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DML Tuning in .NET Get European Article Number 13 in .NET DML Tuning




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DML Tuning generate, create ean13 none on .net projects Microsoft Office Development. Microsoft Office 2000/2003/2007/2010 We looked in 5, Indexing ean13+5 for .NET and Clustering, at the overhead of indexes, and it s worth briefly revisiting the overhead here. Figure 14-1 shows the overhead of each additional index on a 1,000 row delete.

Each index adds substantial overhead to the delete because all matching index entries must be found and removed when removing the row. The overhead of deleting the indexes is, therefore, often greater than that of deleting the row itself. 5 includes guidelines on identifying indexes that are not used in queries and that might, therefore, be candidates for removal.

Remember that unique and foreign key indexes might be enforcing referential and data integrity; removing these in an attempt to improve DML throughput could jeopardize database integrity. TRIGGER OVERHEAD Triggers are PL/SQL blocks that execute when specified DML operations occur. The overhead of executing the PL/SQL is going to depend on the contents of the trigger and the rate of DML on the table involved, but there will always be some overhead.

. 16,316. 14,285. Number of Indexes 12,727. 10,719. 8,691. 6,671. 1 (PK Only). 1,191. 2,000. 4,000. 6,000. 8,000. 10,000. 12,000. 14,000. 16,000. 18,000. Logical Reads Required FIGURE 14-1 Overhead of indexes on DELETES. 14 Consider the following trigger, which maintains a UNIT_PRICE column that we might add to the SALES table: CREATE TRIGGER sales_iu_trg BEFORE INSERT OR UPDATE ON sales FOR EACH ROW WHEN (new.quantity_sold>0) BEGIN :new.unit_price := :new.

amount_sold/:new.quantity_sold; END; This is about as simple as a trigger gets, and yet it still creates a significant overhead on inserts and updates into the SALES table. Figure 14-2 compares the performance of a 2.

5 million row insert with and without the trigger. When the trigger was not present, the UNIT_PRICE column needed to be maintained within each SQL statement that INSERTED or UPDATED the SALES table. However, while the trigger automated this maintenance, the degradation in INSERT time was extremely significant.

. Even the simplest trigger Visual Studio .NET GTIN-13 creates a significant overhead on DML. Using triggers to maintain derived columns is convenient but not always efficient.

. No Trigger Trigger Elapsed Time (s). FIGURE 14-2 Overhead of a trigger on INSERT performance. DML Tuning In Oracle 11g, we can crea EAN-13 Supplement 2 for .NET te virtual columns defined by expressions on other columns within the table. Virtual columns can be used to implement some categories of denormalization and can do so with a lower overhead and greater reliability than triggers.

For instance, in 11g we can avoid creating a trigger and instead create a virtual column UNIT_PRICE defined as follows: ALTER TABLE sales ADD unit_price GENERATED ALWAYS AS ( CASE WHEN quantity_sold > 0 THEN ROUND(amount_sold/quantity_sold,2) END );. In Oracle 11g virtual colu mns can be used to create and maintain some derived columns without the overhead of trigger processing.. REFERENTIAL INTEGRITY Refe ean13+5 for .NET rential integrity constraints prevent foreign key columns from referring to nonexistent primary key values. For instance, the following constraint prevents the CUST_ID column in SALES from referring to a nonexistent customer: ALTER TABLE sales ADD CONSTRAINT fk1_sales FOREIGN KEY (cust_id) REFERENCES customers (cust_id) The presence of the foreign key constraint forces Oracle to check the CUSTOMER table for every row inserted into the SALES table.

Not surprisingly, this slows down inserts into SALES (see Figure 14-3). Similar overheads are involved during UPDATES and DELETEs..

Using referential integrit y constraints helps ensure self-consistency within your database and is generally recommended. However, be aware of the impact during INSERTs (and UPDATEs of foreign keys)..

14 . No Referential Integrity Referential Integrity Elapsed Time (s). FIGURE 14-3 Overhead of referential integrity on inserts. INSERT SPECIFIC OPTIMIZATIONS Oracle provides quite a fe GS1-13 for .NET w optimizations designed to speed up inserts, especially when you want to insert multiple rows. Array processing enables multiple rows to be inserted in a single operation.

Direct path inserts perform insert IO directly against the database files, bypassing the buffer cache. Multi-table inserts enable multiple tables to be involved in a single insert SQL statement. In Manual Segment Storage Management (MSSM) tablespaces, multiple freelists help avoid contention for the data blocks that are to receive the inserts.

Parallel DML although available for all DML statements is most often used with bulk insert operations.. ARRAY PROCESSING We first looked at array processing in 6, Application Design and Implementation, in which we discussed the use of array fetch and array insert. Array processing enables a single SQL to fetch or modify multiple rows in a single database call. Array processing can be applied to all DML statements, but it s most valuable during insert.

INSERTs add new rows into empty or nearly empty Oracle blocks,.
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