Where collect stats are stored in Teradata?

Collect Stats in Teradata collect the statistics for one or even multiple columns of the base table specified. These statistics include the hash index, a join index, etc. Primarily its the collection of the statistical profile of the required columns and the same gets stored in a data dictionary.

How can I see my stats in Teradata?

You can view the collected statistics using HELP STATISTICS command.

How do you collect table statistics?

When a column specified for ANALYZE_STATISTICS is first in a projection’s sort order, the function reads all data from disk to avoid a biased sample.

  1. Collecting Table Statistics.
  2. Analyze All Database Tables.
  3. Analyze a Single Table.
  4. Analyze Table Columns.
  5. Data Collection Percentage.
  6. Sampling Size.

Can we collect stats on view in Teradata?

The Statistics Collection view lets you collect statistics on table columns and indexes. Collecting statistics on columns or indexes is important to producing query plans.

Can stats be collect on volatile table in Teradata?

You can run collect statistics on a volatile table. CHECK constraints, DEFAULT values are not allowed in the volatile table.

Why do we use collect stats in Teradata?

The COLLECT STATISTICS (Optimizer form) statement collects demographic data for one or more columns of a base table, hash index, or join index, computes a statistical profile of the collected data, and stores the synopsis in the Data Dictionary.

How do you drop stats in Teradata?

To drop all the stats defined on a table, use the following syntax, DROP STATS [ON]

Why do we need to collect stats in Teradata?

It is recommended to collect stats on non unique secondary indexes(NUSI) for optimizer to know total number of rows in NUSI subtable and make better decisions regarding the cost savings. It is recommended to collect stats on non-indexed columns that are frequently used in ‘WHERE’ clause and equi-joins.

Where are volatile tables stored Teradata?

Volatile tables are always created in the login user space, regardless of the current default database setting. That is, the database name for the table is the login user name. Space usage is charged to login user spool space. Each user session can materialize as many as 1000 volatile tables at a time.

What are column statistics in Teradata?

Collected statistics about columns are stored in intervals of histograms and as so-called summary statistics for information concerning the whole table. Teradata tries to store approximately the same number of different values in each interval. A column statistic can be a single column or a combination of columns.

How many intervals are there in Teradata?

Teradata uses only the number of intervals that are really needed. If there are only 10 different values in a column, only 10 intervals will be created for the corresponding statistics; of course, we can reduce the number of intervals at any time, but this rarely makes sense.

How does Teradata optimizer work?

Teradata optimizer comes up with an execution strategy for every SQL query. This execution strategy is based on the statistics collected on the tables used within the SQL query. Statistics on the table is collected using COLLECT STATISTICS command.

How to determine SQL query performance in Teradata?

Several parameters can help us in understanding SQL Query Performance in Teradata. I consider AMPCPUTime, TotalIOCount, SpoolUsage as three main parameters to determine SQL Query performance. Say, you are executing multiple queries in Teradata sequentially.