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Design and performance for Netezza migrations

  • Artikkeli

This article is part one of a seven-part series that provides guidance on how to migrate from Netezza to Azure Synapse Analytics. The focus of this article is best practices for design and performance.

Overview

Due to end of support from IBM, many existing users of Netezza data warehouse systems want to take advantage of the innovations provided by modern cloud environments. Infrastructure-as-a-service (IaaS) and platform-as-a-service (PaaS) cloud environments let you delegate tasks like infrastructure maintenance and platform development to the cloud provider.

Tip

More than just a database—the Azure environment includes a comprehensive set of capabilities and tools.

Although Netezza and Azure Synapse Analytics are both SQL databases that use massively parallel processing (MPP) techniques to achieve high query performance on exceptionally large data volumes, there are some basic differences in approach:

  • Legacy Netezza systems are often installed on-premises and use proprietary hardware, while Azure Synapse is cloud-based and uses Azure storage and compute resources.

  • Upgrading a Netezza configuration is a major task involving extra physical hardware and potentially lengthy database reconfiguration, or dump and reload. Because storage and compute resources are separate in the Azure environment and have elastic scaling capability, those resources can be scaled upwards or downwards independently.

  • You can pause or resize Azure Synapse as needed to reduce resource utilization and cost.

Microsoft Azure is a globally available, highly secure, scalable cloud environment that includes Azure Synapse and an ecosystem of supporting tools and capabilities. The next diagram summarizes the Azure Synapse ecosystem.

Chart showing the Azure Synapse ecosystem of supporting tools and capabilities.

Azure Synapse provides best-of-breed relational database performance by using techniques such as MPP and multiple levels of automated caching for frequently used data. You can see the results of these techniques in independent benchmarks such as the one run recently by GigaOm, which compares Azure Synapse to other popular cloud data warehouse offerings. Customers who migrate to the Azure Synapse environment see many benefits, including:

  • Improved performance and price/performance.

  • Increased agility and shorter time to value.

  • Faster server deployment and application development.

  • Elastic scalability—only pay for actual usage.

  • Improved security/compliance.

  • Reduced storage and disaster recovery costs.

  • Lower overall TCO, better cost control, and streamlined operational expenditure (OPEX).

To maximize these benefits, migrate new or existing data and applications to the Azure Synapse platform. In many organizations, migration includes moving an existing data warehouse from a legacy on-premises platform, such as Netezza, to Azure Synapse. At a high level, the migration process includes these steps:

    Preparation                     🡆

  • Define scope—what is to be migrated.

  • Build inventory of data and processes for migration.

  • Define data model changes (if any).

  • Define source data extract mechanism.

  • Identify the appropriate Azure and third-party tools and features to be used.

  • Train staff early on the new platform.

  • Set up the Azure target platform.

    Migration                     🡆

  • Start small and simple.

  • Automate wherever possible.

  • Leverage Azure built-in tools and features to reduce migration effort.

  • Migrate metadata for tables and views.

  • Migrate historical data to be maintained.

  • Migrate or refactor stored procedures and business processes.

  • Migrate or refactor ETL/ELT incremental load processes.

    Post migration

  • Monitor and document all stages of the process.

  • Use the experience gained to build a template for future migrations.

  • Re-engineer the data model if required (using new platform performance and scalability).

  • Test applications and query tools.

  • Benchmark and optimize query performance.

This article provides general information and guidelines for performance optimization when migrating a data warehouse from an existing Netezza environment to Azure Synapse. The goal of performance optimization is to achieve the same or better data warehouse performance in Azure Synapse after schema migration.

Design considerations

Migration scope

When you're preparing to migrate from a Netezza environment, consider the following migration choices.

Choose the workload for the initial migration

Typically, legacy Netezza environments have evolved over time to encompass multiple subject areas and mixed workloads. When you're deciding where to start on a migration project, choose an area where you'll be able to:

  • Prove the viability of migrating to Azure Synapse by quickly delivering the benefits of the new environment.

  • Allow your in-house technical staff to gain relevant experience with the processes and tools that they'll use when they migrate other areas.

  • Create a template for further migrations that's specific to the source Netezza environment and the current tools and processes that are already in place.

A good candidate for an initial migration from a Netezza environment supports the preceding items, and:

  • Implements a BI/Analytics workload rather than an online transaction processing (OLTP) workload.

  • Has a data model, such as a star or snowflake schema, that can be migrated with minimal modification.

Tip

Create an inventory of objects that need to be migrated, and document the migration process.

The volume of migrated data in an initial migration should be large enough to demonstrate the capabilities and benefits of the Azure Synapse environment but not too large to quickly demonstrate value. A size in the 1-10 terabyte range is typical.

For your initial migration project, minimize the risk, effort, and migration time so you can quickly see the benefits of the Azure cloud environment. Both the lift-and-shift and phased migration approaches limit the scope of the initial migration to just the data marts and don't address broader migration aspects such as ETL migration and historical data migration. However, you can address those aspects in later phases of the project once the migrated data mart layer is backfilled with data and the required build processes.

Lift and shift migration vs. Phased approach

In general, there are two types of migration regardless of the purpose and scope of the planned migration: lift and shift as-is and a phased approach that incorporates changes.

Lift and shift

In a lift and shift migration, an existing data model, like a star schema, is migrated unchanged to the new Azure Synapse platform. This approach minimizes risk and migration time by reducing the work needed to realize the benefits of moving to the Azure cloud environment. Lift and shift migration is a good fit for these scenarios:

  • You have an existing Netezza environment with a single data mart to migrate, or
  • You have an existing Netezza environment with data that's already in a well-designed star or snowflake schema, or
  • You're under time and cost pressures to move to a modern cloud environment.

Tip

Lift and shift is a good starting point, even if subsequent phases implement changes to the data model.

Phased approach that incorporates changes

If a legacy data warehouse has evolved over a long period of time, you might need to re-engineer it to maintain the required performance levels. You might also have to re-engineer to support new data like Internet of Things (IoT) streams. As part of the re-engineering process, migrate to Azure Synapse to get the benefits of a scalable cloud environment. Migration can also include a change in the underlying data model, such as a move from an Inmon model to a data vault.

Microsoft recommends moving your existing data model as-is to Azure and using the performance and flexibility of the Azure environment to apply the re-engineering changes. That way, you can use Azure's capabilities to make the changes without impacting the existing source system.

Use Azure Data Factory to implement a metadata-driven migration

You can automate and orchestrate the migration process by using the capabilities of the Azure environment. This approach minimizes the performance hit on the existing Netezza environment, which may already be running close to capacity.

Azure Data Factory is a cloud-based data integration service that supports creating data-driven workflows in the cloud that orchestrate and automate data movement and data transformation. You can use Data Factory to create and schedule data-driven workflows (pipelines) that ingest data from disparate data stores. Data Factory can process and transform data by using compute services such as Azure HDInsight Hadoop, Spark, Azure Data Lake Analytics, and Azure Machine Learning.

When you're planning to use Data Factory facilities to manage the migration process, create metadata that lists all the data tables to be migrated and their location.

Design differences between Netezza and Azure Synapse

As mentioned earlier, there are some basic differences in approach between Netezza and Azure Synapse Analytics databases and these differences are discussed next.

Multiple databases vs. a single database and schemas

The Netezza environment often contains multiple separate databases. For instance, there could be separate databases for: data ingestion and staging tables, core warehouse tables, and data marts (sometimes referred to as the semantic layer). ETL or ELT pipeline processes might implement cross-database joins and move data between the separate databases.

In contrast, the Azure Synapse environment contains a single database and uses schemas to separate tables into logically separate groups. We recommend that you use a series of schemas within the target Azure Synapse database to mimic the separate databases migrated from the Netezza environment. If the Netezza environment already uses schemas, you may need to use a new naming convention when you move the existing Netezza tables and views to the new environment. For example, you could concatenate the existing Netezza schema and table names into the new Azure Synapse table name, and use schema names in the new environment to maintain the original separate database names. If schema consolidation naming has dots, Azure Synapse Spark might have issues. Although you can use SQL views on top of the underlying tables to maintain the logical structures, there are potential downsides to that approach:

  • Views in Azure Synapse are read-only, so any updates to the data must take place on the underlying base tables.

  • There may already be one or more layers of views in existence and adding an extra layer of views could affect performance and supportability because nested views are difficult to troubleshoot.

Tip

Combine multiple databases into a single database within Azure Synapse and use schema names to logically separate the tables.

Table considerations

When you migrate tables between different environments, typically only the raw data and the metadata that describes it physically migrate. Other database elements from the source system, such as indexes, usually aren't migrated because they might be unnecessary or implemented differently in the new environment.

Performance optimizations in the source environment, such as indexes, indicate where you might add performance optimization in the new environment. For example, if queries in the source Netezza environment frequently use zone maps, that suggests that a non-clustered index should be created within Azure Synapse. Other native performance optimization techniques like table replication may be more applicable than straight like-for-like index creation.

Tip

Existing indexes indicate candidates for indexing in the migrated warehouse.

Unsupported Netezza database object types

Netezza-specific features can often be replaced by Azure Synapse features. However, some Netezza database objects aren't directly supported in Azure Synapse. The following list of unsupported Netezza database objects describes how you can achieve an equivalent functionality in Azure Synapse.

  • Zone maps: in Netezza, zone maps are automatically created and maintained for the following column types and are used at query time to restrict the amount of data to be scanned:

    • INTEGER columns of length 8 bytes or less.
    • Temporal columns, such as DATE, TIME, and TIMESTAMP.
    • CHAR columns if they're part of a materialized view and mentioned in the ORDER BY clause.

    You can find out which columns have zone maps by using the nz_zonemap utility, which is part of the NZ Toolkit. Azure Synapse doesn't include zone maps, but you can achieve similar results by using other user-defined index types and/or partitioning.

  • Clustered base tables (CBT): in Netezza, CBTs are commonly used for fact tables, which can have billions of records. Scanning such a huge table requires considerable processing time because a full table scan might be needed to get the relevant records. Organizing records on restrictive CBTs allows Netezza to group records in same or nearby extents. This process also creates zone maps that improve the performance by reducing the amount of data that needs to be scanned.

    In Azure Synapse, you can achieve a similar effect by partitioning and/or using other indexes.

  • Materialized views: Netezza supports materialized views and recommends using one or more materialized views for large tables with many columns if only a few columns are regularly used in queries. Materialized views are automatically refreshed by the system when data in the base table is updated.

    Azure Synapse supports materialized views, with the same functionality as Netezza.

Netezza data type mapping

Most Netezza data types have a direct equivalent in Azure Synapse. The following table shows the recommended approach for mapping Netezza data types to Azure Synapse.

Netezza Data Type Azure Synapse Data Type
BIGINT BIGINT
BINARY VARYING(n) VARBINARY(n)
BOOLEAN BIT
BYTEINT TINYINT
CHARACTER VARYING(n) VARCHAR(n)
CHARACTER(n) CHAR(n)
DATE DATE(date)
DECIMAL(p,s) DECIMAL(p,s)
DOUBLE PRECISION FLOAT
FLOAT(n) FLOAT(n)
INTEGER INT
INTERVAL INTERVAL data types aren't currently directly supported in Azure Synapse, but can be calculated using temporal functions such as DATEDIFF.
MONEY MONEY
NATIONAL CHARACTER VARYING(n) NVARCHAR(n)
NATIONAL CHARACTER(n) NCHAR(n)
NUMERIC(p,s) NUMERIC(p,s)
REAL REAL
SMALLINT SMALLINT
ST_GEOMETRY(n) Spatial data types such as ST_GEOMETRY aren't currently supported in Azure Synapse, but the data could be stored as VARCHAR or VARBINARY.
TIME TIME
TIME WITH TIME ZONE DATETIMEOFFSET
TIMESTAMP DATETIME

Tip

Assess the number and type of unsupported data types during the migration preparation phase.

Third-party vendors offer tools and services to automate migration, including the mapping of data types. If a third-party ETL tool is already in use in the Netezza environment, use that tool to implement any required data transformations.

SQL DML syntax differences

SQL DML syntax differences exist between Netezza SQL and Azure Synapse T-SQL. Those differences are discussed in detail in Minimize SQL issues for Netezza migrations.

  • STRPOS: in Netezza, the STRPOS function returns the position of a substring within a string. The equivalent function in Azure Synapse is CHARINDEX with the order of the arguments reversed. For example, SELECT STRPOS('abcdef','def')... in Netezza is equivalent to SELECT CHARINDEX('def','abcdef')... in Azure Synapse.

  • AGE: Netezza supports the AGE operator to give the interval between two temporal values, such as timestamps or dates, for example: SELECT AGE('23-03-1956','01-01-2019') FROM.... In Azure Synapse, use DATEDIFF to get the interval, for example: SELECT DATEDIFF(day, '1956-03-26','2019-01-01') FROM.... Note the date representation sequence.

  • NOW(): Netezza uses NOW() to represent CURRENT_TIMESTAMP in Azure Synapse.

Functions, stored procedures, and sequences

When migrating a data warehouse from a mature environment like Netezza, you probably need to migrate elements other than simple tables and views. Check whether tools within the Azure environment can replace the functionality of functions, stored procedures, and sequences because it's usually more efficient to use built-in Azure tools than to recode those elements for Azure Synapse.

As part of your preparation phase, create an inventory of objects that need to be migrated, define a method for handling them, and allocate appropriate resources in your migration plan.

Data integration partners offer tools and services that can automate the migration of functions, stored procedures, and sequences.

The following sections further discuss the migration of functions, stored procedures, and sequences.

Functions

As with most database products, Netezza supports system and user-defined functions within a SQL implementation. When you migrate a legacy database platform to Azure Synapse, common system functions can usually be migrated without change. Some system functions might have a slightly different syntax, but any required changes can be automated.

For Netezza system functions or arbitrary user-defined functions that have no equivalent in Azure Synapse, recode those functions using a target environment language. Netezza user-defined functions are coded in nzlua or C++ languages. Azure Synapse uses the Transact-SQL language to implement user-defined functions.

Stored procedures

Most modern database products support storing procedures within the database. Netezza provides the NZPLSQL language, which is based on Postgres PL/pgSQL, for this purpose. A stored procedure typically contains both SQL statements and procedural logic, and returns data or a status.

Azure Synapse supports stored procedures using T-SQL, so you need to recode any migrated stored procedures in that language.

Sequences

In Netezza, a sequence is a named database object created using CREATE SEQUENCE. A sequence provides unique numeric values via the NEXT VALUE FOR method. You can use the generated unique numbers as surrogate key values for primary keys.

Azure Synapse doesn't implement CREATE SEQUENCE, but you can implement sequences using IDENTITY columns or SQL code that generates the next sequence number in a series.

Extract metadata and data from a Netezza environment

Data Definition Language (DDL) generation

The ANSI SQL standard defines the basic syntax for Data Definition Language (DDL) commands. Some DDL commands, such as CREATE TABLE and CREATE VIEW, are common to both Netezza and Azure Synapse but have been extended to provide implementation-specific features.

You can edit existing Netezza CREATE TABLE and CREATE VIEW scripts to achieve equivalent definitions in Azure Synapse. To do so, you might need to use modified data types and remove or modify Netezza-specific clauses such as ORGANIZE ON.

Within the Netezza environment, system catalog tables specify the current table and view definition. Unlike user-maintained documentation, system catalog information is always complete and in sync with current table definitions. By using utilities such as nz_ddl_table, you can access system catalog information to generate CREATE TABLE DDL statements that create equivalent tables in Azure Synapse.

You can also use third-party migration and ETL tools that process system catalog information to achieve similar results.

Data extraction from Netezza

You can extract raw table data from Netezza tables to flat delimited files, such as CSV files, using standard Netezza utilities like nzsql and nzunload, or via external tables. Then, you can compress the flat delimited files using gzip, and upload the compressed files to Azure Blob Storage using AzCopy or Azure data transport tools like Azure Data Box.

Extract table data as efficiently as possible. Use the external tables approach because it's the fastest extract method. Perform multiple extracts in parallel to maximize data extraction throughput. The following SQL statement performs an external table extract:

CREATE EXTERNAL TABLE '/tmp/export_tab1.csv' USING (DELIM ',') AS SELECT * from <TABLENAME>;

If sufficient network bandwidth is available, you can extract data from an on-premises Netezza system directly into Azure Synapse tables or Azure Blob Data Storage. To do so, use Data Factory processes or third-party data migration or ETL products.

Tip

Use Netezza external tables for the most efficient data extraction.

Extracted data files should contain delimited text in CSV, Optimized Row Columnar (ORC), or Parquet format.

For more information about migrating data and ETL from a Netezza environment, see Data migration, ETL, and load for Netezza migrations.

Performance recommendations for Netezza migrations

The goal of performance optimization is same or better data warehouse performance after migration to Azure Synapse.

Similarities in performance tuning approach concepts

Many performance tuning concepts for Netezza databases hold true for Azure Synapse databases. For example:

  • Use data distribution to collocate data-to-be-joined onto the same processing node.

  • Use the smallest data type for a given column to save storage space and accelerate query processing.

  • Ensure that columns to be joined have the same data type in order to optimize join processing and reduce the need for data transforms.

  • To help the optimizer produce the best execution plan, ensure statistics are up to date.

  • Monitor performance using built-in database capabilities to ensure that resources are being used efficiently.

Tip

Prioritize familiarity with the tuning options in Azure Synapse at the start of a migration.

Differences in performance tuning approach

This section highlights low-level performance tuning implementation differences between Netezza and Azure Synapse.

Data distribution options

For performance, Azure Synapse was designed with multi-node architecture and uses parallel processing. To optimize table performance, you can define a data distribution option in CREATE TABLE statements using DISTRIBUTION in Azure Synapse and DISTRIBUTE ON in Netezza.

Unlike Netezza, Azure Synapse supports local joins between a small table and a large table through small table replication. For instance, consider a small dimension table and a large fact table within a star schema model. Azure Synapse can replicate the smaller dimension table across all nodes to ensure that the value of any join key for the large table has a matching, locally available dimension row. The overhead of dimension table replication is relatively low for a small dimension table. For large dimension tables, a hash distribution approach is more appropriate. For more information about data distribution options, see Design guidance for using replicated tables and Guidance for designing distributed tables.

Data indexing

Azure Synapse supports several user-definable indexing options that have a different operation and usage compared to system-managed zone maps in Netezza. For more information about the different indexing options in Azure Synapse, see Indexes on dedicated SQL pool tables.

The existing system-managed zone maps within a source Netezza environment provide a useful indication of data usage and the candidate columns for indexing in the Azure Synapse environment.

Data partitioning

In an enterprise data warehouse, fact tables can contain billions of rows. Partitioning optimizes the maintenance and query performance of these tables by splitting them into separate parts to reduce the amount of data processed. In Azure Synapse, the CREATE TABLE statement defines the partitioning specification for a table.

You can only use one field per table for partitioning. That field is often a date field because many queries are filtered by date or date range. It's possible to change the partitioning of a table after initial load by using the CREATE TABLE AS (CTAS) statement to recreate the table with a new distribution. For a detailed discussion of partitioning in Azure Synapse, see Partitioning tables in dedicated SQL pool.

Data table statistics

You should ensure that statistics on data tables are up to date by building in a statistics step to ETL/ELT jobs.

PolyBase or COPY INTO for data loading

PolyBase supports efficient loading of large amounts of data to a data warehouse by using parallel loading streams. For more information, see PolyBase data loading strategy.

COPY INTO also supports high-throughput data ingestion, and:

  • Data retrieval from all files within a folder and subfolders.

  • Data retrieval from multiple locations in the same storage account. You can specify multiple locations by using comma separated paths.

  • Azure Data Lake Storage (ADLS) and Azure Blob Storage.

  • CSV, PARQUET, and ORC file formats.

Workload management

Running mixed workloads can pose resource challenges on busy systems. A successful workload management scheme effectively manages resources, ensures highly efficient resource utilization, and maximizes return on investment (ROI). Workload classification, workload importance, and workload isolation give more control over how workload utilizes system resources.

The workload management guide describes the techniques to analyze the workload, manage and monitor workload importance, and the steps to convert a resource class to a workload group. Use the Azure portal and T-SQL queries on DMVs to monitor the workload to ensure that the applicable resources are efficiently utilized.

Next steps

To learn about ETL and load for Netezza migration, see the next article in this series: Data migration, ETL, and load for Netezza migrations.