenant has it own meta data, each tenant has its own
+meta data. For example, there are multiple TiDB(tenants), each tanent has its own `gc-safepoint`, `ddl-owner-key` and 
+other meta data.
+
+## Detailed design
+
+Change the meta data from
+```
+{meta data}
+```
+to
+```
+user1 {meta data}
+user2 {meta data}
+user3 {meta data}
+...
+```
+
+### Compatibility
+
+When upgrade from old version, all legacy meta data belongs to the default meta data space.
+```
+{meta data}
+```
+```
+default {meta data}
+user1 {meta data}
+user2 {meta data}
+...
+```