The problems in PostGres DB are solved in MySQL to an extent. The design merits of MySQL are the following:

• The primary index has a mapping of key to an offset in the disk. But all secondary index tables have a mapping of key to the primary index’s key.

Primary index  
--------------------  
| key | Disk offset|  
--------------------  

Secondary index  
---------------------  
| key | primary key |  
---------------------  

• The drawback is that a lookup of the secondary table needs two hops.
• On the other hand, a change in a row only needs modification of the primary index. It avoids changing the secondary index for every change in row’s data
• MySQL replication uses logical information instead of data with physical information used in PostGres.
• Logs are compact compared to PG.
• MySQL manages its own cache, unlike PG that uses buffer cache.
• PG buffer cache use is inefficient since a read operation would have to land in the buffer cache and hence a context switch.
• PG uses a process per connection. It is expensive. MySQL uses threads for a connection and scales without too much resource consumption.