What are practical differences between `REPLACE` and `INSERT … ON DUPLICATE KEY UPDATE` in MySQL?

Question

What I need is to set the values of all the fields of a record with a particular key (the key is composite actually), inserting the record if there is no record with such a

Answer 1

To answer the question in terms of performance, I did a test using both the methods

Replace Into involves:
1.Try insert on the table
2. If 1 fails, delete row and insert new row

Insert on Duplicate Key Update involves:
1.Try insert on table
2.If 1 fails, update row

If all the steps involved are inserts, there should be no difference in performance. The speed has to depend on the number of updates involved. Worst case is when all the statements are updates

I have tried both the statements on my InnoDB table involving 62,510 entries (only updates). On camparing speeds:
Replace Into: 77.411 seconds
Insert on Duplicate Key Update: 2.446 seconds

Insert on Duplicate Key update is almost 32 times faster.

Table Size: 1,249,250 rows with 12 columns on an Amazon m3.medium