Shrink TOAST bloat from wide rows
Large values live in a separate TOAST table and it bloats independently. A real PG16 lab grew from about 8 MB to 40 MB under four updates; VACUUM FULL brought it back to about 10 MB.
Problem
What you're actually looking at
The symptom as it shows up on a real server.
When a column value is too big for a page, PostgreSQL stores it out-of-line in a TOAST table. That TOAST table has its own dead tuples and its own bloat, which a glance at the main heap size completely misses. You have to size the TOAST relation explicitly.
Meridian stores large document bodies in document_blobs. The main heap is only ~1.3 MB, but updates to the big values have bloated the hidden TOAST table to hundreds of MB.
Simple terms
When a column value is too big to fit on a normal page, PostgreSQL stashes it in a hidden side table called TOAST. That side table collects its own dead rows and bloats on its own, and if you only look at the main table's size, you will miss it completely. The main heap can be tiny while the hidden TOAST table has grown to hundreds of megabytes. You have to check the TOAST size directly to see it.
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