/// <summary>
/// Creates a new shard, or gets an existing empty shard (i.e. a shard that has no mappings).
/// The reason why an empty shard might exist is that it was created and initialized but we
/// failed to create a mapping to it.
/// </summary>
private static Shard CreateOrGetEmptyShard(RangeShardMap <int> shardMap)
{
// Get an empty shard if one already exists, otherwise create a new one
Shard shard = FindEmptyShard(shardMap);
if (shard == null)
{
// No empty shard exists, so create one
// Choose the shard name
string databaseName = string.Format(ShardNameFormat, shardMap.GetShards().Count());
// Only create the database if it doesn't already exist. It might already exist if
// we tried to create it previously but hit a transient fault.
if (!SqlDatabaseUtils.DatabaseExists(Configuration.ShardMapManagerServerName, databaseName))
{
SqlDatabaseUtils.CreateDatabase(Configuration.ShardMapManagerServerName, databaseName);
}
// Create schema and populate reference data on that database
// The initialize script must be idempotent, in case it was already run on this database
// and we failed to add it to the shard map previously
SqlDatabaseUtils.ExecuteSqlScript(
Configuration.ShardMapManagerServerName, databaseName, InitializeShardScriptFile);
// Add it to the shard map
ShardLocation shardLocation = new ShardLocation(Configuration.ShardMapManagerServerName, databaseName);
shard = ShardManagementUtils.CreateOrGetShard(shardMap, shardLocation);
}
return(shard);
}
/// <summary>
/// Tries to get the ShardMapManager that is stored in the specified database.
/// </summary>
public static ShardMapManager TryGetShardMapManager(string shardMapManagerServerName, string shardMapManagerDatabaseName)
{
string shardMapManagerConnectionString =
Configuration.GetConnectionString(
Configuration.ShardMapManagerServerName,
Configuration.ShardMapManagerDatabaseName);
if (!SqlDatabaseUtils.DatabaseExists(shardMapManagerServerName, shardMapManagerDatabaseName))
{
// Shard Map Manager database has not yet been created
return(null);
}
ShardMapManager shardMapManager;
bool smmExists = ShardMapManagerFactory.TryGetSqlShardMapManager(
shardMapManagerConnectionString,
ShardMapManagerLoadPolicy.Lazy,
out shardMapManager);
if (!smmExists)
{
// Shard Map Manager database exists, but Shard Map Manager has not been created
return(null);
}
return(shardMapManager);
}
/// <summary>
/// Drops all shards and the shard map manager database (if it exists).
/// </summary>
private static void DropAll()
{
ListShardMap <int> shardMap = TryGetShardMap();
if (shardMap != null)
{
// Drop shards
foreach (Shard shard in shardMap.GetShards())
{
SqlDatabaseUtils.DropDatabase(shard.Location.DataSource, shard.Location.Database);
}
}
if (SqlDatabaseUtils.DatabaseExists(Configuration.ShardMapManagerServerName, Configuration.ShardMapManagerDatabaseName))
{
// Drop shard map manager database
SqlDatabaseUtils.DropDatabase(Configuration.ShardMapManagerServerName, Configuration.ShardMapManagerDatabaseName);
}
// Since we just dropped the shard map manager database, this shardMapManager reference is now non-functional.
// So set it to null so that the program knows that the shard map manager is gone.
s_shardMapManager = null;
}
/// <summary>
/// Creates a shard map manager, creates a shard map, and creates a shard
/// with a mapping for the full range of 32-bit integers.
/// </summary>
private static void CreateShardMapManagerAndShard()
{
if (s_shardMapManager != null)
{
ConsoleUtils.WriteWarning("Shard Map Manager already exists");
return;
}
// Create shard map manager database
if (!SqlDatabaseUtils.DatabaseExists(Configuration.ShardMapManagerServerName, Configuration.ShardMapManagerDatabaseName))
{
SqlDatabaseUtils.CreateDatabase(Configuration.ShardMapManagerServerName, Configuration.ShardMapManagerDatabaseName);
}
// Create shard map manager
string shardMapManagerConnectionString =
Configuration.GetConnectionString(
Configuration.ShardMapManagerServerName,
Configuration.ShardMapManagerDatabaseName);
s_shardMapManager = ShardManagementUtils.CreateOrGetShardMapManager(shardMapManagerConnectionString);
// Create shard map
ListShardMap <int> shardMap = ShardManagementUtils.CreateOrGetRangeShardMap <int>(
s_shardMapManager, Configuration.ShardMapName);
// Create schema info so that the split-merge service can be used to move data in sharded tables
// and reference tables.
CreateSchemaInfo(shardMap.Name);
// If there are no shards, add two shards: one for [0,100) and one for [100,+inf)
if (!shardMap.GetShards().Any())
{
CreateShardSample.CreateShard(shardMap, 1);
CreateShardSample.CreateShard(shardMap, 2);
}
}