Glossary

Database-wide pages Adaptive Server uses to maintain the information about how each unit of 256 contiguous database pages is used.

A buffer is a structure that Adaptive Server uses to store physical disk pages while they are in memory. When a page is read into memory from disk, a buffer header is assigned to it. The header tracks the usage and the contents of the page image. Together, the page and the buffer header define a buffer.

An index in which the physical order of the data and the logical (indexed) order of the data is the same. Only one clustered index can exist on a table. See also “leaf level.”

A dbtable is a memory structure that tracks information about a database; for example whether the database is currently in use, whether it is in single-user mode, and and other data needed by a server task accessing the database.

The Adaptive Server error log file includes:

• Adaptive Server restart messages (including database recovery messages)

• Fatal error messages

• Error messages from the kernel

The name of this file varies; see the Adaptive Server installation and configuration guide for details.

The Backup Server has its own error log file where Backup Server error messages are written. Refer to “Backup Server Error Logging” in the System Administration Guide for details.

The SQL Monitor Server has its own error log file where SQL Monitor Server error messages are written. Refer to the Monitor Server Supplement for your platform for details.

The Replication Server has its own error log file where Replication Server error messages are written. Refer to the Replication Server Administration Guide for details.

The Navigation Server has its own error log file where Navigation Server error messages are written. Refer to the Navigation Server Reference Manual for details.

Every 256-page allocation unit is divided into 32 structures called extents, each containing 8 contiguous pages. Each extent contains information about those 8 contiguous pages, including a bitmap showing pages in use and a bitmap showing pages to be deallocated.

In a table, a column whose data values correspond to the values of a key column in another table.

The number Adaptive Server uses to uniquely identify (within a database) an index. The following table shows the index types:

The bottom of a clustered or nonclustered index. In a clustered index, the leaf level contains the actual data pages of the table.

The unique address for pages in the context of each database.

Buffers are grouped together to form Memory Address Space Segments (MASSes). A buffer cache consists of MASSes linked in MRU/LRU (most recently used/least recently used) chains.

An index that stores key values and points to data. The leaf level points to data rows rather than containing the data itself.

An Object Allocation Map (OAM) contains information about how space is allocated for Adaptive Server objects. A single OAM page holds information about up to 250 allocation pages (248 if the object is an IDENTITY column).

Each allocation page for an object has an entry in the OAM pages for that table or index. The OAM entry for each allocation page stores the number of used and unused data and index pages on that allocation page.

A maximum of 263 OAM pages are allowed, supporting a maximum of 65,535 allocation units for an object.

The number Adaptive Server uses to uniquely identify (within a database) an Adaptive Server object. If you know an object ID and you know the database the object is in, you can determine the object name. System tables have an object ID that is less than 100 and user tables have an object ID that is 100 or greater.

The column or combination of columns that uniquely identify a row.

A procedure executed on a different Adaptive Server from the Adaptive Server the user is logged into.

The data structures used to manage access to Adaptive Server objects. Session descriptors exist in three forms: user session descriptors (including worktable session descriptors), system session descriptors, and worktable session descriptors (separate from user session descriptors).

One of the data dictionary tables. System tables have an object ID that is less than 100. The system tables keep track of information about the Adaptive Server as a whole and about each user database. The master database contains some system tables that are not in user databases. The “Sybase Adaptive Server System Tables Diagram,” available through Sybase Customer Support, shows which system tables are in master only and which system tables are in all databases. For details about each system table, refer to the Adaptive Server Reference Supplement.

Timestamps are an attribute of each database. Each entry in the database transaction log is associated with a unique timestamp. Timestamps are used to order database activity; however, timestamps are not time-dependent.

A system table (syslogs) in which all changes to the database are recorded.

Actual offset on a device for a page within a database.