Prefetcher

Prefetcher

Prefetcher promotes the BLOBs in Hermes to improve the I/O performance. It predicts the next BLOBs to get and place them in a queue.

Algorithms - what to prefetch

• Size: Determine the size of a BLOB.
• Frequency: Count the number of times a BLOB has been read since its creation.
• Recency: Calculate the interval between the present and the last access time of a BLOB.
• Importance: Use the importance score set by user.

For example, smaller size BLOB will require the fewer number of target buffers and can be prefetched with higher precedence.

Alogirthms - when to prefetch

• Get API call.