Data Compression in C++

Please refer to the Data Compression page for a discussion of the advantages of in-memory and persistent database compression.

In-Memory Database Compression

For C++ in-memory database applications the APIs for managing data compression are exactly as for C applications. Please see the C API Data Compression page for details.

Persistent Database Compression

The method for enabling compression for a persistent database is to set the MCO_FILE_OPEN_COMPRESSED flag on the database file device. This is done when defining the memory devices in the McoSqlOpenParameters passed to as shown in the following code snippet:

    const int n_devices = 4;
    int main( int argc, char ** argv )
        mco_device_t dev[n_devices];
        McoSqlEngine engine;
        McoSqlOpenParameters params;
        dev[0].type       = MCO_MEMORY_CONV;
        dev[0].assignment = MCO_MEMORY_ASSIGN_DATABASE;
        dev[0].size       = DATABASE_SIZE;
        dev[0].dev.conv.ptr = (void*)malloc( DATABASE_SIZE );
        dev[1].type       = MCO_MEMORY_CONV;
        dev[1].assignment = MCO_MEMORY_ASSIGN_CACHE;
        dev[1].size       = CACHE_SIZE;
        dev[1].dev.conv.ptr = (void*)malloc( CACHE_SIZE );
        dev[2].type       = MCO_MEMORY_FILE;
        dev[2].assignment = MCO_MEMORY_ASSIGN_PERSISTENT;
        strcpy(dev[2], "persondb.dbs");
        dev[2].dev.file.flags = MCO_FILE_OPEN_COMPRESSED;
        dev[3].type       = MCO_MEMORY_FILE;
        dev[3].assignment = MCO_MEMORY_ASSIGN_LOG;
        strcpy(dev[3], "persondb.log");
        dev[3].dev.file.flags = MCO_FILE_OPEN_DEFAULT;
        params.databaseName = (char *)db_name;
        params.dictionary = persondb_get_dictionary();
        params.mainMemoryDatabaseSize = DATABASE_SIZE;
        params.mainMemoryPageSize = MEMORY_PAGE_SIZE;
        params.n_devices = n_devices;
        params.devices = dev;
        params.compressionLevel = 9;
        params.diskDatabaseMaxSize = 100*1024*1024;

Note that eXtremeDB implements LZ compression in two special file system libraries: mcofu98zip and mcofu98ziplog which are only available on Unix systems like Linux, MacOS and Solaris.

Data Compression for IoT Communications

For C++ IoT applications, the APIs for managing data compression in IoT communications are exactly as for C applications. Please see the C API Data Compression page for details.