Major Objects

Overview

• Major Objects
  • Use Major Objects for fast in-memory handling of large amount of data that is thread-safe but must be persisted
  • We must support complex objects with simple keys, crud, and fast lookup by multiple keys.
  • Our most useful containers are vector, set (key in object) and map (<key,value> pair). Set can give us almost every positive feature, when used to store the PersistentIDObject class.
  • Use an unordered_set of const pointers to objects derived from PersistentIDObject
  • The default container should index by db_id primary key
  • Always use the db_id for foreign keys
  • Other containers can be created with alternate keys using object members; just define new hash functions.
• PersistentIDObject
  • Add a dirty flag to all objects, set to true on any change that must be persisted
  • Use an internal in-memory counter to generate the next db_id for a newly created object
  • This means that when creating new objects, there is NO NEED to access db, VERY IMPORTANT!
  • Use delayed-write tactics to write all dirty objects on idle time
• Memory Model
  • Use a Datastore manager (aka "MemoryModel") to hold sets
  • It can look up objects by any key, and strip away const to return a mutable object. NOTE that the user must not damage the key values!
  • Derive a class from the memory model for persistence; it can use any persistence method (local, remote, sql, nosql, etc.).
  • Make sure that the base MemoryModel class is concrete not abstract, thread-safe and self-contained; this makes parallel calculations trivial, helps scalability, etc.

Delete pattern

• find object iterator by id and pass it to parent containter delete method

           int64_t account_id;
           auto itba = p_user->findBrokerAccount(account_id);
           if (itba == p_user->accounts_.end() )
               return;
           p_user->deleteBrokerAccount(itba);

• container delete method passes object ref to Datastore method, deletes from memory, removes from container

bool AppUser::deleteBrokerAccount(AccountIt itba)
{
    BrokerAccount& ba = **itba;
    g_p_local->deleteBrokerAccount(ba);     // delete from db
    delete &ba;                             // delete from memory
    accounts_.erase(itba);                  // erase from container
}

• Datastore method deletes from db