v.21.3Performance Improvement
Add compress setting for Memory tables to reduce RAM usage
Addcompresssetting forMemorytables. If it's enabled the table will use less RAM. On some machines and datasets it can also work faster on SELECT, but it is not always the case. This closes #20093. Note: there are reasons why Memory tables can work slower than MergeTree: (1) lack of compression (2) static size of blocks (3) lack of indices and prewhere... #20168 (alexey-milovidov).