https://sauvikbiswas.com/tags/postgres/ Recent content in Postgres on Sauvik Biswas Hugo en-us Thu, 14 May 2026 00:00:00 +0000 https://sauvikbiswas.com/posts/debezium-and-growing-pg-wal/ Thu, 14 May 2026 00:00:00 +0000 https://sauvikbiswas.com/posts/debezium-and-growing-pg-wal/ <h1 class="heading" id="a-problem-in-production"> A problem in production <a class="anchor" href="#a-problem-in-production">#</a> </h1> <p>A couple of days ago, our stack saw a massive rise in WAL. As a side effect, we weren&rsquo;t seeing Debezium emit CDC messages to Kafka, which in turn affected some critical workflows from advancing. This was not the first time this had happened. One idea that was thrown around was to limit the tables Debezium subscribes to. However, that doesn&rsquo;t help.</p> <p>Limiting which tables Debezium subscribes to (via the Postgres <code>PUBLICATION</code>) reduces the <strong>events Debezium emits</strong>, but it does <strong>not</strong> reduce what Postgres has to <strong>keep on disk</strong>. WAL retention is governed by the <em>replication slot</em>, not by the publication. If the slot doesn&rsquo;t advance, <code>pg_wal</code> keeps growing, even if Debezium is &ldquo;quiet.&rdquo;</p>