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Re: text vs varchar
Posted by: Øystein Grøvlen
Date: May 02, 2016 04:37AM

Hi Rick,

No, I am referring to that when a row is read from storage engine into MySQL server, the size of the buffer allocated for the row is the maximum row size. However, only the column values that are actually needed will be copied into this buffer. So more memory will be allocated than if TEXT was used instead of VARCHAR.

I did not consider temporary tables in my answer since the question stated that such columns would only be fetched by look-up on primary key. If so, temporary tables should not apply. It is also the case that for temporary tables with VARCHAR(n) columns where n > 512, MEMORY will not be used. Hence, with respect to temporary tables, behavior should be the same regardless of whether column is VARCHAR(4000) and TEXT.

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway

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