On Wed, 2023-07-26 at 18:15 +0530, Piyush Katariya wrote: > I have a few queries regarding the TOAST Fields serialisation/deserialization > performance. > > The use case i am trying to solve here is to have millions of partitions and > aggregate the data in array field. > > I wish to know if i declare certain column in table as "array of UDT/JSONB" > and enable > either lz4 or zstd compression on it, does appending or prepending to that > array or even > changing the intermediate fields of UDT/JSONB objects. in that array has a > runtime cost > of full array data de-serialization every single time. If i perform any > UPDATE operation > on its elements or add/remove new elements from any position, does PG > rewrites the new > version of the column value regardless of its size.
Updating even a small part of a large JSONB value requires that the entire thing is read and written, causing a lot of data churn. This is inefficient, and you shouldn't use large JSONB values if you plan to do that. If the data have a regular structure, use a regular relational data model. Otherwise, one idea might be to split the JSONB in several parts and store each of those parts in a different table row. That would reduce the impact. Yours, Laurenz Albe
