add timestamp to global state table for lease table cleanup

docs/BindingsOverview.md

@@ -22,6 +22,7 @@
       - [Startup retries](#startup-retries)
       - [Broken connection retries](#broken-connection-retries)
       - [Function exception retries](#function-exception-retries)
+      - [Lease Tables clean up](#lease-tables-clean-up)
 
 ## Input Binding
 
@@ -147,7 +148,7 @@ If an exception occurs in the user function when processing changes then the bat
 
 If the function execution fails 5 times in a row for a given row then that row is completely ignored for all future changes. Because the rows in a batch are not deterministic, rows in a failed batch may end up in different batches in subsequent invocations. This means that not all rows in the failed batch will necessarily be ignored. If other rows in the batch were the ones causing the exception, the "good" rows may end up in a different batch that doesn't fail in future invocations.
 
-You can run this query to see what rows have failed 5 times and are currently ignored, see [Leases table](#az_funcleases_) documentation for how to get the correct Leases table to query for your function.
+You can run this query to see what rows have failed 5 times and are currently ignored, see [Leases table](./TriggerBinding.md#az_funcleases_) documentation for how to get the correct Leases table to query for your function.
 
 ```sql
 SELECT * FROM [az_func].[Leases_<FunctionId>_<TableId>] WHERE _az_func_AttemptCount = 5
@@ -168,3 +169,93 @@ e.g.
 ```sql
 UPDATE [Products].[az_func].[Leases_<FunctionId>_<TableId>] SET _az_func_AttemptCount = 0 WHERE ProductId = 123
 ```
+
+#### Lease Tables clean up
+
+Before clean up, please see [Leases table](./TriggerBinding.md#az_funcleases_) documentation for understanding how they are created and used.
+
+Why clean up?
+1. You renamed your function/class/method name and a new lease table is created making the old one obsolete for clean up.
+2. You have created multiple trigger functions that are obsolete which have associated tables that require cleaning up.
+3. You want to reset your environment and start afresh.
+There are many a reason that require cleaning to maintain our databases and since we currently don't handle that within the extension, below are some scripts that guide you through cleaning the leases table without them filling up the database.
+
+- Deletes all the lease tables that haven't been accessed in N days:
+
+```sql
+-- Deletes all the lease tables that haven't been accesses in ? days(represented by @CleanupAgeDays variable and needs to defined before running the query).
+-- And removes them from the GlobalState table.
+USE <Insert DATABASE name here>;
+DECLARE @TableName NVARCHAR(MAX);
+DECLARE @UserFunctionId char(16);
+DECLARE @UserTableId int;
+DECLARE @CleanupAgeDays int = <Insert desired cleanup age in days here>;
+DECLARE LeaseTable_Cursor CURSOR FOR
+
+SELECT 'az_func.Leases_'+UserFunctionId+'_'+convert(varchar(100),UserTableID) as TABLE_NAME, UserFunctionID, UserTableID
+FROM az_func.GlobalState
+WHERE DATEDIFF(day, LastAccessTime, GETDATE()) > @CleanupAgeDays
+
+OPEN LeaseTable_Cursor;
+
+FETCH NEXT FROM LeaseTable_Cursor INTO @TableName, @UserFunctionId, @UserTableId;
+
+WHILE @@FETCH_STATUS = 0
+BEGIN
+    EXEC ('DROP TABLE IF EXISTS ' + @TableName);
+    DELETE FROM az_func.GlobalState WHERE UserFunctionID = @UserFunctionId and UserTableID = @UserTableId
+    FETCH NEXT FROM LeaseTable_Cursor INTO @TableName, @UserFunctionId, @UserTableId;
+END;
+
+CLOSE LeaseTable_Cursor;
+
+DEALLOCATE LeaseTable_Cursor;
+```
+
+- Clean up a specific lease table concerning a specific function:
+
+To find the name of the leases table associated with your function, look in the log output for a line such as this which is emitted when the trigger is started.
+
+`SQL trigger Leases table: [az_func].[Leases_84d975fca0f7441a_901578250]`
+
+This log message is at the `Information` level, so make sure your log level is set correctly.
+
+```sql
+-- Deletes the specified lease table and removes it from GlobalState table.
+USE <Insert DATABASE name here>;
+DECLARE @TableName NVARCHAR(MAX) = <Insert lease table name here>; -- e.g. '[az_func].[Leases_84d975fca0f7441a_901578250]
+DECLARE @UserFunctionId char(16) = <Insert function ID here>; -- e.g. '84d975fca0f7441a'
+DECLARE @UserTableId int = <Insert table ID here>; -- e.g. '901578250'
+
+DROP TABLE IF EXISTS @TableName
+DELETE FROM az_func.GlobalState WHERE UserFunctionID = @UserFunctionId and UserTableID = @UserTableId
+```
+
+- Clear all trigger related data for a reset:
+
+```sql
+-- Deletes all the lease tables and clears them from the GlobalState table.
+USE <Insert DATABASE name here>;
+DECLARE @TableName NVARCHAR(MAX);
+DECLARE @UserFunctionId char(16);
+DECLARE @UserTableId int;
+DECLARE LeaseTable_Cursor CURSOR FOR
+
+SELECT 'az_func.Leases_'+UserFunctionId+'_'+convert(varchar(100),UserTableID) as TABLE_NAME, UserFunctionID, UserTableID
+FROM az_func.GlobalState
+
+OPEN LeaseTable_Cursor;
+
+FETCH NEXT FROM LeaseTable_Cursor INTO @TableName, @UserFunctionId, @UserTableId;
+
+WHILE @@FETCH_STATUS = 0
+BEGIN
+    EXEC ('DROP TABLE IF EXISTS ' + @TableName);
+    DELETE FROM az_func.GlobalState WHERE UserFunctionID = @UserFunctionId and UserTableID = @UserTableId
+    FETCH NEXT FROM LeaseTable_Cursor INTO @TableName, @UserFunctionId, @UserTableId;
+END;
+
+CLOSE LeaseTable_Cursor;
+
+DEALLOCATE LeaseTable_Cursor;
+```

src/TriggerBinding/SqlTableChangeMonitor.cs

@@ -955,7 +955,7 @@ LEFT OUTER JOIN {this._leasesTableName} AS l ON {leasesTableJoinCondition}
                 IF @unprocessed_changes = 0 AND @current_last_sync_version < {newLastSyncVersion}
                 BEGIN
                     UPDATE {GlobalStateTableName}
-                    SET LastSyncVersion = {newLastSyncVersion}
+                    SET LastSyncVersion = {newLastSyncVersion}, LastAccessTime = GETDATE()
                     WHERE UserFunctionID = '{this._userFunctionId}' AND UserTableID = {this._userTableId};
 
                     DELETE FROM {this._leasesTableName} WHERE {LeasesTableChangeVersionColumnName} <= {newLastSyncVersion};

src/TriggerBinding/SqlTriggerListener.cs

@@ -321,8 +321,12 @@ IF OBJECT_ID(N'{GlobalStateTableName}', 'U') IS NULL
                         UserFunctionID char(16) NOT NULL,
                         UserTableID int NOT NULL,
                         LastSyncVersion bigint NOT NULL,
+                        LastAccessTime Datetime NULL,
                         PRIMARY KEY (UserFunctionID, UserTableID)
                     );
+                ELSE IF NOT EXISTS(SELECT 1 FROM sys.columns WHERE Name = N'LastAccessTime'
+                    AND Object_ID = Object_ID(N'{GlobalStateTableName}'))
+                        ALTER TABLE {GlobalStateTableName} ADD LastAccessTime Datetime NULL;
             ";
 
             using (var createGlobalStateTableCommand = new SqlCommand(createGlobalStateTableQuery, connection, transaction))