PureScale不支持的特性, 表與表空間設計的考慮.

TABLESPACE:

Only automatic storage table spaces can be created in a DB2 pureScale environment.

In a DB2 pureScale environment, you should use an extent size of at least 32 pages. This minimum extent size reduces the amount of internal message traffic within the DB2 pureScale environment when extents are added for a table or index.

Small pagesize helps to alleviate page reclaim.



TABLE:

Multidimensional clustering tables are not supported in a DB2 pureScale environment.

ITC tables are not supported in a DB2 pureScale environment.

Range-clustered tables are not supported in a DB2 pureScale environment.

Increasing PCTFREE helps to alleviate page reclaim.

In a multi-partition or DB2 pureScale environment, use the CACHE and NO ORDER options to allow multiple members to cache sequence values simultaneously.



INDEX:

DB2 Version 10.5 adds a type of random ordering for index key columns. Random ordering on index columns helps to alleviate page contention on frequently accessed pages in certain insert scenarios.

This new function focuses specifically on index leaf pages that are accessed frequently in a DB2 pureScale environment.

If rows are added to a table in the order of an index, the last leaf page of the index is frequently accessed. The last leaf page is frequently accessed since every key added to the index is inserted into the page. This situation is most common when there is an index on a timestamp, or identity column with increasing keys.

This problem is further exacerbated in a DB2 pureScale environment, where pages are shared between multiple members. In a DB2 pureScale environment, rather than just having latch contention on the page, the page itself must go back and forth to the cluster caching facility. The cluster caching facility then moves the page to the different members that are updating or inserting into it. This situation leads to a drastic drop in throughput.

When you specify the RANDOM option, values are stored at random places in the index tree. As a result, the number of consecutive insertions on a page decreases. Which in turn, alleviates the issue of page contention. You can use a randomly ordered index to run equality lookups on a specified column. In addition, key columns that are in random order can be used in nonmatching index scans, and index-only access on random key columns is possible. Even though values are stored in random order, you can retrieve the original value of the random key column.



CURRENT COMMIT:

In a DB2 pureScale environment, currently committed semantics only apply to lock conflicts between applications running on the same member. If the lock conflict is with an application on a remote member, the requester of the lock waits for the lock to be released before processing the row.



OTHERS:

Starting with DB2 Cancun Release 10.5.0.4, inplace table reorganization is supported in DB2 pureScale environments.

Starting with DB2 Cancun Release 10.5.0.4, each member in a DB2 pureScale environment has its own self-tuning memory manager (STMM) tuner.

Health monitor is not supported in DB2 pureScale environments.

The DAS is not supported in DB2 pureScale environments.