What is the full meaning of the event in query_events?

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sarah
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What is the full meaning of the event in query_events?

Post by sarah » Fri Apr 11, 2014 7:58 am

Hi,

Does anyone know what the following events from the query_events table are in detail? Is there anywhere in the documentation that explains them fully? Which ones are bad, good, ok :?: :?: :?:

Code: Select all

vertica=> select distinct event_type, event_description from query_events order by 1, 2;
              event_type              |                                              event_description                                              
--------------------------------------+-------------------------------------------------------------------------------------------------------------
 DELETE WITH NON OPTIMIZED PROJECTION | Deleting rows in a projection required the slow path
 GROUPBY PUSHDOWN                     | The optimizer pushed GroupBy past a Join
 GROUP_BY_PREPASS_FALLBACK            | In-memory prepass disabled due to ineffectiveness.
 GROUP_BY_SPILLED                     | GROUP BY key set did not fit in memory, using external sort grouping.
 MEMORY LIMIT HIT                     | The optimizer used all of its allocated memory while planning
 MERGE_CONVERTED_TO_UNION             | Merge converted to union, followed by sort.
 NO GROUPBY PUSHDOWN                  | The optimizer couldn't push GroupBy past Join
 NO HISTOGRAM                         | The optimizer encountered a predicate on a column for which it does not have a histogram
 PARTITIONS_ELIMINATED                | Some storage containers will not be processed because they contain no relevant data.
 PREDICATE OUTSIDE HISTOGRAM          | The optimizer encountered a predicate that was false for the entire histogram.
 RESEGMENTED_MANY_ROWS                | Many rows were resegmented during plan execution.
 RLE_OVERRIDDEN                       | Compressed execution will not be used on some columns, because the average run counts are not large enough.
 SEQUENCE CACHE REFILLED              | Session Cache for a sequence has been used up. Taking a GLOBAL CATALOG X Lock to replenish the cache.
 SIP_FALLBACK                         | Sideways information passing filter disabled due to ineffectiveness.
 SMALL_MERGE_REPLACED                 | Small StorageMerge replaced with StorageUnion for efficiency
 TRANSITIVE PREDICATE                 | The optimizer created a transitive predicate due to a join condition
 WOS_SPILL                            | WOS Full; spilling to a new ROS container
(17 rows)
Have a GREAT day!

NorbertKrupa
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Re: What is the full meaning of the event in query_events?

Post by NorbertKrupa » Fri Apr 11, 2014 2:13 pm

The documentation is mostly non-existent on these query events. My guess is Vertica felt that the description and details for the event were sufficient. However, not all these query events are bad. Some are informational and others (PARTITIONS_ELIMINATED) are good.

I found the following from a Google search:
  • DELETE WITH NON OPTIMIZED PROJECTION - 0
  • GROUPBY PUSHDOWN - 0
  • GROUP_BY_PREPASS_FALLBACK - 1
  • GROUP_BY_SPILLED - 1
  • MEMORY LIMIT HIT - 1
  • MERGE_CONVERTED_TO_UNION - 0
  • NO GROUPBY PUSHDOWN - 0
  • NO HISTOGRAM - 1
  • PARTITIONS_ELIMINATED - 1
  • PREDICATE OUTSIDE HISTOGRAM - 1
  • RESEGMENTED_MANY_ROWS - 0
  • RLE_OVERRIDDEN - 0
  • SEQUENCE CACHE REFILLED - 0
  • SIP_FALLBACK - 1
  • SMALL_MERGE_REPLACED - 0
  • TRANSITIVE PREDICATE - 0
  • WOS_SPILL - 1
Checkout vertica.tips for more Vertica resources.

cbennett
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Re: What is the full meaning of the event in query_events?

Post by cbennett » Sat Apr 12, 2014 6:49 pm

As Norbertk mentioned, most of them are benign and informational.

Things to avoid: SPILL events, MEMORY LIMIT events.

Things to watch out for:

HISTOGRAM events - the workload analyzer output will inform you in the Tuning Recommendations window of the Management Console which projections need to have statistics updated. You can get that information from here, as well.

RESEGMENT and BROADCAST events. They aren't always avoidable, but if you're looking to improve performance, eliminating those will go a long way towards that goal.

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