I have been experiencing some sudden momentary dips in the available aws rds free storage space available. Once the free space dips it goes into the storage optimization mode.

I have a postgres table which is around 100gb with around 280 mill records to which constant updates happen. The table has a toast of around 300gb. I'm not able to think where to even point the issue at while looking at cloud watch. These dips are making the product a lot slower. I have looked at enhanced monitoring and seen all the different charts and can't see any unusual spikes either with os or db processes in cloudwatch during the time these dips happened.

Below is an attached picture. Please let me know if you guys have any ideas why this might be happening?

enter image description here

  • Could be anything. Figure out what exactly the graph measures. Figure out what you were doing at the time. Something like DROP TABLE, TRUNCATE or VACUUM (FULL)? But perhaps this drop is related to WAL getting deleted, which could have been delayed by archiving or a stale replication slot. You see, this is unanswerable without more information. Ah, the joys of hosted databases! Commented Apr 5, 2023 at 1:35
  • Could it be the storage used by temp files for large sorts or hash joins? I don't know how those show up in "cloud watch"
    – jjanes
    Commented Apr 5, 2023 at 11:53


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