Database Volume Structure

The following diagram illustrates the CUBRID database volume structure. As you can see, the database is divided into three volumes: permanent, temporary and backup. This chapter will examine each volume and its characteristics.

Permanent Volume

Permanent volume is a database volume that exists permanently once it is created. Its types include generic, data, temp, index, control, active log and archive log.

Generic Volume

For efficient management, the volume type to be added to the database can be specified as one of the followings: data, temp or index. If data usage is not specified, it is specified as a generic volume.

Data Volume

Data volume is a space for storing data such as instances, tables and multimedia data.

Temp Volume

Temp volume is a space where the intermediate and final results of query processing and sorting are temporarily stored. It is also called the permanent temp volume to distinguish it from the temporary temp volume that will be described below. The temp volume is a permanently-occupied space, meaning that data in the space is temporary stored and later destroyed. Therefore, when CUBRID restarts, the data in the temp volume space is initialized and the related log information is removed.

Examples of queries that can use permanent temp volume or temporary temp volume are as follows:

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

When executing the queries above, the temp volume is used after exhausting the memory space (the space size is determined by the system parameter temp_file_memory_size_in_pages specified in cubrid.conf) assigned to store SELECT results or sort the data. The order in which the storage space is used to store the results of query processing and sorting is as follows: When the current storage space is exhausted, the next storage space is used.

temp_file_memory_size_in_pages memory secured by the system parameter

1. Permanent temp volume
2. Temporary temp volume (for details, see the below)

Index Volume

Index volume is a space that holds the index information for query processing or integrity constraint checks.

Control File

The control file contains the volume, backup and log information in the database.

• Volume Information: The information that includes names, locations and internal volume identifiers of all the volumes in the database. When the database restarts, the CUBRID reads the volume information control file. It records a new entry to that file when a new database volume is added.
• Backup Information: Locations of all the backups for data, index, and generic volumes are recorded to a backup information control file. This control file is maintained where the log files are managed.
• Log Information: This information contains names of all active and archive logs. With the log information control file, you can verify the archive log information. The log information control file is created and managed at the same location as the log files.

Control files include the information about locations of database volumes, backups and logs. Since these files will be read when the database restarts, users must not modify them arbitrarily.

Active Log

Active log is a log that contains recent changes to the database. If a problem occurs, you can use active and archive logs to restore the database completely up to the point of the last commit before the occurrence of the fault.

Archive Log

Archive log is a volume to store logs continuously created after exhausting available active log space that contains recent changes. If the value of system parameter log_max_archives is larger than 0, the archive log volume will be generated only after exhausting available active log volume space. The number of archive log files are kept on the storage by setting the value of log_max_archives. The unnecessary archive log files should be deleted for getting the free space by the configuration of log_max_archives, but this value should be set properly to use for restoring the database.

To get more information on the above, see Managing Archive Logs.

Note To get information on the conditions in which archive log can be deleted, see Managing Archive Log.

Background Archive Log

Background archive log is a volume used in the background with log archiving temporarily before creating archive logs. It is created as the same volume size as active log and stored.

Temporary Volume

Temporary volume has the opposite meaning to the permanent volume. That is, the temporary volume is a storage created only when the accumulated data exceeds the space specified by the user as the permanent volume. The temporary volume is destroyed when the server process terminates. One of such volumes created or destroyed temporarily is the temporary temp volume.

Temporary Temp Volume

Temporary temp volume is a temporary volume created temporarily by the system after exhausting the space specified as the permanent temp volume, whereas the temporary volume belongs to the permanent volume with the permanent space specified. Because cost to create a temporary temp volume is high, DBA should assign an appropriate size of volume depending on situation to enhance performance.

DBA should consider space where temporary temp volume can be created when creating a database. Once temporary temp volume is created, it is maintained until a database restarts and its size cannot be reduced. It is recommended to make temporary temp volume automatically delete by restarting a database if its size is too big.

• File name of the temporary temp volume: The file name of the temporary temp volume of CUBRID has the format of db_name_tnum, where db_name is the database name and num is the volume identifier. The volume identifier is decremented by 1 from 32766.
• Configuring the temporary temp volume size: The number of temporary temp volumes to be created is determined by the system depending on the space size needed for processing transactions. However, users can limit the temporary temp volume size by configuring the temp_file_max_size_in_pages parameter value in the system parameter configuration file (cubrid.conf). The default value is -1, which means it can be created as long as free space is available. If it is configured to 0, the temporary temp volume will not be created even after exhausting the permanent temp volume.
• Configuring storing location of the temporary temp volume: By default, the temporary temp volume is created where the first database volume was created. However, you can specify a different directory to store the temporary temp volume by configuring the temp_volume_path parameter value.
• Deleting the temporary temp volume: The temporary temp volume exists temporarily only while the database is running. Therefore, you must not delete the temporary temp volume when running servers. The temporary temp volume is deleted if database servers are normally terminated while it is deleted when the servers restart if database servers are abnormally terminated.

Backup Volume

Backup volume is a database snapshot; based on such backup and log volumes, you can restore transactions to a certain point of time.

You can use the cubrid backupdb utility to copy all the data needed for database restore, or configure the backup_volume_max_size_bytes parameter value in the database configuration file (cubrid.conf) to adjust the backup volume partitioning size.