PrestoDB Questions & Answers

First, Overall Differences Both AWS Athena and Ahana Cloud are based on the popular open-source Presto project which was originally developed by Facebook and later donated to the Linux Foundation’s … Continue reading How does the Price-Performance ratio of AWS Athena Presto compare to Ahana Cloud for Presto?

Typically you’ll use AWS Glue to create the data sources and tables that Athena will query. You could also create your tables using Athena and then use the tables in … Continue reading What are the AWS Glue partition limits and does it apply to AWS Athena?

What level of concurrency performance can I expect using Presto as part of the AWS Athena service? I’m getting a lot of my workloads queued up when I use AWS … Continue reading Concurrency Performance Using Presto With AWS Athena Service | Ahana

How do I get deterministic performance out of Amazon Athena? What is Athena? Amazon Athena is an interactive query service based on Presto that makes it easy to analyze data … Continue reading Getting Deterministic Performance Out Of Amazon Athena Guide | Ahana

Do I have to use AWS Lambda to connect to data sources with Athena? The Athena Federated Query Journey AWS announced the public preview of Athena federated query in November … Continue reading Using AWS Lambda To Connect To Data Sources With Athena | Ahana

How do I do geospatial queries and spatial joins in Presto? A question that often comes up is “how do I do geospatial queries and spatial joins in Presto?”. Fortunately … Continue reading Geospatial Queries & Spatial Joins In Presto Guide | Ahana

How do I query JSON documents with Presto? JSON documents are a common data type. A lot of people collect logs and load them into s3. Then in order to … Continue reading How Do I Query JSON Documents With Presto | Query JSON Docs | Ahana

Is there latency overhead for Presto queries if everything fits into memory and doesn’t need to be distributed? Presto is both in-memory and distributed, so each work has memory and … Continue reading Latency Overhead For Presto Queries If Fits Into Memory | Ahana

Is the Hive metastore a hard dependency of Presto, or could Presto be configured to use something else like Postgres? With Presto, there’s no hard dependency of having to use … Continue reading Is Hive Metastore Hard Dependency Of Presto | Postgres With Presto | Ahana

What are the differences between Presto and Apache Drill? Drill is an open source SQL query engine which began life as a paper “Dremel: Interactive Analysis of Web-Scale Datasets” from … Continue reading Differences Between Presto & Apache Drill | Ahana

Why am I getting zero records when I use AWS Athena to query a CSV file? There’s a common error many AWS Athena users see when they query CSV files … Continue reading Zero Records Returned CSV | Zero Records AWS Athena | Ahana

Does Presto work natively with GraphQL? Some users may have a primary data store that is GraphQL-based (AWS AppSync) and want to leverage Presto. For context, GraphQL falls in the … Continue reading Presto Graphql | Does Presto Work Natively With GraphQL | Ahana

Why does a single AWS Athena query get stuck in QUEUED state before being executed? One of the drawbacks of AWS Athena is the fact that as a user, you … Continue reading Athena Query Waiting In Queue | Athena Query Stuck | Ahana

Because Presto is a distributed system composed of a coordinator and workers, each worker can connect to one or more data sources through corresponding connectors. The coordinator receives the query … Continue reading How Does Presto Join Data?

Executing Presto queries on Spark is possible, but why leverage Spark as an execution framework for Presto’s queries when Presto is itself an efficient execution engine?  The fact that both … Continue reading Executing Presto Spark

When I run a query with AWS Athena, I get the error message ‘query exhausted resources on this scale factor’. Why? AWS Athena is well documented in having performance issues, … Continue reading Query Exhausted Resources On This Scale Factor Error | Ahana

Creating tables in a S3 Bucket gives “Query failed External location must be a directory” Using Presto’s Hive connector you want to create a new table in a directory that … Continue reading Creating Tables In A S3 Bucket Issues | Ahana

Big Data Query When it comes to querying big data using standard SQL you have come to the right place as this is what Presto was designed to do. Presto, … Continue reading Big Data Query | Presto Big Data | Ahana

I use RDS Postgres databases and need some complex queries done which tend to slow down my databases for everyone else on the system. What do I need to consider … Continue reading RDS Postgres Databases Complex Queries | Ahana

Advanced SQL Tutorial JSON Presto has a wide-range of JSON functions. Consider this json test input data (represented in the query using the  VALUES function) which contains 3 key/value elements. … Continue reading Advanced SQL Tutorial & Advanced SQL Queries | Ahana

Complex SQL Queries Complex SQL queries benefit from Presto’s distributed, parallel, in-memory processing architecture and cost-based optimizer. And with Presto’s federation capabilities even more complex queries can be unleashed on … Continue reading Complex SQL Queries | SQL Complex Queries | Ahana

Advanced SQL Queries with Presto Advanced SQL features and functions are used by analysts when, for example, complex calculations are needed, or when many tables (perhaps from multiple sources) need … Continue reading Advanced SQL Queries with Presto | SQL Queries Presto | Ahana

Presto Platform Overview Presto is an open source distributed SQL query engine for running interactive analytic queries against data sources of all sizes. Some of the world’s most innovative and … Continue reading Presto Platform Overview & Scaling | Interactive Analytic Queries

How To Stop Presto If you are using the presto-admin tool this is how to stop Presto safely: $ presto-admin server stop In addition these commands are also useful: presto-admin … Continue reading How To Stop Presto | Presto Admin & EMR Restart | Ahana

Presto New Releases Where is the latest release of PrestoDB? And where can I find the release notes? Where is the documentation? These are common questions with easy answers. Presto’s … Continue reading Presto New Releases | Presto New & Latest Release | Ahana

How Much Memory Should I Give A Presto Worker Node? Presto is an in-memory query engine and so naturally memory configuration and management is important.   JVM Memory Presto’s JVM memory … Continue reading How Much Memory Should I Give A Presto Worker Node | Presto Memory

How do I show tables from all schemas with Presto? In Presto it is straightforward to show all tables in a schema e.g. If we have a MySQL data source/catalog … Continue reading Show Tables From Schemas With Presto | Ahana

How do I convert Bigint to Timestamp with Presto? UNIX timestamps are normally stored as doubles. If you have UNIX timestamps stored as big integers then you may encounter errors … Continue reading Convert Bigint To Timestamp With Presto | Ahana

How do I convert timestamp to date with Presto? Luckily Presto has a wide range of conversion functions and they are listed in the docs.  Many of these allow us … Continue reading Convert Timestamp To Date With Presto | Ahana

How do I configure Case Sensitive Search with Presto? When dealing with character data, case sensitivity can be important when  searching for specific matches or patterns. But not all databases … Continue reading Configure Case Sensitive Search With Presto | Ahana

When should I use ORC versus Parquet when using Presto? If you’re working with open data lakes using open source and open formats, you can have multiple formats. Presto works … Continue reading Use ORC Versus Parquet When Using Presto | Ahana

What’s the advantage of having your own Hive metastore with Presto? How does it compare to Amazon Glue? First let’s define what Apache Hive is versus Amazon Glue. Apache Hive … Continue reading Benefits Of Hive Metastore With Presto | Ahana

Presto has a typeof() function to make finding the data type of a value easy. This is particularly useful when you are getting values from nested maps for example and … Continue reading How do you find out data type of value with Presto?

How do you rotate rows to columns with Presto? Sometimes called pivoting, here is one example of how to rotate row data with Presto.   Suppose we have rows of data … Continue reading Rotate Rows To Columns With Presto | Ahana

Sometimes called unpivoting, here is one example of how to rotate column data with Presto.   Suppose we have some integer data arranged in two columns called a and b: a … Continue reading How do you rotate columns to rows with Presto?

What are the operational benefits of using a managed service for Presto with Ahana Cloud? First let’s hear from an AWS Solution Architect: “Ahana Cloud uses the best practices of … Continue reading Benefits Of Using Managed Service For Presto | Ahana

Hive’s explode() function takes an array (or a map) as input and outputs the elements of the array (map) as separate rows. Explode is a built-in Table-Generating Function (UDTF) in … Continue reading How do you do a Lateral View Explode in Presto?

Here’s an example using test results data in json form as input, from which we compute the average score per student.  We use the WITH clause to define a common … Continue reading How do you cross join unnest a JSON array?

With Ahana Cloud, we’ve made it easy for you write output of queries to S3. While there’s a variety of formats, here’s an example:

With Amazon Athena you’re limited in scope when it comes to doing joins across other data sources like relational data systems and more. You have to set up a Lambda, … Continue reading Does Amazon Athena do joins across other data sources besides S3? Does Amazon Athena connect to other data sources?

If you’re managing Presto on your own, either through your own installation or through a service like AWS EMR or AWS Athena, you have to maintain and manage all of … Continue reading If I have catalogs connected and configurations attached to my Presto cluster, what happens when I take the cluster down?

Check if Presto map or array is empty When working with array (indexable lists) or map (key-value tuple) complex types in Presto, it is useful to be able to test … Continue reading Check If Map Or Presto Array Is Empty Or Contains | Ahana

Export result of Select statement A common question is “how can I run a query and export the result set quickly and easily in Presto?”  You are in luck, as … Continue reading Export Result Of Select Statement | Ahana

Presto queries running slow? Reasons for Presto queries running slow, diagnosis, tuning, things to check and possible solutions: How many workers do you have in your cluster? If your PrestoDB … Continue reading Presto Queries Running Slow | Presto Slow | Ahana

Extract keys in a nested JSON array object Let’s say we have some JSON that looks like this: In this instance our json contains key value pairs. How can we … Continue reading Extract Keys In A Nested JSON Array Object | Ahana

Generate Interval from Variable Using PrestoDB There are numerous ways of generating intervals using PrestoDB SQL for different data types. Dates Date intervals can be generated for a given date … Continue reading Generate Interval from Variable Using PrestoDB | Ahana

How To Escape a Single Quote With Presto In reality there will be some occasions when you need to use a quote character in your data, in your query, or … Continue reading How To Presto Escape Single Quote | Pesto Escape Quote | Ahana

Check if null and return default (NVL analog) SQL has a number of functions for dealing with null values, and everyone has their favorite. The complicating factor is that not … Continue reading Check If Null & Return Default (NVL analog) | Ahana

Static date and timestamp in where clause Many databases automatically convert between CHAR or VARCHAR and other types like DATE and TIMESTAMP as a convenience feature.  Using constants in a … Continue reading Static Date & Timestamp In Where Clause | PrestoDB Timestamp

Where can I find the Presto Server Bootstrap logs? A common question is “where are Presto’s bootstrap logs?”  These are logs that indicate what is happening to the cluster on … Continue reading Where Can I Find The Presto Server Bootstrap Logs | Ahana