ActiveMQ -- kahadb of persistent mechanism

KahaDB

KahaDB Is a file based persistence database , from 5.4 The version starts to use by default , Be similar to redis Of AOF

Better fast persistence

To configure

see activemq.xml

stay activemq Under installation path ,activemq/data/hahadb, You can see db file

KahaDB Storage principle

KahaDB At present, it is the default storage method , It can be used in any scene , Improved performance and resilience .

The message store uses a Transaction log And a Indexes To store all his addresses .

KahaDB The data storage directory has 4 Class file plus 1 individual lock file .

db-1.log,db.data,db.free,db.redo,lock

• db-<number>.log Save message data ,number Indicates when the stored message reaches the predetermined size , The command mode of the file . When the file is full , A new file will be created ,number The value increases with it ,db-1.log,db-2.log,db-3.log… When no more messages are stored in the data file , Files will be deleted or archived

  It stores specific message data

• db.data Contains persistent B-Tree Indexes , Indexed the message data record （db-.log） The news of , He is the index file of the message , Essentially, B-Tree, Use B-Tree As an index, point to db-<number>.log The data stored inside

  Index file

• db-free Record db.data Free pages in the file , What you save is free pages id, Convenient for indexing , Start from the idle to ensure the continuity of the index , There are no fragments

• db.redo Message recovery , If kahaDB The message store starts after forced exit , Used to recover B-Tree Indexes

• lock File lock , Indicates the current acquisition kahaDB Read write permission broker, similar mysql The pessimistic lock of