Enable read committed snapshot on template database (#932)

Author: SimonCropp

pages/design.md

@@ -44,6 +44,17 @@ The usual approach for consuming the API in a test project is as follows.
 
 This assumes that there is a schema and data (and DbContext in the EntityFramework context) used for all tests. If those caveats are not correct then multiple SqlInstances can be used.
 
+
+## Template database settings
+
+When the template is built, a few database-level settings are applied. These persist in the template's `.mdf`/`.ldf` files and are inherited by every database attached from the template.
+
+ * `auto_update_statistics off` — avoids background statistics updates causing nondeterministic test timing.
+ * `read_committed_snapshot on` — `READ COMMITTED` uses row versioning instead of shared locks. Required to prevent S/X-lock deadlocks between parallel `[SharedDbWithTransaction]` tests against the same shared database.
+
+If the template files already exist on disk from a previous build, these settings are not reapplied — the template needs to be regenerated (delete the template files, or change the timestamp passed to `SqlInstance`) for new settings to take effect.
+
+
 More information:
 
  * [Raw SqlConnection Usage](/pages/raw-usage.md)

pages/ef-usage.md

@@ -292,7 +292,7 @@ public async Task SharedDatabase()
     AreEqual(0, count);
 }
 ```
-<sup><a href='/src/EfLocalDb.Tests/Tests.cs#L674-L684' title='Snippet source file'>snippet source</a> | <a href='#snippet-EfSharedDatabase' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/EfLocalDb.Tests/Tests.cs#L687-L697' title='Snippet source file'>snippet source</a> | <a href='#snippet-EfSharedDatabase' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 Pass `useTransaction: true` to get an auto-rolling-back transaction, allowing writes without affecting other tests.
@@ -318,7 +318,7 @@ public async Task SharedDatabase_WithTransaction()
     AreEqual(0, count);
 }
 ```
-<sup><a href='/src/EfLocalDb.Tests/Tests.cs#L698-L716' title='Snippet source file'>snippet source</a> | <a href='#snippet-EfSharedDatabase_WithTransaction' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/EfLocalDb.Tests/Tests.cs#L711-L729' title='Snippet source file'>snippet source</a> | <a href='#snippet-EfSharedDatabase_WithTransaction' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 

pages/mdsource/design.source.md

@@ -37,6 +37,17 @@ The usual approach for consuming the API in a test project is as follows.
 
 This assumes that there is a schema and data (and DbContext in the EntityFramework context) used for all tests. If those caveats are not correct then multiple SqlInstances can be used.
 
+
+## Template database settings
+
+When the template is built, a few database-level settings are applied. These persist in the template's `.mdf`/`.ldf` files and are inherited by every database attached from the template.
+
+ * `auto_update_statistics off` — avoids background statistics updates causing nondeterministic test timing.
+ * `read_committed_snapshot on` — `READ COMMITTED` uses row versioning instead of shared locks. Required to prevent S/X-lock deadlocks between parallel `[SharedDbWithTransaction]` tests against the same shared database.
+
+If the template files already exist on disk from a previous build, these settings are not reapplied — the template needs to be regenerated (delete the template files, or change the timestamp passed to `SqlInstance`) for new settings to take effect.
+
+
 More information:
 
  * [Raw SqlConnection Usage](/pages/raw-usage.md)

pages/template-database-size.md

@@ -21,7 +21,7 @@ To have a smaller file size [DBCC SHRINKFILE](https://docs.microsoft.com/en-us/s
 use model;
 dbcc shrinkfile(modeldev, {size})
 ```
-<sup><a href='/src/LocalDb/SqlBuilder.cs#L70-L73' title='Snippet source file'>snippet source</a> | <a href='#snippet-ShrinkModelDb' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/LocalDb/SqlBuilder.cs#L84-L87' title='Snippet source file'>snippet source</a> | <a href='#snippet-ShrinkModelDb' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 

src/EfLocalDb.Tests/Tests.cs

@@ -78,6 +78,19 @@ await ThrowsTask(() => database.SaveChangesAsync())
             .IgnoreStackTrace();
     }
 
+    [Test]
+    public async Task TemplateHasReadCommittedSnapshot()
+    {
+        // Guards against accidental removal of the ALTER DATABASE statement that enables
+        // READ_COMMITTED_SNAPSHOT on the template — required to avoid S/X-lock deadlocks
+        // between parallel [SharedDbWithTransaction] tests on the same shared database.
+        await using var database = await instance.Build();
+        await using var command = database.Connection.CreateCommand();
+        command.CommandText = "select is_read_committed_snapshot_on from sys.databases where name = db_name()";
+        var enabled = (bool) (await command.ExecuteScalarAsync())!;
+        True(enabled);
+    }
+
     [Test]
     public async Task RemoveData()
     {

src/LocalDb/SqlBuilder.cs

@@ -50,6 +50,20 @@ create database [template] on
         execute sp_detach_db N'template', 'true';
         """;
 
+    // Database-level settings applied to the template before detach. Persisted in the
+    // .mdf/.ldf files, so every database attached from the template inherits them.
+    //   auto_update_statistics off  - avoids background stats updates causing
+    //                                 nondeterministic test timing.
+    //   read_committed_snapshot on  - READ COMMITTED uses row versioning instead of
+    //                                 shared locks, preventing S/X-lock deadlocks
+    //                                 between parallel [SharedDbWithTransaction] tests
+    //                                 against the same shared database.
+    public static string TemplateSettingsCommand =
+        """
+        alter database [template] set auto_update_statistics off;
+        alter database [template] set read_committed_snapshot on;
+        """;
+
     public static string DetachAndShrinkTemplateCommand =
         """
         use [template];

src/LocalDb/SqlExtensions.cs

@@ -1,8 +1,8 @@
 static class SqlExtensions
 {
-    public static async Task ExecuteCommandAsync(this SqlConnection connection, string commandText)
+    public static async Task ExecuteCommandAsync(this SqlConnection connection, params string[] commandTexts)
     {
-        commandText = commandText.Trim();
+        var commandText = string.Join('\n', commandTexts).Trim();
 
         try
         {

src/LocalDb/Wrapper.cs

@@ -260,10 +260,10 @@ async Task CreateAndDetachTemplate(
                     await connection.ExecuteCommandAsync("checkpoint");
                 }
 
-                await masterConnection.ExecuteCommandAsync("alter database [template] set auto_update_statistics off");
-
-                // Detach the template database after callback completes
-                await masterConnection.ExecuteCommandAsync(SqlBuilder.DetachTemplateCommand);
+                // Apply template settings then detach in a single batch.
+                await masterConnection.ExecuteCommandAsync(
+                    SqlBuilder.TemplateSettingsCommand,
+                    SqlBuilder.DetachTemplateCommand);
             }
         }
     }
@@ -299,8 +299,9 @@ async Task Rebuild(DateTime timestamp, Func<SqlConnection, Task> buildTemplate,
             await connection.ExecuteCommandAsync("checkpoint");
         }
 
-        await masterConnection.ExecuteCommandAsync("alter database [template] set auto_update_statistics off");
-        await masterConnection.ExecuteCommandAsync(SqlBuilder.DetachAndShrinkTemplateCommand);
+        await masterConnection.ExecuteCommandAsync(
+            SqlBuilder.TemplateSettingsCommand,
+            SqlBuilder.DetachAndShrinkTemplateCommand);
 
         File.SetCreationTime(DataFile, timestamp);
     }