What does LOCAL RESEGMENT GROUPS mean?

Thomas_Zhenhua_

When we do EXPLAIN <query>, sometimes it shows LOCAL RESEGMENT GROUPS.  I'm just wondering what it means.  Thanks.

Rahul_Choudhary

Hi Thomas

When you run a query that references more than one table, HP Vertica may need to do one or both of the following operations to join the tables together:
1) Sort the data
2) Resegment the data

Local resegment groups are formed by resegmenting the data during the query execution with a node so that more parallelism can be exploited by each core can work on each of the small segment of the data. 

I hope this answers your question.

Regards
Rahul

Vijaya_Bhaskar_

Rahul, 

  Could you please explain for "LOCAL RESEGMENT GROUPS" and reason for joins in Plan with SQL involves one Table .

EXPLAIN SELECT COUNT(distinct customer_key) AS cntd_cust     store_key,

        COUNT(DISTINCT product_key) AS cntd_prod,          COUNT(DISTINCT promotion_key) AS cntd_promo,          SUM(sales_dollar_amount) AS sum_sales_dollar,          SUM(cost_dollar_amount) AS sum_cost_dollar   FROM store.store_sales_fact   GROUP BY store_key   ORDER BY cntd_cust DESC   LIMIT 25;

https://my.vertica.com/docs/7.0.x/HTML/index.htm#Authoring/AdministratorsGuide/EXPLAIN/PartiallySort...