Hp ProLiant DL980 G7 Server User Manual download pdf (Page 59)

where the SQL Server is the main (or only) application running. HP ESO recommends and displays

this flag for non-SAP instances only.

Trace flag 1117

Trace flag 1117 determines how the SQL Server automatically extends (grows) data files in a file

group when automatic file growth is needed. Enable trace flag 1117 to cause the SQL Server to

automatically grow all of the files at the same time. Otherwise, the files will automatically grow in

round-robin fashion.

Trace flag 1118

Trace flag 1118 is used to help alleviate allocation bitmap contention in tempdb when under a

heavy load of small temp table creation and deletion.

Trace flag 2371

Trace flag 2371 is used to address the well-known problem caused by the current 20% threshold

that determines when automatic statistics updates occur. The statistics keep track of the number of

changes made to a table. The threshold is the percentage of the number of rows in the table. When

the number of changes exceed 20% of the number of rows in the table, the statistics are

automatically updated. For large applications with correspondingly large tables, this could mean

that automatic updates would not occur often enough to accurately reflect current statistics. As a

result, administrators would have to manually update the statistics (using a query plan, for example).

Because the manual updates usually require excessive I/O, this was not optimal for many

applications. The 2371 trace flag changes the threshold from a fixed-rate of 20% to a dynamic

rate based on the table size. The higher the number of rows in the table, the lower the threshold

will become to trigger an update of the statistics. Enable the 2371 trace flag to prevent the need

for manually updating the statistics. HP ESO recommends and displays this flag for SAP instances

only.

NOTE: To prevent small tables from being updated too frequently, automatic updates require a

minimum of 500 rows in a static table and 6 rows in a temp table.

Trace flag 2549

The DBCC CHECKDB checks the logical and physical integrity of all objects in the specified database.

The command builds an internal list of pages to read per unique disk drive across all database

files. The logic determines unique disk drives based on the drive letter of the physical file name of

each file. If the underlying disks are actually unique when the drive letters are not, the DBCC

CHECKDB command treats these database files as residing on one disk. Enable the trace flag to

optimize the CHECKDB process by treating each database file as residing on a separate, unique

disk drive. Do not use this trace flag unless you know that each file is based on a unique physical

disk. HP ESO recommends and displays this flag for SAP instances only.

Trace flag 2562

By default, the DBCC CHECKDB command tries to minimize the amount of tempdb resources

required to check the entire database. The command does this by breaking up the database into

batches. This reduces the number of indexes or "facts" that it generates. Trace flag 2562 implements

the following changes:

• Forces the DBCC CHECKDB command to run all processing in a single batch regardless of the

number of indexes in the database.

• Improves the internal process for determining which pages to read from the database. This

reduces contention on the DBCC_MULTIOBJECT_SCANNER latch, helping avoid such errors

as:

Timeout occurred while waiting for latch: class ‘DBCC_MULTIOBJECT_SCANNER’.

Optimizations pages: Viewing and controlling optimization recommendations 59

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