Projection parameters

The following configuration parameters help you manage projections.

Query the CONFIGURATION_PARAMETERS system table to determine what levels (node, session, user, database) are valid for a given parameter.

AnalyzeRowCountInterval

Specifies how often Vertica checks the number of projection rows and whether the threshold set by ARCCommitPercentage has been crossed.

For more information, see Collecting database statistics.

Default: 86400 seconds (24 hours)

ARCCommitPercentage

Sets the threshold percentage of difference between the last-recorded aggregate projection row count and current row count for a given table. When the difference exceeds this threshold, Vertica updates the catalog with the current row count.

Default: 3 (percent)

ContainersPerProjectionLimit

Specifies how many ROS containers Vertica creates per projection before ROS pushback occurs.

Caution

Increasing this parameter's value can cause serious degradation of database performance. Vertica strongly recommends that you not modify this parameter without first consulting with Customer Support professionals.

Default: 1024

MaxAutoSegColumns

Specifies the number of columns (0 –1024) to use in an auto-projection's hash segmentation clause. Set to 0 to use all columns.

Default: 8

MaxAutoSortColumns

Specifies the number of columns (0 –1024) to use in an auto-projection's sort expression. Set to 0 to use all columns.

Default: 8

RebalanceQueryStorageContainers

By default, prior to performing a rebalance, Vertica performs a system table query to compute the size of all projections involved in the rebalance task. This query enables Vertica to optimize the rebalance to most efficiently utilize available disk space. This query can, however, significantly increase the time required to perform the rebalance.

By disabling the system table query, you can reduce the time required to perform the rebalance. If your nodes are low on disk space, disabling the query increases the chance that a node runs out of disk space. In that situation, the rebalance fails.

Default: 1 (enable)

RewriteQueryForLargeDim

If enabled (1), Vertica rewrites a SET USING or DEFAULT USING query during a REFRESH_COLUMNS operation by reversing the inner and outer join between the target and source tables. Doing so can optimize refresh performance in cases where the source data is in a table that is larger than the target table.

Important

Enable this parameter only if the SET USING source data is in a table that is larger than the target table. If the source data is in a table smaller than the target table, then enabling RewriteQueryForLargeDim can adversely affect refresh performance.

Default: 0

SegmentAutoProjection

Determines whether auto-projections are segmented if the table definition omits a segmentation clause. You can set this parameter at database and session scopes.

Default: 1 (create segmented auto projections)