/// <summary>
/// Constructs cached representation of a mapping object.
/// </summary>
/// <param name="storeMapping">Storage representation of mapping.</param>
/// <param name="timeToLiveMilliseconds">Mapping expiration time.</param>
internal CacheMapping(IStoreMapping storeMapping, long timeToLiveMilliseconds)
{
this.Mapping = storeMapping;
this.CreationTime = TimerUtils.GetTimestamp();
this.TimeToLiveMilliseconds = timeToLiveMilliseconds;
}
/// <summary>
/// Whether TimeToLiveMilliseconds have elapsed
/// since the CreationTime
/// </summary>
/// <returns>True if they have</returns>
public bool HasTimeToLiveExpired()
{
return(TimerUtils.ElapsedMillisecondsSince(this.CreationTime) >= this.TimeToLiveMilliseconds);
}
/// <summary>
/// Given a key value, obtains a SqlConnection to the shard in the mapping
/// that contains the key value.
/// </summary>
/// <typeparam name="TMapping">Mapping type.</typeparam>
/// <typeparam name="TKey">Key type.</typeparam>
/// <param name="key">Input key value.</param>
/// <param name="constructMapping">Delegate to construct a mapping object.</param>
/// <param name="errorCategory">Error category.</param>
/// <param name="connectionString">
/// Connection string with credential information, the DataSource and Database are
/// obtained from the results of the lookup operation for key.
/// </param>
/// <param name="options">Options for validation operations to perform on opened connection.</param>
/// <returns>An opened SqlConnection.</returns>
protected SqlConnection OpenConnectionForKey <TMapping, TKey>(
TKey key,
Func <ShardMapManager, ShardMap, IStoreMapping, TMapping> constructMapping,
ShardManagementErrorCategory errorCategory,
string connectionString,
ConnectionOptions options = ConnectionOptions.Validate) where TMapping : class, IShardProvider
{
ShardKey sk = new ShardKey(ShardKey.ShardKeyTypeFromType(typeof(TKey)), key);
// Try to find the mapping within the cache.
ICacheStoreMapping csm = this.Manager.Cache.LookupMappingByKey(this.ShardMap.StoreShardMap, sk);
IStoreMapping sm;
if (csm != null)
{
sm = csm.Mapping;
}
else
{
sm = this.LookupMappingForOpenConnectionForKey(
sk,
CacheStoreMappingUpdatePolicy.OverwriteExisting,
errorCategory);
}
SqlConnection result;
try
{
// Initially attempt to connect based on lookup results from either cache or GSM.
result = this.ShardMap.OpenConnection(
constructMapping(this.Manager, this.ShardMap, sm),
connectionString,
options);
// Reset TTL on successful connection.
if (csm != null && csm.TimeToLiveMilliseconds > 0)
{
csm.ResetTimeToLive();
}
//this.Manager.Cache.IncrementPerformanceCounter(this.ShardMap.StoreShardMap, PerformanceCounterName.DdrOperationsPerSec);
return(result);
}
catch (ShardManagementException smme)
{
// If we hit a validation failure due to stale version of mapping, we will perform one more attempt.
if (((options & ConnectionOptions.Validate) == ConnectionOptions.Validate) &&
smme.ErrorCategory == ShardManagementErrorCategory.Validation &&
smme.ErrorCode == ShardManagementErrorCode.MappingDoesNotExist)
{
// Assumption here is that this time the attempt should succeed since the cache entry
// has already been either evicted, or updated based on latest data from the server.
sm = this.LookupMappingForOpenConnectionForKey(
sk,
CacheStoreMappingUpdatePolicy.OverwriteExisting,
errorCategory);
result = this.ShardMap.OpenConnection(
constructMapping(this.Manager, this.ShardMap, sm),
connectionString,
options);
//this.Manager.Cache.IncrementPerformanceCounter(this.ShardMap.StoreShardMap, PerformanceCounterName.DdrOperationsPerSec);
return(result);
}
else
{
// The error was not due to validation but something else e.g.
// 1) Shard map does not exist
// 2) Mapping could not be found.
throw;
}
}
catch (SqlException)
{
// We failed to connect. If we were trying to connect from an entry in cache and mapping expired in cache.
if (csm != null && TimerUtils.ElapsedMillisecondsSince(csm.CreationTime) >= csm.TimeToLiveMilliseconds)
{
using (IdLock _idLock = new IdLock(csm.Mapping.StoreShard.Id))
{
// Similar to DCL pattern, we need to refresh the mapping again to see if we still need to go to the store
// to lookup the mapping after acquiring the shard lock. It might be the case that a fresh version has already
// been obtained by some other thread.
csm = this.Manager.Cache.LookupMappingByKey(this.ShardMap.StoreShardMap, sk);
// Only go to store if the mapping is stale even after refresh.
if (csm == null || TimerUtils.ElapsedMillisecondsSince(csm.CreationTime) >= csm.TimeToLiveMilliseconds)
{
// Refresh the mapping in cache. And try to open the connection after refresh.
sm = this.LookupMappingForOpenConnectionForKey(
sk,
CacheStoreMappingUpdatePolicy.UpdateTimeToLive,
errorCategory);
}
else
{
sm = csm.Mapping;
}
}
result = this.ShardMap.OpenConnection(
constructMapping(this.Manager, this.ShardMap, sm),
connectionString,
options);
// Reset TTL on successful connection.
if (csm != null && csm.TimeToLiveMilliseconds > 0)
{
csm.ResetTimeToLive();
}
//this.Manager.Cache.IncrementPerformanceCounter(this.ShardMap.StoreShardMap, PerformanceCounterName.DdrOperationsPerSec);
return(result);
}
else
{
// Either:
// 1) The mapping is still within the TTL. No refresh.
// 2) Mapping was not in cache, we originally did a lookup for mapping in GSM and even then could not connect.
throw;
}
}
}
