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Category: Performance Tuning

Bucketing Data in Hive

Chitra Sapkal explains why bucketing in Hive can be so powerful:

When a column has a high cardinality, we can’t perform partitioning on it. A very high number of partitions will generate too many Hadoop files which would increase the load on the node. That’s because the node will have to keep the metadata of every partition, and that would affect the performance of that node

In simple words, You can use bucketing if you need to run queries on columns that have huge data, which makes it difficult to create partitions.

Click through to see how bucketing works and examples of how you can use it to make queries faster.

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Improving Managed Instance Load Performance

Niko Neugebauer provides some tips on improving data load performance when using SQL Managed Instances in the General Purpose tier:

In this blog post we shall consider some of the strategies for improving data loading performance in Azure SQL Managed Instance. These strategies apply to the repeatable ETL processes, meaning that if there a problem, data loading process can be repeated without loss of any bit of data or its consistency. Of course, these strategies do require a prepared design for the possibility of the repetition, but this is a basic requirement for any data loading process.

There are many great ways of ensuring high performance data loading and this blog post does not pretend to be exhaustive an ultimate resource, but it will provide a couple of known paths that can drastically improve the performance of the Log Throughput in Azure SQL MI.

Click through for some tips, including some which make sense on-prem and a couple which are specific to platform-as-a-service offerings.

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The Performance Impact of Dissimilarly-Sized tempdb Files

Chris Taylor puts on the lab coat and safety goggles:

tldr: Over the years I’ve read a lot of blog posts and watched a lot of videos where they mention that you should have your tempdb files all the same size. What I haven’t seen much of (if any) is what performance impact you actually see if they are not configured optimally. This blog post aims to address that

It is not too long, so do read.

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Lessons Learned Troubleshooting High CPU in Azure SQL DB

Kendra Little has an after-action report:

I’ve just had the pleasure of publishing my first new article in the Microsoft Docs, Diagnose and troubleshoot high CPU on Azure SQL Database.

This article isn’t really “mine” – anyone in the community can create a Pull Request to suggest changes, or others at Microsoft may take it in a different direction. But I got to handle the outlining, drafting, and incorporation of suggested changes for the initial publication.

It was a ton of fun, and I learned a lot about Azure SQL Database in the process.

Click through for what Kendra learned specific to Azure SQL Database, and also read the article itself.

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Dedicated SQL Pool Index, Distribution, and Partition Guidance

I have a write-up on the specific value of distributions, indexes, and partitions in Azure Synapse Analytics dedicated SQL pools:

Not too long ago, I ended up taking the DP-203 certification exam for sundry reasons. On that exam, they ask a lot about Azure Synapse Analytics, including indexing, distribution, and partitioning strategies. Because these can be a bit different from on-premises SQL Server, I wanted to cover what options are available and when you might choose them. Let’s start with distributions, as that’s the biggest change in thought process.

Read on for the guidance.

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Spark SQL Bucketing and Query Tuning

Tomaz Kastrun continues a series on Apache Spark. Part 13 looks at bucketing and partitioning in Spark SQL:

Partitioning and Bucketing in Hive are used to improve performance by eliminating table scans when dealing with a large set of data on a Hadoop file system (HDFS). The major difference between them is how they split the data.

Part 14 covers query hints:

This hint instructs Spark to use the hinted strategy on specified relation when joining tables together. When BROADCASTJOIN hint is used on Data1 table with Data2 table and overrides the suggested setting of statistics from configuration spark.sql.autoBroadcastJoinThreshold.

Spark also prioritise the join strategy, and also when different JOIN strategies are used, Spark SQL will always prioritise them.

Be sure to check those out.

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Batch Mode and Window Functions

I wind down a series on window functions:

SQL Server typically operates in row mode, which means that an operator processes one row at a time. This sounds inefficient, but tends to work out pretty well in practice. However, something which may work out even better is to process more than one row at a time, especially when the number of rows gets to be fairly large. Enter batch mode.

Batch mode was introduced in SQL Server 2012 alongside non-clustered columnstore indexes. It became interesting in SQL Server 2016 and very interesting in SQL Server 2019. That’s because 2016 introduced writable clustered columnstore indexes and 2019 gives us batch mode outside of columnstore indexes.

There are some nice potential performance gains for queries involving window functions.

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Storage Testing for Azure SQL Managed Instances

Joe Obbish busts out the slide rule:

Lately I’ve been doing some exploratory performance testing on Azure SQL Managed Instances in preparation for a migration to that platform. This blog post documents some storage testing results and may even have practical advice near the end. All testing was done on a gen5 general purpose instance with 8 vCores.

Read on for Joe’s findings. Spoiler alert: there is practical advice at the end.

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