Storage Memory Hierarchy in database

Let’s discuss the storage memory hierarchy based on speed of access used in database systems.

CPU:

  • It is very fast.
  • Stores the data in registers.
  • Processes the data values, evaluates the arithmetics expressions, computes the address for data values, etc.

Cache:

  • RAM is thousands time slower than CPU.
  • cache is an intermediate storage between RAM and CPU.
  • Helps to fetch the data from RAM in advance.
  • Gives CPU an illusion of having a faster Main memory storage.
  • Faster than RAM but slower than CPU.

memory_hierarchypng

RAM:

  • Stores frequently used program instructions to increase the general speed of a system.
  • Uses an optimistic approach of prefetching the data from disk drives.
  • Faster then Hard disk, but slower than Cache.
  • The smallest storage unit is 1 byte.

SSD:

  • Used as permanent storage for systems that need faster storage access.
  • Offers 10X speed compared to magnetic disk drives.
  • Costlier than RAM, but cheaper than magnetic disk drives.
  • Used by some inmemory databases and cloud based file systems.

Magnetic disk drives:

  • Has a few rigid rapidly rotating disks (platters) coated with magnetic material.
  • These are cheaper and widely used to store persistent data.
  • Read and write are in the volumn of blocks.

Tape drives are obsolete. Need not discuss them now.