Distinct placement

As a follow-up to a recent post on different names Oracle can use for the intermediate views, here is a quick example of the technique called distinct placement.

Automatic shared memory resize with disabled ASMM/AMM

Thanks to Nigel Antell – he has posted a comment on one of Tanel Poder’s blog notes with a link to MOS Doc ID 1269139.1. In this note a parameter called _MEMORY_IMM_MODE_WITHOUT_AUTOSGA is described. It allows Oracle 11gR2 to adjust sizes of shared memory structures even if Automatic (Shared) Memory Management have been explicitly disabled; with the main purpose of avoiding ORA-04031 error. This is nice.
PS. I wonder if it was done by Oracle development specifically due to many customers don’t like ASMM (for ex. because of negative impact on application) but encounter ORA-04031 from time to time, which results in many opened SRs. Who knows.

PQ_DISTRIBUTE enhancement – Part 1

Oracle 11g has introduced a hell lot of new features related to Parallel Execution – like statement queuing, in-memory PX and auto-DOP, to name a few. There are also small bits of enhancements here and there – like default value of the PARALLEL_EXECUTION_MESSAGE_SIZE and an introduction of an easy way to stick PX slaves to a current RAC node with PARALLEL_FORCE_LOCAL. As I’ve recently discovered, PQ_DISTRIBUTE hint used only for joins prior to 11gR2, can now be used for load operations.

_connect_by_use_union_all

This is just a short note on the parameter introduced in the 11gR2 called _connect_by_use_union_all. I’ve noticed it for the first time in Doc ID 7210630.8, which gives a brief overview of the changes made to the way CBO generates plans for hierarchical queries. As usually happens, the change helps to one problem, but produces a bunch of unexpected side effects, such as wrong or incorrect results, and even ORA-00904 in a simple case. All these bugs have been fixed in the 11.2.0.2 patch set, but who knows how many issues related to the change are still there? If you see something unusual with a standard Oracle hierarchical query in the 11gR2, I think it’s good to try turning this parameter off and see if it helps.

DBMS_PARALLEL_EXECUTE

Here is a recent thread from OTN forums. The question raised is WTF? whether a hint in the examples section of DBMS_PARALLEL_EXECUTE documentation have to be used or not and why it is there. What do you think about it? Have a look in the documentation and mark your choice in a poll:

PS. In my view it’s a bug. I left a comment in the documentation about it, but didn’t receive any reply yet.

Missing wait event

Oracle 11.2.0.1 for Windows is out for some time. I’ve installed it on my 32-bit Windows XP machine because I like Windows 🙂 – just to check that it’s actually working fine. Playing with TPC-H test using Hammerora I’ve noticed an anomaly in the way Oracle reports IO waits for some queries.

ORA-01719 is partially relaxed

You most likely have seen this error before:

ORA-01719: outer join operator (+) not allowed in operand of OR or IN
Cause: An outer join appears in an or clause.
Action: If A and B are predicates, to get the effect of (A(+) or B), try (select where (A(+) and not B)) union all (select where (B)).

In 11gR2 it is no longer raised for predicates like column(+) IN (constant1, constant2, …).

Enhanced Subquery Optimizations in Oracle

While googling I found a fresh article from Oracle for the VLDB journal: Enhanced Subquery Optimization in Oracle. It primarily discusses subqueries – how Oracle deals with them on optimization and at run-time.

Cardinality of table collection expression

Table collection expression has been in Oracle for more than 10 years. It is handy for passing an array to Oracle. Quite often, though, there is was a well-known problem with a default cardinality associated with table collection expressions used in the SQL.

Control file sequential read

There was a thread recently on the OTN forum (it’s currently down, that’s why I’m writing in the blog; here is a stale version of the page from Google cache; at the time of writing this version had 1 comment) about reasons for control file sequential read accounted to particular query.

RAC is not a requirement for in-memory PX

As pointed out by Greg Rahn in the comments to Mark Rittman’s blog post, new Oracle 11gR2 feature called In-Memory Parallel Execution work well in a single-instance environment.

COALESCE_SQ

There are 19 new hints in Oracle 11.2.0.1:

SQL> select name from v$sql_hint where version='11.2.0.1';

NAME
------------------------------
COALESCE_SQ
NO_COALESCE_SQ
TRANSFORM_DISTINCT_AGG
NO_TRANSFORM_DISTINCT_AGG
CONNECT_BY_ELIM_DUPS
NO_CONNECT_BY_ELIM_DUPS
DST_UPGRADE_INSERT_CONV
NO_DST_UPGRADE_INSERT_CONV
STATEMENT_QUEUING
NO_STATEMENT_QUEUING
EXPAND_TABLE
NO_EXPAND_TABLE
XMLINDEX_SEL_IDX_TBL
FACTORIZE_JOIN
NO_FACTORIZE_JOIN
APPEND_VALUES
PLACE_DISTINCT
NO_PLACE_DISTINCT
NO_SUBSTRB_PAD

19 rows selected.

Some of them represents new CBO features (like FACTORIZE_JOIN/NO_FACTORIZE_JOIN). Here I’ll show purpose of COALESCE_SQ hint (NO_COALESCE is it’s inverse).

Oracle 11gR2 trace files

Today I’ve run into a deadlock on my test 11gR2 database. The deadlock wasn’t something peculiar, but generated trace file was.

Join factorization

Oracle 11.2.0.1 has introduced one of the most intuitive features to the cost-based transformation: join factorization.