From 7b2ca4eba9336a844154424c005ec670f0707b67 Mon Sep 17 00:00:00 2001
From: Jacek Laskowski <jacek@japila.pl>
Date: Fri, 18 Oct 2024 12:39:26 +0200
Subject: [PATCH] MetastoreRepository

---
 .../persistent-storage/MetastoreRepository.md | 89 ++++++++++++++++++-
 1 file changed, 88 insertions(+), 1 deletion(-)

diff --git a/docs/persistent-storage/MetastoreRepository.md b/docs/persistent-storage/MetastoreRepository.md
index d91a8a6..6ddb68c 100644
--- a/docs/persistent-storage/MetastoreRepository.md
+++ b/docs/persistent-storage/MetastoreRepository.md
@@ -1,3 +1,90 @@
 # MetastoreRepository
 
-`MetastoreRepository` is...FIXME
+## Init Metastore If Needed { #initMetastoreIfNeeded }
+
+```java
+MetastoreDAO initMetastoreIfNeeded()
+```
+
+`initMetastoreIfNeeded` starts a transaction (with a new `Session` (Hibernate) from the system-wide [SessionFactory](HibernateUtils.md#SESSION_FACTORY)).
+
+`initMetastoreIfNeeded` [looks up the one and only metastore](#getMetastoreDAO).
+
+Unless found, `initMetastoreIfNeeded` creates a new metastore.
+
+`initMetastoreIfNeeded` prints out the following INFO message to the logs:
+
+```text
+No metastore found, initializing a metastore for the server...
+```
+
+`initMetastoreIfNeeded` creates a `MetastoreDAO` with a pseudo-randomly generated UUID and persists it.
+
+`initMetastoreIfNeeded` prints out the following INFO message to the logs:
+
+```text
+Server initialized with metastore id: [id]
+```
+
+---
+
+In case of any exception, `initMetastoreIfNeeded` prints out the following ERROR message to the logs:
+
+```text
+Failed to initialize metastore
+```
+
+---
+
+`initMetastoreIfNeeded` is used when:
+
+* `UnityCatalogServer` is requested to [start](../server/UnityCatalogServer.md#start)
+
+## System-Wide MetastoreRepository Instance { #INSTANCE }
+
+```java
+MetastoreRepository INSTANCE
+```
+
+`MetastoreRepository` creates an instance of itself at the class load time.
+
+??? note "Final Property"
+    `INSTANCE` is a Java **final property** to prevent [subclasses](#implementations) from overriding or hiding it.
+
+    Learn more in the [Java Language Specification]({{ java.spec }}/jls-8.html#jls-8.4.3.3).
+
+??? note "Static Property"
+    `INSTANCE` is a Java **class property** to be invoked without a reference to a particular object.
+
+    Learn more in the [Java Language Specification]({{ java.spec }}/jls-8.html#jls-8.4.3.2).
+
+This `MetastoreRepository` instance is available using [MetastoreRepository.getInstance](#getInstance).
+
+### Get Instance { #getInstance }
+
+```java
+MetastoreRepository getInstance()
+```
+
+??? note "Static Method"
+    `getInstance` is a Java **class method** to be invoked without a reference to a particular object.
+
+    Learn more in the [Java Language Specification]({{ java.spec }}/jls-8.html#jls-8.4.3.2).
+
+`getInstance` returns the [system-wide MetastoreRepository Instance](#INSTANCE).
+
+---
+
+`getInstance` is used when:
+
+* `UnityCatalogServer` is requested to [start](../server/UnityCatalogServer.md#start)
+* `KeyMapperUtil` is requested to [mapResourceKeys](../server-authorization/KeyMapperUtil.md#mapResourceKeys)
+* `UnityAccessUtil` is requested for the [MetastoreRepository](../server-authorization/UnityAccessUtil.md#METASTORE_REPOSITORY)
+* `CatalogService` is requested to [filterCatalogs](../server/CatalogService.md#filterCatalogs)
+* `FunctionService` is requested to [filterFunctions](../server/FunctionService.md#filterFunctions)
+* `MetastoreService` is requested for the [MetastoreRepository](../server/MetastoreService.md#METASTORE_REPOSITORY)
+* `ModelService` is requested to [filterModels](../server/ModelService.md#filterModels)
+* `PermissionService` is requested for the [MetastoreRepository](../server/PermissionService.md#METASTORE_REPOSITORY)
+* `SchemaService` is requested to [filterSchemas](../server/SchemaService.md#filterSchemas)
+* `TableService` is requested to [filterTables](../server/TableService.md#filterTables)
+* `VolumeService` is requested to [filterVolumes](../server/VolumeService.md#filterVolumes)