Synapse Dedicated Pool

Standard

PolyBase

Connecting to Synapse

Server hosting the Synapse database is an Azure server with a URL in form of <account>.database.windows.net. No need to specify the port.

Omni Loader supports the following authentication schemes:

• SQL Server ‍This is the standard username/password combination stored in and verified by the SQL Server.

• AAD password ‍This is Azure Active Directory password authentication.

• AAD multi-factor ‍Azure Active Directory multi-factor authentication will show a pop-up authenticating you as a separate step.

• AAD integrated ‍Azure Active Directory integrated authentication is an equivalent of what was used to be called Windows authentication for SQL Server.

• AAD integrated ‍This is Azure Active Directory password authentication.

Once the server and authentication are provided, you can type your database name, or select it from the drop-down.

Connecting to the storage

Synapse can load data from Azure Blob Storage container, or from Azure Data Lake Storage Gen 2 (ADLSv2) container. We recommend ADLSv2.

Data format can be CSV or Parquet. CSV is inefficient row-based textual format, while Parquet is well-designed and fast columnar binary format. We recommend Parquet as it is significantly faster to ingest and produces smaller data files.

Both formats can be used uncompressed and compressed. One should always use the compressed format even if it means longer data preparation. Parquet can compress data up to 5 times, which directly impacts the efficiency of Synapse ingestion. While compressing terabytes of data takes time, Omni Loader is designed for efficiency and will use all CPU cores of the machine it is running on to compress the data. For further acceleration, you should use Omni Loader in a cluster mode to utilize the CPUs of several machines.

CSV can be compressed using a slow Gzip, but Parquet can use very fast Snappy compression as well. We recommend using Parquet with a Snappy compression.

Data handling defines the way Omni Loader will generate the files and clean up:

• Clear before run ‍Everything in the container folder will be deleted before the data copying starts.

• Clear after run ‍Everything in the container folder will be deleted after the data copying completes.

• Timestamped ‍Nothing is deleted. On each run, Omni Loader creates a new folder named as the current time, then place the files inside the folder. This allows for a complete history, but may generate a large amount of data after many runs.

We support three modes of storage authentication:

• Connection string ‍This is the least secure mode which should not be used in production. It requires account key and grants full access to the whole storage account.

• Managed identity ‍A secure authentication mode, leveraging AAD to grant access to the resource.

• Shared access signature ‍A good middle-ground where one can easily grant access to either a whole account or a specific container only.

The only thing left to specify is the name of the container in the storage account. Of course, if you use Shared Access Signature of a specific container, that's the name you need to specify.

Optionally, if you would like to put the data into a subfolder of the container, you can specify a subfolder name.

Caching metadata

If your Synapse source instance has a lot of tables, for example over 50 thousand, it may take a long time to execute the queries where we are reading database structure.

For this purpose, we have a special fast metadata read mode relying on the special cache tables you can build yourself if you have write access to your source database. You can execute the following script on the source (and you should re-run it when you want to refresh):

--WARNING
--WARNING - This script will DROP tables [dbo].[omniloader_cache_table_distribution] AND [dbo].[omniloader_cache_table_size]
--WARNING

SET NOCOUNT ON;
RAISERROR ('Creating table [dbo].[omniloader_cache_table_distribution]...', 0, 1) WITH NOWAIT

	IF (OBJECT_ID('dbo.omniloader_cache_table_distribution','U')) IS NOT NULL DROP TABLE dbo.omniloader_cache_table_distribution;
	CREATE TABLE dbo.omniloader_cache_table_distribution
	(
		table_schema			VARCHAR(512)	NOT NULL
	,	table_name				VARCHAR(512)	NOT NULL
	,	distribution_name		VARCHAR(512)	NULL
	,	distribution_ordinal	INT				NULL
	,	column_name				VARCHAR(512)	NULL
	)
	WITH
	(
		DISTRIBUTION = HASH(table_name)
	,	CLUSTERED INDEX (table_schema, table_name, distribution_ordinal)
	);

RAISERROR ('Table created.', 0, 1) WITH NOWAIT
RAISERROR ('Inserting data...', 0, 1) WITH NOWAIT

	INSERT INTO dbo.omniloader_cache_table_distribution
	SELECT
		s.[name]						AS table_schema
	,	t.[name]						AS table_name
	,	tdp.distribution_policy_desc	AS distribution_name
	,	cdp.distribution_ordinal		AS dist_ordinal
	,	c.[name]						AS dist_column_name
	FROM
					sys.schemas								AS s
		INNER JOIN	sys.tables								AS t	ON	t.[schema_id] = s.[schema_id]
		LEFT JOIN	sys.pdw_table_distribution_properties	AS tdp	ON	tdp.[object_id] = t.[object_id]
		LEFT JOIN	sys.pdw_column_distribution_properties	AS cdp	ON	cdp.[object_id] = tdp.[object_id]
																	AND	cdp.distribution_ordinal > 0
		LEFT JOIN	sys.columns								AS c	ON	c.[object_id] = cdp.[object_id]
																	AND	c.[column_id] = cdp.[column_id]
	WHERE 1=1;

RAISERROR ('Data inserted.', 0, 1) WITH NOWAIT
RAISERROR ('', 0, 1) WITH NOWAIT
RAISERROR ('Creating table [dbo].[omniloader_cache_table_size]...', 0, 1) WITH NOWAIT

	IF (OBJECT_ID('dbo.omniloader_cache_table_size','U')) IS NOT NULL DROP TABLE dbo.omniloader_cache_table_size;
	CREATE TABLE dbo.omniloader_cache_table_size
	(
		table_schema		VARCHAR(512)	NOT NULL
	,	table_name			VARCHAR(512)	NOT NULL
	,	partition_number	INT				NULL
	,	record_count		BIGINT			NULL
	,	byte_count			BIGINT			NULL
	)
	WITH
	(
		DISTRIBUTION = HASH(table_name)
	,	CLUSTERED INDEX (table_name, table_schema)
	);

RAISERROR ('Table created.', 0, 1) WITH NOWAIT
RAISERROR ('Inserting data...', 0, 1) WITH NOWAIT

	INSERT INTO dbo.omniloader_cache_table_size
	SELECT
		s.[name]									AS table_schema
	,	t.[name]									AS table_name
	,	nps.partition_number						AS partition_number
	,	SUM(nps.row_count)							AS record_count
	,	SUM(	nps.in_row_data_page_count
			+	nps.row_overflow_used_page_count
			+	nps.lob_used_page_count) * 8 * 1024	AS byte_count
	FROM
					sys.schemas							AS s
		INNER JOIN	sys.tables							AS t	ON	t.[schema_id] = s.[schema_id]
		LEFT JOIN	sys.indexes							AS i	ON	i.[object_id] = t.[object_id]
																AND	i.index_id <= 1
		LEFT JOIN	sys.pdw_table_mappings				AS tm	ON	tm.[object_id] = t.[object_id]
		LEFT JOIN	sys.pdw_nodes_tables				AS nt	ON	nt.[name] = tm.physical_name
		LEFT JOIN	sys.dm_pdw_nodes					AS pn	ON	pn.pdw_node_id = nt.pdw_node_id
																AND pn.[type] = 'COMPUTE'
		LEFT JOIN	sys.dm_pdw_nodes_db_partition_stats	AS nps	ON	nps.[object_id] = nt.[object_id]
																AND	nps.pdw_node_id = nt.pdw_node_id
																AND	nps.distribution_id = nt.distribution_id
	WHERE 1=1
	GROUP BY
		s.[name]
	,	t.[name]
	,	nps.partition_number;

RAISERROR ('Data inserted.', 0, 1) WITH NOWAIT
RAISERROR ('', 0, 1) WITH NOWAIT