Which query is producing this result?

An Administrator has been presented with these performance metrics from the DBQLOGTBL table for four queries:

The Administrator needs to identify which query is suspected to be causing a full table scan or large redistribution.

Which query is producing this result?
A . QRY_D because of CPU SKEW
B . QRY_C because of UII
C . QRY_B because of IO SKEW
D . QRY_A because of PJI

View Answer

Answer: C

Explanation:

IO SKEW refers to an uneven distribution of I/O operations across AMPs, which can occur during large redistributions or full table scans, as data needs to be read from or written to the entire table. High IO skew indicates that some AMPs are handling significantly more I/O than others, which is often a sign of inefficient data distribution or full table scanning.

QRY_B has an IO SKEW value of 2.76, which is much higher than the other queries, suggesting that it is likely performing a full table scan or large redistribution, as this would result in uneven I/O across AMPs.

CPU SKEW (as seen in QRY_D) could indicate an issue with CPU load balancing, but it doesn’t necessarily suggest a full table scan or redistribution.

UII (Utility Impact Index) and PJI (Product Join Index) are also metrics that might indicate query inefficiencies, but the high IO SKEW in QRY_B is the most direct indicator of a full table scan or large redistribution.

QRY_B is the query suspected of causing the full table scan or large redistribution due to its high IO SKEW value.