Database¶

CrosDB Database is a collection of tables.

Steps to define a database

Decide where to store the database: on disk, on ramdisk or in memory.
Decide the database is accessed by single process or multiple proceses.
Use cross_dbCreate to create or open database.
Use Schema to define table scheam.
Decide Table Primary Key: fields list, index type.
Use cross_dbTblCreate to create or open table with schema defined above and provide the primary key.
Decide how many secondary indexes: fields list, index type, whether unique.
Use cross_dbIdxCreate to create table secondary index.

Storage Mode¶

On-Disk Database

Database is on persistent disk, survive with power cycle.
If you have data persistency requirements, please use this type. The performance is ver high.
You need use transaction to guarantee data integrity even power cycle happened.

RamDisk Database

Database is on ramdisk tmpfs ramfs(CROSS_RAMDISK), survive with process restart, lose after power cycle.
This is designed for process runtime databse and the transaction performance is higher than On-Disk database.
The performance is almost the same with In-Memory database.
For Linux embedded system, this is the prefered database as the database can be viewed and stayed there even process crashed.

In-Memory Database

Database is in memory(CROSS_INMEM), survie when process is runnig, lose after process terminates.
This is not recommented, but if you don't want the process runtime database visible, it's the solution.

Access Mode¶

Exclusive

Database is accessed exclusively by single process with best performance.

Shared

Databse is accessd by multiple process(CROSS_SHARED), then performance will be low as file lock is used to access DB which can recover lock when process crashed.

Note

Database is accessed exclusively by default.

Guide¶

Database is stored on disk by default.
If path(absoulte or relative) is not provided, DB is stored in current folder.

Example¶

#define CHECK(ret,str)  \
    if (ret < 0) {  printf (str": %s\n", cross_errMsg(ret)); return -1; }

cross_ret       ret;
cross_db_h      hDb;

// Create on disk database in current folder for single process access
ret = cross_dbCreate (&hDb, "ondiskdb", 0);
CHECK (ret, "Failed to create database");

// Create on disk database for multiple process access
ret = cross_dbCreate (&hDb, "cdb_data/shareddb", CROSS_SHARED);
CHECK (ret, "Failed to create database");

// Create ramdisk database for single process access
ret = cross_dbCreate (&hDb, "/tmp/cdb_data/mydb", CROSS_RAMDISK);
CHECK (ret, "Failed to create database");

// Create in memory database
ret = cross_dbCreate (&hDb, "imdb", CROSS_INMEM);
CHECK (ret, "Failed to create database");