ER/Studio - Embarcadero Technologies Product Documentation

USING ER/STUDIO > DEVELOPING THE PHYSICAL MODEL
• No Sort: (NOSORT) If selected, specifies to not sort the data when the index is rebuilt.
• Reverse Byte Order: If selected, reverses the bytes of each column indexed (except the rowid) while keeping
the column order. By reversing the keys of the index, the insertions will be distributed across all leaf keys in the
index.
• Enable Compression: (COMPRESS) Select to enable index compression. Compression can repress duplication
of keys in non-unique indexes. For concatenated indexes (indexes with multiple columns), the compress option
can reduce the size of the index by more than half. For concatenated indexes (indexes with multiple columns),
compression can reduce the size of the index by more than half. The compress option allows you to specify the
prefix length for multiple column indexes.
• Prefix Length: This is the prefix length for multiple column indexes.
• Tablespace: Displays the tablespace on which the table index is stored.
• No Logging: Select, if you do not want the DLL operations to be logged in the redo file. This can reduce index
creation and updates by up to 30%.
• 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 Trans: (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. Initial Transactions
limit the minimum number of concurrent transactions that can update a data block to avoid the overhead of
allocating a transaction entry dynamically. Specify a higher value for indexes that may experience many
transactions updating the same blocks.
• Max Trans: (MAXTRANS) Specifies the maximum number of concurrent transactions that can update a data block
to avoid performance problems. 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.
• Parallel: Selects Oracle's parallel query option. You can achieve substantial performance gains by using Oracle's
parallel query option.
• Degrees: Specifies the number of query server processes that should be used in the operation.
• Instances: Specifies how you want the parallel query partitioned between the parallel servers.
• 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.
• Next Extent: (NEXT) Specifies the size in kilobytes of the next extent. You should monitor this figure against the
largest available chunk of free space in the tablespace. If a table cannot allocate its next extent, it will no longer
be able to extend and, therefore, cannot accept additional data.
• Pct Increase: (PCTINCREASE) Specifies the percentage by which the next extent should grow over the previous
extent's size. Be careful when setting Percent Increase because it magnifies how an object grows and, therefore,
can materially affect available free space in a tablespace.
• Min Extents: (MINEXTENTS) Specifies the number of extents to allocate when the segment is created. Controls
free space fragmentation by making sure that every used or free extent is at least as large as the value you
specify.
• Max Extents: (MAXEXTENTS) Specifies the maximum number of extents that Oracle can allocate to the index.
Once this limit is reached, Oracle prevents further growth of the cluster and cannot accept additional data.
Carefully monitor the number extents already allocated to the index with this limit.
EMBARCADERO TECHNOLOGIES > ER/STUDIO® 8.0.3 USER GUIDE 168