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Reading here I cannot find a clear answer: http://www.postgresql.org/docs/9.1/static/storage-toast.html

I need to know if setting storage to EXTERNAL for a particular column, I can gain a little performance. Most of my data is retrieved from SHARED_BUFFERS.

I'm curious to know if decompression is done for every query working on that field.

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Yes, they are.

shared_buffers is block-oriented, and stored in the same format as on-disk.

This is generally good for performance, since the decompression is very fast, and the compression means that more fits in shared_buffers. The only case it might hurt is if you have enough storage to fit the whole dataset in shared_buffers uncompressed too.

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  • Yes, I have a lot of memory dedicated to postgresql and some xml data of few megabytes. A lot of queryes are eating cps, so I'm going to uncompress this data. Thank you.
    – user_0
    Aug 21, 2015 at 13:55

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