Question

Is there any difference between speed of fetching data if dynamic rows is moved towards end.

example : int , int , int , text is better than int int text int ?

my lead has informed me about this fact , how ever no such information is getting from internet ? please help ?

Answer 1

This is due to data alignment. INT takes 4 bytes, so 32-bit (equivalent to 4 bytes) processors will work with data in 4 byte sequences. Being able to pull off the data in an order that best suits the processor will lead to faster results and better performance.

Reference: http://en.wikipedia.org/wiki/Data_structure_alignment

Now, this is a problem often found in transferring data over a communication channel (because certain compilers will typically optimize your data structure by adding a reserved byte to 4-byte align certain members). However, MySQL also takes 4-byte alignment into account with NDBCLUSTER engines. This means that by placing your TEXT structure in between the INT values, you force more data retrieval than necessary.

Thus:

INT INT INT INT TEXT will process faster than INT INT TEXT INT INT as the processor can retrieve 16-bytes (the four INT) immediately without worrying about the size of TEXT.

For more details, see the MySQL documentation:

http://dev.mysql.com/doc/refman/5.5/en/storage-requirements.html