How do I decide where I should locate my TimesTen database files?

Question

I am setting up a TimesTen In-Memory database and I am looking for guidance on the storage and location that I should use for the database's persistence files.

Answer 1

A TimesTen database consists of two types of file; checkpoint files (two) and transaction log files (always at least one, usually many).

There are 3 criteria to consider:

a) Data safety and availability (regular storage versus RAID). The database files are critical to the operation of the database and if they become inaccessible or are lost/damaged then your database will become inoperable and you will likely lose data. One way to protect against this is to use TimesTen's built in replication to implement high availability but even if you do that you may also want to protect your database files using some form of RAID storage. For performance reasons RAID-1 is preferred over RAID-5 or RAID-6. Use of NFS storage is not recommended for database files.

b) Capacity. Both checkpoint files are located in the same directory (Datastore attribute) and hence in the same filesystem. Each file can grow to a maximum size of PermSize + ~64 MB. Normally the space for these files is pre-allocated when the files are created, so it is less likely you will run out of space for them. By default, the transaction log files are also located in the same directory as the checkpoint files, though you can (and almost always should) place them in a different location by use of the LogDir attribute. The filesystem where the transaction logs are located should have enough space such that you never run out. If the database is unable to write data to the transaction logs it will stop processing transactions and operations will start to receive errors.

c) Performance. If you are using traditional spinning magnetic media, then I/O contention is a significant concern. The checkpoint files and the transaction log files should be stored on separate devices and separate from any other files that are subject to high levels of I/O activity. I/O loading and contention is less of a consideration for SSD storage and usually irrelevant for PCIe/NVMe flash storage.