Investigate steady increase in redis persistent memory usage

Initially raised in #2471 (comment 1568594676), we are seeing a steady increase of redis-persistent memory usage roughly at a rate of ~100 MB/week, starting from the week of 2023-08-20. Note the increase in the weekend's baseline below.

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This issue aims to investigate and mitigate the root cause of the growth. We are not in any saturation event in the near future, especially once we've moved this instance to Redis Cluster with bigger capacity, but it'd be preferable to address this early.