Two counters instead of a materialized view
Blog post from Mergify
Rémy Duthu's blog post delves into the intricacies of building a custom metric rollup system on Postgres, emphasizing the limitations of using materialized views for handling high-frequency data updates. The author explains that while materialized views are useful for static data or infrequent updates, they fall short in scenarios where data is frequently written and then deleted, such as in their CI job metrics system. Instead of relying on materialized views, the team developed a two-writer, two-counter mechanism that effectively manages data retention and update efficiency by incrementally updating metrics with a combination of synchronous and asynchronous processes. This system utilizes a synchronous writer for immediate updates and an asynchronous writer for periodic recalculations, effectively balancing data freshness with computational efficiency. Duthu highlights the importance of using two counters instead of a boolean flag to avoid race conditions during asynchronous recalculations, ensuring that metrics remain accurate despite concurrent data writes. The blog concludes by recommending the use of materialized views only in scenarios where data changes infrequently, while advocating for their custom approach in high-write environments to maintain performance and accuracy.
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