There are some good high level discussions on the various database architectures for implementing software as a service.  I’m on going to duplicate that.  Instead, this article is going to highlight some of the issues and tradeoffs when multiple tenants (customers of the software service provider) are put into one database.   The core of the problem is having multiple tenants in one set of database tables can make queries that select data for only one customer much slower. 

First, I’m testing on a new system, one with 32 gig of memory.  Currently,  the innodb_buffer_pool_size set to 28 gig.   I’m using the same size tables as previously, both Sale and SaleTenant have 120 million rows and are about 27 and 28 gig respectively.  This means that the tables fit into memory, so the following tests do not have an IO component.  Not perfect, but it shouldn't make a difference in the …