In-Memory Database vs Graph Database

Question

what are the new features provided by In-Memory Database in comparison with Graph Database ?

i.e:

• gridgain is In-Memory Database
• Neo4J is a graph database

Answer 1

That is not a question that can be answered the way you asked it. What are the differences between Computers and PCs?

Graph databases can be In-Memory databases. In-Memory is fast (obviously, because the data is stored in RAM) but for a given amount of money, you only get very finite RAM (much less storage than with HDDs/SSDs). The main advantage is that you avoid slow disk fetches and use the highly-parallel, multi-gigabit/s memory interface (that allows fast random access, in contrast to the seek behaviour of HDDs) plus the CPU-builtin caching.

What you should use depends (as always) on your usecase (and your money).