Thursday, December 29, 2011

SSIS Performance Counters

SQL Server Integration Services provide a set of performance counters. Among them the following few are helpful when you tune or debug your package:

·    Buffers in use

·    Flat buffers in use

·    Private buffers in use

·    Buffers spooled

·    Rows read

·    Rows written

“Buffers in use”, “Flat buffers in use” and “Private buffers in use” are useful to discover leaks. During package execution time, you will see these counters fluctuating. But once the package finishes execution, their values should return to the same value as what they were before the execution. Otherwise, buffers are leaked.

“Buffers spooled” has an initial value of 0. When it goes above 0, it indicates that the engine has started memory swapping. (“Set BLOBTempStoragePath and BufferTempStoragePath to Fast Drives”) to set Data Flow Task properties BLOBTempStoragePath and BufferTempStoragePath appropriately for maximal I/O bandwidth.

BLOBTempStoragePath and BufferTempStoragePath are two properties on Data Flow Task. They define where on the hard disk(s) to page buffer data to. BLOBs (text, next, image) are written to BLOBTempStoragePath. All other buffer data will be swapped to BufferTempStoragePath. See the figure below for where these two properties are exposed in designer.

Now what could cause a buffer to swap? There are two possible causes. The first one is when a memory allocation fails. The second one is when Windows signals the low memory resource notification event. Both will trigger SSIS to reduce its working set. SSIS does so by moving buffer data to disk.

When BLOBTempStoragePath is not set, the paths as defined by the system variables TEMP and TMP will be used. The same rule applies to BufferTempStoragePath.

For better performance, we recommend both BLOBTempStoragePath and BufferTempStoragePath point to fast drives. We also suggest that the drives for BufferTempStoragePath and BlobTempStoragePath be on separate spindles in order to maximize I/O throughput.

“Rows read” and “Rows written” show how many rows the entire Data Flow has processed. They give you an overall idea about the execution progress.

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