Re: Why could different data in a table be processed with different performance?

[Fabio Pardi]

On 09/21/2018 08:28 AM, Vladimir Ryabtsev wrote:

>> but you say you observe a difference even after dropping the cache.
> No, I say I see NO significant difference (accurate to measurement
> error) between "with caches" and after dropping caches. And this is
> explainable, I think. Since I read consequently almost all data from the
> huge table, no cache can fit this data, thus it cannot influence
> significantly on results. And whilst the PK index *could* be cached (in
> theory) I think its data is being displaced from buffers by bulkier
> JSONB data.
> 
> Vlad

I think this is not accurate. If you fetch from an index, then only the
blocks containing the matching records are red from disk and therefore
cached in RAM.

regards,

fabio pardi