ER/Studio - Embarcadero Technologies Product Documentation

USING ER/STUDIO > DEVELOPING THE PHYSICAL MODEL
• Type: Select the partition type.
• Range: (PARTITION BY RANGE (column_name)) Select to store distinct ranges of data together, such as
dates. Searches can then be limited to partitions with data that is the correct age. Also, once historical data is
no longer useful, the whole partition can be removed.
• Hash: (PARTITION BY HASH (column_name) PARTITIONS count STORE IN tablespace)) Select
if there is no obvious range key or if range partitioning might cause uneven data distribution. If selected, the
Partition Count option is available.
• Partition Count: Click to launch the Hash Partition Editor where you can specify the number of subpartitions
and where to store them.
• Available Columns: Displays the columns available to add to a partition.
• Selected Columns: Displays the columns that make up the partition key. Guides how data is divided along the
partition boundaries. Typically, a partition key is date-based or based on a numerically ordered data grouping.
Use the left and right arrows to move columns to and from this grid.
• Up/Down buttons: Let you reorder the columns on the partition. The partition order can affect the access speed.
The most frequently accessed columns should be at the top of the partition list.
• Index Scope: Lets you specify the type of index partition to create.
• Local: (LOCAL) All index entries in the partition correspond to a one table partition (equi-partitioned). Supports
partition independence, allowing for more efficient queries.
• Global: (GLOBAL) The index in the partition can correspond to many table partitions. Does not support partition
independence and must be partitioned by range. If specified, you must specify the partition range values.
• Add: Click to launch the Index Partition Editor where you can add table partitions. For more information, see
Index Partition Editor for Oracle 8.x, 9i, 10g, and 11g Options.
• Edit: Click to launch the Index Partition Editor where you can add table partitions. For more information, see
Index Partition Editor for Oracle 8.x, 9i, 10g, and 11g Options.
Index Partition Editor for Oracle 8.x, 9i, 10g, and 11g Options
• Max Value: (VALUES LESS THAN (MAXVALUE)) Select to create a catch-all partition for values that exceed all
specified ranges. Otherwise, specify a High Value for the partition range.
• High Value: (VALUES LESS THAN (high value)) Specifies the ending value for the partition range.
• Pct Free: (PCTFREE) Specifies the maximum percentage of space in each data block to reserve for future
updates. This reserved space helps to avoid row migration and chaining caused by an update operation that
extends a data row's length. Tables that won’t be updated should have this value set to 0.
• Initial: (INITTRANS) Specifies the number of DML transactions for which space is initially reserved in the data
block header. Oracle stores control information in the data block to indicate which rows in the block contain
committed and uncommitted changes. The amount of history that is retained is controlled by this parameter. If too
many transactions concurrently modify the same data block in a very short period, Oracle may not have sufficient
history information to determine whether a row has been updated by a “too recent” transaction. Specify a higher
value for indexes that may experience many transactions updating the same blocks.
• Max Trans: (MAXTRANS) Once the space reserved by INITRANS is depleted, space for additional transaction
entries is allocated out of any available free space. Once allocated, this space effectively becomes a permanent
part of the block header. This parameter limits the number of transaction entries that can concurrently use data in
a data block and therefore limits the amount of free space that can be allocated for transaction entries in a data
block.
• Initial Extent: (INITEXTENT) Specifies the initial number of data blocks that Oracle should reserve. Oracle will
reserve the number of data blocks that correspond to the initial extent for that table’s rows.
EMBARCADERO TECHNOLOGIES > ER/STUDIO® 8.0.3 USER GUIDE 164