Setting Storage Performance

You can use the measurements returned from the MEASURE_LOCATION_PERFORMANCE function as input values to the SET_LOCATION_PERFORMANCE() function.

The following example shows how to set the performance of a storage location on v_vmartdb_node0004, using values for this location returned from the MEASURE_LOCATION_PERFORMANCE function. Set the throughput to 122 MB/second and the latency to 140 seeks/second. MEASURE_LOCATION_PERFORMANCE

=> SELECT SET_LOCATION_PERFORMANCE('/secondVerticaStorageLocation/','node2','122','140');

Sort Order Ranking by Location Performance Settings

After you set performance-data parameters, Vertica automatically uses performance data to rank storage locations whenever it stores projection columns.

Vertica stores columns included in the projection sort order on the fastest available storage locations. Columns not included in the projection sort order are stored on slower disks. Columns for each projection are ranked as follows:

• Columns in the sort order are given the highest priority (numbers > 1000).
• The last column in the sort order is given the rank number 1001.
• The next-to-last column in the sort order is given the rank number 1002, and so on until the first column in the sort order is given 1000 + # of sort columns.
• The remaining columns are given numbers from 1000–1, starting with 1000 and decrementing by one per column.

Vertica then stores columns on disk from the highest ranking to the lowest ranking. It places highest-ranking columns on the fastest disks and the lowest-ranking columns on the slowest disks.

Using Location Performance Settings with Storage Policies

You initially measure location performance and set it in the Vertica database. Then, you can use the performance results to determine the fastest storage to use in your storage policies.

• Set the locations with the highest performance as the default locations for critical data.
• Use slower locations as default locations for older, or less-important data. Such slower locations may not require policies at all, if you do not want to specify default locations.

Vertica determines data storage as follows, depending on whether a storage policy exists: