I'm dealing with blobs of up to - I estimate - about 100 kilo bytes in size. The data is compressed already.

Storage engine: InnoDB on MySQL 5.1

Frontend: PHP (Symfony with Propel ORM)

Some questions:

• I've read somewhere that it's not good to update blobs, because it leads to reallocation, fragmentation, and thus bad performance. Is that true? Any reference on this?

• Initially the blobs get constructed by appending data chunks. Each chunk is up to 16 kilo bytes in size. Is it more efficient to use a separate chunk table instead, for example with fields as below?

  parent_id, position, chunk

  Then, to get the entire blob, one would do something like:

  SELECT GROUP_CONCAT(chunk ORDER BY position) FROM chunks WHERE parent_id = 187

  The result would be used in a PHP script.

• Is there any difference between the types of blobs, aside from the size needed for meta data, which should be negligible.