Database Management

Database Users

A CUBRID database user can have members with the same authorization. If authorization A is granted to a user, the same authorization is also granted to all members belonging to the user. A database user and its members are called a “group.”; a user who has no members is called a “user.”

CUBRID provides DBA and PUBLIC users by default.

  • DBA can access every object in the database, that is, it has authorization at the highest level. Only DBA has sufficient authorization to add, alter and delete the database users.
  • All users including DBA are members of PUBLIC. Therefore, all database users have the authorization granted to PUBLIC . For example, if authorization B is added to PUBLIC group, all database members will automatically have the B authorization.

databases.txt File

CUBRID stores information on the locations of all existing databases in the databases.txt file. This file is called the “database location file”. A database location file is used when CUBRID executes utilities for creating, renaming, deleting or replicating databases; it is also used when CUBRID runs each database. By default, this file is located in the databases directory under the installation directory. The directory is located through the environment variable CUBRID_DATABASES.

db_name db_directory server_host logfile_directory

The format of each line of a database location file is the same as defined by the above syntax; it contains information on the database name, database path, server host and the path to the log files. The following example shows how to check the contents of a database location file.

% more databases.txt

dist_testdb /home1/user/CUBRID/bin d85007 /home1/user/CUBRID/bin
dist_demodb /home1/user/CUBRID/bin d85007 /home1/user/CUBRID/bin
testdb /home1/user/CUBRID/databases/testdb d85007 /home1/user/CUBRID/databases/testdb
demodb /home1/user/CUBRID/databases/demodb d85007 /home1/user/CUBRID/databases/demodb

By default, the database location file is stored in the databases directory under the installation directory. You can change the default directory by modifying the value of the CUBRID_DATABASES environment variable. The path to the database location file must be valid so that the cubrid utility for database management can access the file properly. You must enter the directory path correctly and check if you have write permission on the file. The following example shows how to check the value configured in the CUBRID_DATABASES environment variable.

% set | grep CUBRID_DATABASES
CUBRID_DATABASES=/home1/user/CUBRID/databases

An error occurs if an invalid directory path is set in the CUBRID_DATABASES environment variable. If the directory path is valid but the database location file does not exist, a new location information file is created. If the CUBRID_DATABASES environment variable has not been configured at all, CUBRID retrieves the location information file in the current working directory.

Database Volume

The volumes of CUBRID database are classified as permanent volume, temporary volume and backup volume.

  • In the permanent volumes,
    • there are data volumes, that usually store permanent data, but can also store temporary data.
    • there are log volumes, that can be further classified as: one active log, archive logs and one background archiving log.
  • In the temporary volumes, only temporary data is stored.

For more details on volumes, see Database Volume Structure.

The following is an example of files related to the database when testdb database operates.

File name Size Purpose Classification Description
testdb 512MB
permanent
data
Database
volume
The firstly created volume when DB is created.
This volume stores permanent data (system, heap and index files).
This volume includes database meta information.
cubrid createdb uses by default the size specified by db_volume_size in cubrid.conf.
testdb_perm 512MB
permanent
data
Manually added volume using cubrid addvoldb utility
This volume stores permanent data (system, heap and index files).
testdb_temp 512MB
temporary
data
Manually added volume using cubrid addvoldb utility
This volume stores temporary data (query results, list files, sort files, join object hashes).
testdb_x003 512MB
permanent
data
Automatically created when database requires more space.
This volume stores permanent data (system, heap and index files).
testdb_x004 512MB
permanent
data
Automatically created when database requires more space.
This volume stores permanent data (system, heap and index files).
testdb_x005 512MB
permanent
data
Automatically created when database requires more space.
This volume stores permanent data (system, heap and index files).
testdb_x006 64MB
permanent
data
Automatically created when database requires more space.
This volume stores permanent data (system, heap and index files).
The size of volume is not maximized (yet).
testdb_t32766 512MB
temporary
data
Temporary
Volume
Automatically created when database requires more space.
This volume stores temporary data (query results, list files, sort files, join object hashes).
testdb_lgar_t 512MB
background
archiving
Log
volume
A log file which is related to the background archiving feature.
This is used when storing the archiving log.
testdb_lgar224 512MB
archive
Archiving logs are continuously archived and the files ending with three digits are created.
At this time, archiving logs from 001~223 seem to be removed normally by cubrid backupdb -r
option or the setting of log_max_archives in cubrid.conf. When archiving logs are removed,
you can see the removed archiving log numbers in the REMOVE section of lginf file.
testdb_lgat 512MB
active
Active log file
testdb_dwb 1MB
temporary
data
Double write
buffer
Double write buffer storage file, where flushed pages are written first.
  • Database volume file
    • In the table above, testdb, testdb_perm, testdb_temp, testdb_x003 ~ testdb_x006 are classified as the database volume files.
    • File size is determined by db_volume_size in cubrid.conf or the –db-volume-size option of cubrid createdb and cubrid addvoldb.
    • When database remains out of space, it automatically expands existing volumes and creates new volumes.
  • Temporary volume
    • Temporary volumes are usually used to store temporary data. They are automatically created and destroyed by database.
    • File size is determined by db_volume_size in cubrid.conf.
  • Log volume file
    • In the above, testdb_lgar_t, testdb_lgar224 and testdb_lgat are classified as the log volume files.
    • File size is determined by log_volume_size in cubrid.conf or the –log-volume-size option of cubrid createdb.
  • Double write buffer file * Double write buffer file is a storage area used to protect against I/O errors (partial writes). * Every data page write is first written into the buffer and then flushed to its location in the permanent data volumes. * During database reboot, partially written page is detected and replaced with the counterpart page in double write buffer. * The file size is determined by double_write_buffer_size in cubrid.conf. If set to zero, no file is created and double write buffer is disabled.

Note

Any data that has to be persistent over database restart and crash is stored in the database volumes created for permanent data purpose. The volumes store table rows (heap files), indexes (b-tree files) and several system files.

Intermediate and final results of query processing and sorting need only temporary storage. Based on the size of required temporary data, it will be first stored in memory (the space size is determined by the system parameter temp_file_memory_size_in_pages specified in cubrid.conf). Exceeding data has to be stored on disk.

Database will usually create and use temporary volumes to allocate disk space for temporary data. Administrator may however assign permanent database volumes with the purpose of storing temporary data using by running cubrid addvoldb -p temp command. If such volumes exist, they will have priority over temporary volumes when disk space is allocated for temporary data.

The examples of queries that can use temporary data are as follows:

  • Queries creating the resultset like SELECT
  • Queries including GROUP BY or ORDER BY
  • Queries including a subquery
  • Queries executing sort-merge join
  • Queries including the CREATE INDEX statement

To have complete control on the disk space used for temporary data and to prevent it from consuming all system disk space, our recommendation is to:

  • create permanent database volumes in advance to secure the required space for temporary data
  • limit the size of the space used in the temporary volumes when a queries are executed by setting temp_file_max_size_in_pages parameter in cubrid.conf (there is no limit by default).