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Amazon Redshift
Database Developer Guide (API Version 2012-12-01)

STL_HASHJOIN

Analyzes hash join execution steps for queries.

This table is visible to all users. Superusers can see all rows; regular users can see only their own data. For more information, see Visibility of Data in System Tables and Views.

Table Columns

Column Name Data Type Description
userid integer ID of the user who generated the entry.
query integer Query ID. The query column can be used to join other system tables and views.
slice integer Number that identifies the slice where the query was running.
segment integer Number that identifies the query segment.
step integer Query step that executed.
starttime timestamp Time in UTC that the query started executing, with 6 digits of precision for fractional seconds. For example: 2009-06-12 11:29:19.131358.
endtime timestamp Time in UTC that the query finished executing, with 6 digits of precision for fractional seconds. For example: 2009-06-12 11:29:19.131358.
tasknum integer Number of the query task process that was assigned to execute the step.
rows bigint Total number of rows that were processed.
tbl integer Table ID.
num_parts integer Total number of partitions that a hash table was divided into during a hash step. A hash table is partitioned when it is estimated that the entire hash table might not fit into memory.
join_type integer The type of join for the step:
  • 0. The query used an inner join.

  • 1. The query used a left outer join.

  • 2. The query used a full outer join.

  • 3. The query used a right outer join.

  • 4. The query used a UNION operator.

  • 5. The query used an IN condition.

  • 6. This information is for internal use only.

  • 7. This information is for internal use only.

  • 8. This information is for internal use only.

  • 9. This information is for internal use only.

  • 10. This information is for internal use only.

  • 11. This information is for internal use only.

  • 12. This information is for internal use only.

hash_looped character(1) This information is for internal use only.
switched_parts character(1) Indicates whether the build (or outer) and probe (or inner) sides have switched.

Sample Queries

The following example returns the number of partitions used in a hash join for query 720.

Copy
select query, slice, tbl, num_parts from stl_hashjoin where query=720 limit 10;
Copy
query | slice | tbl | num_parts -------+-------+-----+----------- 720 | 0 | 243 | 1 720 | 1 | 243 | 1 (2 rows)