- access method
- A set of server routines that the database server uses to
store and access the data in an index or a table. B-tree is the
default secondary access method. Some DataBlade modules have their
own access methods, with routines defined by the module.
See also primary access method, secondary access method.
- B-tree index
- A type of index that uses a balanced tree structure for efficient
record retrieval. B-tree indexes store key data in ascending or
descending order.
-
bounding box
- A rectilinear shape that completely contains the bounded object
or objects. Bounding boxes are usually stored as a set of coordinates
of the same dimensionality as the bounded object or objects.
- bottom-up build
- The default method that the R-tree access method uses when
creating an R-tree index. This method uses a fast bulk-loading algorithm
to create the index.
- branch page
- A location on a tree structure that has at least one page
below and one page above it. In an R-tree index, branch pages are
located in the intermediate levels, between the root page and leaf pages.
-
commutator function
- A Boolean function that accepts the same two arguments, in
reverse order, as another Boolean function, and returns the same result.
The query optimizer might choose the commutator function if it executes
more quickly in a given query than the specified function.
See also negator function.
- complex qualification
- A WHERE clause in a query in which
two or more logical operators are used on the same column on which
the R-tree index is defined.
- concurrency
- The ability of two or more processes to access the same database
simultaneously.
- data object
- The data that is stored in an R-tree indexed column of a table
and in the R-tree index itself.
-
dbspace
- A logical collection of one or more chunks within which you
store databases and tables. Because chunks represent specific regions
of disk space, the creators of databases and tables can control
where their data is physically located by placing databases or tables
in specific dbspaces.
See also sbspace.
- degenerate bounding box
- A bounding box in which one or more sides has a length of
0.
- expression based fragmentation
- A method of partitioning a table or index into fragments in which
the result of an expression determines the fragment in which a row
will reside. You fragment tables to logically distribute data and
thereby improve performance of queries that use the expression in
their WHERE clause.
- fillfactor
- An index parameter that specifies the percentage of an R-tree
index page that should be filled with entries when the R-tree access
method creates an R-tree index using the bottom-up build method.
- functional index
- An index that stores the result of executing a specified function
on a table column.
- INFORMIXDIR
- The Informix environment variable that specifies the directory
in which IBM Informix products are installed.
- interface
- In the DataBlade Developers Kit, a way to refer to a DataBlade
module within another DataBlade module. Because an interface creates
a dependency on another module, BladeManager ensures that the originating
module is registered before the module that contains the interface.
- key
- A unique identifier. A key is a column or combination of columns
whose value is unique for each row. Among the various keys available
are primary keys and foreign keys.
- leaf page
- A location on a tree structure that has at least one page
above it and no pages below it. In an R-tree index, leaf pages are
located in the final levels and contain data objects and row IDs.
- locking
- The process of temporarily limiting access to an object (database,
table, page, or row) to prevent conflicting interactions among concurrent processes.
Locking helps ensure data integrity. The database server guarantees
that, as long as the data is locked, no other program can modify
it.
- logical log
- An allocation of disk space managed by the database server
that contains records of all changes that were performed on a database
during the period the log was active. The logical log is used to
roll back transactions, recover from system failures, and restore
databases from backups.
- loose bounding box
- A bounding box that is intentionally larger than its data
object.
- multi-representational data type
- A data type whose storage location varies depending on the size
of the data.
-
negator function
- A Boolean function that accepts the same arguments in the
same order as another Boolean function, but returns the Boolean complement.
The query optimizer might choose the negator function if it executes
more quickly in a given query than the specified function.
See also commutator function.
-
operator class
- The set of operators that the database server associates with
a secondary access method. When an index is created, it is associated with
a particular operator class.
-
primary access method
- A set of routines that perform table operations such as inserting, deleting,
updating, and searching data. The database server provides a virtual
table interface (VTI), with which advanced
users can create primary access methods for virtual tables.
- purpose function
- One of a set of functions that an access method uses to create,
search, and drop indexes, and to insert entries into an index, delete from
an index, and so on.
- query optimizer
- A server facility that estimates the most efficient plan for
executing a query in the database server. The optimizer considers
the CPU cost and the I/O cost
of executing a plan.
- registration
- The process of executing SQL statements
to create DataBlade module objects or individual user-defined routines
in a database and giving the database server the location of the associated
shared object file. Registration makes a DataBlade module available
for use by client applications that open that database.
- root page
- The topmost level in a tree structure. In an R-tree index,
the root page can have zero or more branch pages or leaf pages below
it, depending on the size of the R-tree index.
- round-robin fragmentation
- A method of partitioning a table or index into fragments in which
the database server balances the number of rows in each fragment.
As more rows are inserted, the database server determines the fragment
in which they should reside.
-
routine signature
- The information that the database server uses to identify
a routine. The signature of a routine includes the type of the routine
(function or procedure), the routine name, the number of parameters,
the data types of the parameters, and the order of the parameters.
- row ID
- An integer that defines the physical location of a row. The
database server assigns a unique row ID to
each row in a nonfragmented table. If you want to access data in
a fragmented table by row ID, you must
create a row ID column.
- R-tree index
- A type of index that uses a tree structure based on overlapping
bounding rectangles to speed access to spatial and multidimensional
data types.
-
sbspace
- A logical storage area that contains one or more chunks that
store only smart large-object data.
-
secondary access method
- A set of server functions that build, access, and manipulate
an index structure: for example, a B-tree, an R-tree, or an index
structure that a DataBlade module provides. Typically, a secondary
access method speeds up the retrieval of data.
When an SQL query uses an index created
using a secondary access method, it accesses the index using the
functions defined in the operator class belonging to that access
method.
See also operator class.
- selectivity
- The characteristic of a query that determines the fraction
of the total number of rows that the query returns. The more selective
the query, the smaller the fraction.
- signature
- See routine signature.
- strategy functions
- The functions for which the query optimizer can use an index
scan in a query. You specify these functions in the operator class with
which the index is created.
- support functions
- The functions that an access method uses internally to build
and maintain an index structure. They are not available for use
in SQL queries.
- system catalog
- A group of database tables that contain information about
the database itself, such as the names of tables or columns in the
database, the number of rows in a table, the information about indexes
and database privileges, and so on.
- temporary dbspace
- A dbspace used to store temporary tables or other data that
need not be saved between sessions.
- user-defined data type
- A data type that is not built-in, namely, a collection data
type, row data type, opaque data type, or distinct data type.
-
user-defined routine
- A routine, written in one of the languages that Dynamic Server supports,
that provides added functionality for data types or encapsulates
application logic.
- variant routine
- A routine that can return different values when it is invoked
with the same arguments.