Caching

OrientDB has several caching mechanisms that act at different levels. Look at this picture:

• Local cache is one per database instance (and per thread in multi-thread environment)
• Storage, it could cache depending on the implementation. This is the case for the Local Storage (disk-based) that caches file reads to reduce I/O requests
• Command Cache

How cache works?

Local Mode (embedded database)

When the client application asks for a record OrientDB checks:

• if a transaction has begun then it searches inside the transaction for changed records and returns it if found
• if the Local cache is enabled and contains the requested record then return it
• otherwise, at this point the record is not in cache, then asks for it to the Storage (disk, memory)

Client-Server Mode (remote database)

When the client application asks for a record OrientDB checks:

• if a transaction has begun then it searches inside the transaction for changed records and returns it if found
• if the Local cache is enabled and contains the requested record then return it
• otherwise, at this point the record is not in cache, then asks for it to the Server through a TCP/IP call
• in the server, if the Local cache is enabled and contains the requested record then return it
• otherwise, at this point the record is also not cached in the server, then asks for it to the Storage (disk, memory)

Record cache

Local cache

Local cache acts at database level. Each database instance has a Local cache enabled by default. This cache keeps the used records. Records will be removed from heap if two conditions will be satisfied:

1. There are no links to these records from outside of the database
2. The Java Virtual Machine doesn’t have enough memory to allocate new data

Empty Local cache

To remove all the records in Local cache you can invoke the invalidate() method:

db.getLocalCache().invalidate();

Disable Local cache

Disabling of local cache may lead to situation when 2 different instances of the same record will be loaded and OConcurrentModificationException may be thrown during record update even in single-thread mode.

To disable it use the system property cache.local.enabled by setting it at startup:

java ... -Dcache.local.enabled=false ...

or via code before to open the database:

OGlobalConfiguration.CACHE_LOCAL_ENABLED.setValue(false);