HYBRID TSM/HWMB in Explain plan

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Ab 12c stellt Oracle im Plan mehr Infos zum internen Space-Management bereit.


--------------------------------------------------------------------------------------------
| Id  | Operation                          | Name     | Rows  |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------------------------
|   0 | INSERT STATEMENT                   |          |    39 |        |      |            |
|   1 |  PX COORDINATOR                    |          |       |        |      |            |
|   2 |   PX SEND QC (RANDOM)              | :TQ10000 |    39 |  Q1,00 | P->S | QC (RAND)  |
|   3 |    LOAD AS SELECT (HYBRID TSM/HWMB)| T1       |       |  Q1,00 | PCWP |            |
|   4 |     OPTIMIZER STATISTICS GATHERING |          |    39 |  Q1,00 | PCWP |            |
|   5 |      PX BLOCK ITERATOR             |          |    39 |  Q1,00 | PCWC |            |
|   6 |       TABLE ACCESS FULL            | T        |    39 |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------------------------

and we said...

Its part of the new mechanisms for space management for direct load in 12c. 


Zusammenfassung des unteren der beiden Dokumente:

High Water Mark (HWM) Loading
default approach if you load data serially into a table


Temp Segment Merge (TSM) Loading
achieve parallel data loading in Oracle and is the default mechanism for parallel loads into single segments in Oracle Database 11g Release 2


High Water Mark Brokering (HWMB)
...used if multiple PX servers can potentially fill the same table or partition segment


Oracle Database 12c:  Hybrid TSM/HWMB
...improve the scalability of parallel direct path load, particularly when it’s used to populate single database segments such as non-partitioned tables or individual table partitions


In Oracle Database 12c:
  • Parallel create table as select, INSERT and MERGE operations use Hybrid TSM/HWMB instead of temp segment merge for single segment loads. It is used in both Auto DOP and manual DOP environments.
  • Temp segment merge continues to be available for some partitioned table parallel create table as select operations because this approach is highly scalable and (since it is a one-time operation) it avoids the potential downsides related to space fragmentation and extent bloat.
  • Hybrid TSM/HWMB is used instead of temp segment merge for some partitioned table parallel create table as select operations.
  • Space management decorations are clearly shown in execution plans for parallel load operations from database version 12.1.0.2. LOAD AS SELECT is decorated with “TEMP SEGMENT MERGE”, “HIGH WATER MARK BROKERED”, “HIGH WATER MARK”, “HYBRID TSM/HWMB” or “EQUI-PARTITION”.

Quellen:
- https://asktom.oracle.com/pls/apex/asktom.search?tag=hybrid-tsmhwmb-in-explain-plan
mit Verweis auf
- https://blogs.oracle.com/optimizer/space-management-and-oracle-direct-path-load

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