RE: Partitioned index question

Tim,
Thank you for your reply. This is a LOCAL non-prefixed index. The table is list-partitioned on "APPLICATION_ID" whereas the index is created on ("ACCOUNTING_DATE", "LEDGER_ID", "GL_TRANSFER_STATUS_CODE").

Thanks,
Amir

From: Tim Gorman [mailto:tim.evdbt_at_gmail.com] Sent: Friday, November 18, 2016 12:14 AM To: Hameed, Amir <Amir.Hameed_at_xerox.com>; oracle-l_at_freelists.org Subject: Re: Partitioned index question

Amir,

There are two types of LOCAL partitioned indexes: PREFIXED and NONPREFIXED. PREFIXED indexes have the partition-key column(s) leading the list of concatenated columns on the index. NONPREFIXED indexes have a column other than the partition-key column(s) leading the list.

Queries on PREFIXED indexes always prune perfectly, while queries on NONPREFIXED might span any and every partition in the index.

Think of a very extreme example, a two-column NONPREFIXED index where the leading column has only one data value. Consider a query that filters only only that first column, and for some reason the CBO allows it to perform a indexed FULL SCAN (instead of a FULL table scan). Such an execution plan would require that every partition in the index be materialized with a segment.

Remember: an index is an ordered hierarchical structure, not a "heap" structure like a table. The rules are bound to be different for indexes than for tables.

This is all just a guess: you can prove or disprove it.

Could you check to whether that index is PREFIXED or NONPREFIXED, and then whether *all* partitions in that index have segments?

If the index is NONPREFIXED and all partitions have segments, then it would bear out this guess. Or at least not disprove it, as there might be another reason why all partitions have segments.

If the index is PREFIXED or if any partitions have no corresponding segment, then this guess is likely disproved. Maybe, maybe not, because it is also possible that these segments don't materialize until something accesses them.

Please let us know what you find?

Thanks!

-Tim

On 11/17/16 19:36, Hameed, Amir wrote:
Hi,
While investigating a performance problem, I came across something that didn't make much sense to me and I wanted to see if I am hitting a bug or my concept is not clear. The RDBMS version is 11.2.0.4 and it is an Oracle E-Business Suite database.

The following is an entry from the AWR taken during the time when the AWR showed gc buffer busy acquire waits. Top 10 Foreground Events by Total Wait Time Event

Waits

Total Wait Time (sec)

Wait Avg(ms)

% DB time

Wait Class

db file sequential read

6,074,412

17.6K

3

28.4

User I/O

DB CPU 15.5K

24.9

gc buffer busy acquire

4,086,094

15.1K

4

24.4

Cluster

gc cr block busy

2,102,205

8634.9

4

13.9

Cluster

direct path read

130,665

1375.9

11

2.2

User I/O

Disk file operations I/O

157,121

1212.6

8

2.0

User I/O

db file parallel read

70,297

571.3

8

.9

User I/O

log file sync

53,280

488.6

9

.8

Commit

gc cr disk read

1,615,316

325.4

0

.5

Cluster

utl_file I/O

1,945,047

278.5

0

.4

User I/O

Segments by Global Cache Buffer Busy

• % of Capture shows % of GC Buffer Busy for each top segment compared
• with GC Buffer Busy for all segments captured by the Snapshot Owner

Tablespace Name

Object Name

Subobject Name

Obj. Type

GC Buffer Busy

% of Capture

XLA APPS_TS_TX_IDX XLA_AE_HEADERS_N5 GMF INDEX PARTITION 4,012,420

94.77

XLA APPS_TS_TX_DATA XLA_AE_HEADERS CST TABLE PARTITION 82,466

1.95

APPLSYS APPS_TS_TX_DATA FND_CONCURRENT_REQUESTS TABLE 38,117

0.90

APPLSYS APPS_TS_TX_IDX WF_NOTIFICATIONS_PK INDEX 19,776

0.47

APPLSYS APPS_TS_TX_IDX FND_CONCURRENT_REQUESTS_N9 INDEX 9,940

0.23

Most of the Global Cache Buffer Busy waits are coming from index XLA_AE_HEADERS_N5, partition GMF and this is where it got interesting for me. The DBA_SEGMENTS view shows that there was no segment associated with the GMF partition of table XLA_AE_HEADERS, which is what XLA_AE_HEADERS_N5 is created on. It was also confirmed by the query on DBA_TAB_PARTITIONS:

SQL> select table_name, partition_name, segment_created from dba_tab_partitions where table_name='XLA_AE_HEADERS' and partition_name='GMF' ;

TABLE_NAME                     PARTITION_NAME                 SEGM
------------------------------ ------------------------------ ----
XLA_AE_HEADERS                 GMF                            NO

However, the query against DBA_IND_PARTITION shows that XLA_AE_HEADERS_N5 partition has a segment associated with it: SQL> select index_name, partition_name, segment_created from dba_ind_partitions where index_name='XLA_AE_HEADERS_N5' and partition_name='GMF' ;

INDEX_NAME                     PARTITION_NAME                 SEG
------------------------------ ------------------------------ ---
XLA_AE_HEADERS_N5              GMF                            YES

SQL> select segment_name, partition_name, bytes from dba_segments where segment_name='XLA_AE_HEADERS_N5' and partition_name='GMF';

SEGMENT_NAME                   PARTITION_NAME                           BYTES
------------------------------ ------------------------------ ---------------
XLA_AE_HEADERS_N5              GMF                              2,566,914,048

The index is LOCAL. So, the question is, is it possible for a LOCAL partitioned index to have a segment when the table partition that it is created on does not have a segment associated with it?

Thanks,
Amir

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