PGConf.Online 2021

In this talk we want to present how Microsoft team composed of people from two different teams approached the project and solved the migration issues using ora2pg and was able to prove that Postgres Single Server can perform equally well as Oracle Exadata. We will present our ways of working and also some main technical challenges that we faced including migration of BULK COLLECT’s, hierarchical queries, refcursors and others more complicated Oracle constructs.

The story about a challenging PoC that proved that Postgres can achieve the same performance as Oracle Exadata. The schema that was migrated wasn’t the simplest one you might see. It was quite the opposite. The code was loaded with dynamic queries, BULK COLLECT’s, nested loops, CONNECT BY statements, global variables and lot of dependencies. Ora2pg did a great job converting the schema but left a lot of work to do manually. Also estimates produced by the tool were highly inaccurate since the logic required not the migration but total re-architecture of the code. In this talk we want to present how Microsoft team composed of people from two different teams approached the project and solved the migration issues using ora2pg and was able to prove that Postgres Single Server can perform equally well as Oracle Exadata. We will present our ways of working and also some main technical challenges that we faced including:

• How estimates do (not) work
• How we handled BULK COLLECT’s
• Why we got rid of refcursors
• How we got stuck with testing of one the packages and how the help from a friend solved the problem
• How we handled hierarchical queries and drilling down the hierarchy

Fast text search queries can be made even faster with indexing on lexemes inside compound records of tsvector format. RUM index is an open-source PostgreSQL extension. It represents a big improvement of GIN index and it can index lexemes with additional information e.g. tsvector lexeme weight-mark. So it can support tsvector capabilities more.

Until recently it was needed to recheck results of weight-containing queries by table. My modification (2020) is to make the processing of this kind of queries index-only and therefore much faster.

Also, I will describe and provide benchmarks for different usage cases for fast text search. We'll see how RUM index can improve the performance and compare it with PostgreSQL internal GIN index.

Some OS distributions do not have a pcs configuration utility to create a high availability cluster PostgreSQL. In this case, the crm utility from the crmsh package will help us. It is more difficult to use, but powerful and effective.

In my master class, I will show how to use this utility, as well as configure a failover cluster in different configurations.

Okko is one of the largest legal online cinemas in Russia. Our catalog contains 60 000 movies, cartoons and TV series. Since its starting, the service has been visited by over 20 million users. The monthly audience is 2.8 million people. All these figures speak of a reliable high-load service.

As DBA, I will mainly talk about databases (PostgreSQL, Cassandra, Redis) that are used in the company. We'll take a closer look at PostgreSQL on the topics of high loads, monitoring, optimization, backup and recovery.