Reduce IsAzureSynapseOnDemandEndpoint allocations

[vonzshik]

Every time you create a new instance of SqlConnection, if the connection string's RetryCount is equal to 1 (which is the default value) SqlClient will attempt to subtly replace it with 5 if it determines that the host is azure synapse on demand endpoint.

SqlClient/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlConnection.cs

Lines 423 to 429 in 6d2473d

	_connectRetryCount = connString.ConnectRetryCount;
	// For Azure Synapse ondemand connections, set _connectRetryCount to 5 instead of 1 to greatly improve recovery
	// success rate. Note: Synapse should be detected first as it could be detected as a regular Azure SQL DB endpoint.
	if (_connectRetryCount == 1 && ADP.IsAzureSynapseOnDemandEndpoint(connString.DataSource))
	{
	_connectRetryCount = 5;
	}

The problem is that to determine that SqlClient concats prefix -ondemand with a collection of specific endpoints and then checks whether the host contains any endpoint. With 5 endpoints, that's 5 string allocations per each instance of SqlConnection, which in a simple benchmark results in about 40% of total allocations.

SqlClient/src/Microsoft.Data.SqlClient/src/Microsoft/Data/Common/AdapterUtil.cs

Lines 821 to 832 in 6d2473d

	// check if servername ends with any endpoints
	for (int index = 0; index < s_azureSqlServerEndpoints.Length; index++)
	{
	string endpoint = string.IsNullOrEmpty(prefix) ? s_azureSqlServerEndpoints[index] : prefix + s_azureSqlServerEndpoints[index];
	if (length > endpoint.Length)
	{
	if (string.Compare(dataSource, length - endpoint.Length, endpoint, 0, endpoint.Length, StringComparison.OrdinalIgnoreCase) == 0)
	{
	return true;
	}
	}
	}

Maybe it's better to instantiate them once just like it's done for azure sql server endpoints?

[vonzshik]

@ErikEJ more like making a copy of s_azureSqlServerEndpoints with each endpoint having ONDEMAND_PREFIX prepended and passing a specific array to IsEndpoint instead of allocating a string per each.

SqlClient-azure-synapse-check.patch

[ErikEJ]

@vonzshik Got it!

[ErikEJ]

@vonzshik Planning to do a PR?

[vonzshik]

Not really, so go on ahead.