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Oracle SQL多版本VERSION_COUNT产生的可能性

Oracle数据库中执行的SQL,很多时候会因为种种原因产生多个不同的执行版本,一个游标的版本过多很容易引起数据库的性能问题,甚至故障。

有时候一个SQL的版本数量可能多达数万个,以下是我之前在恩墨讲堂分享过的一个案例

07.png

产生SQL多版本的原因很多,通过如下的一些测试我们可以稍微来看看如何分析和找到可能的原因。

以下作为一个基础测试数据,一条基本的SQL查询:


create table t1(c1 int, c2 nvarchar2(100));
alter system flush shared_pool;
var b1 number;
var b2 varchar2(10);
exec :b1 := 1;
exec :b2 := '0';
select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2;


如果我们修改了优化器参数、环境变量、绑定变量等,都可能使得SQL发生重新解析,产生不同的子游标,也就是不同的VERSION。

SQL> set serveroutput on
SQL> set echo on
SQL> drop table t1 purge;

Table dropped.

SQL> create table t1(c1 int, c2 nvarchar2(100));

Table created.

SQL> alter system flush shared_pool;

System altered.

SQL> var b1 number;
SQL> var b2 varchar2(10);
SQL> exec :b1 := 1;

PL/SQL procedure successfully completed.

SQL> exec :b2 := '0';

PL/SQL procedure successfully completed.

SQL> select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2;

no rows selected

Rem 这里我们修改了NLS_SORT参数,再来查看SQL的游标数。
SQL> alter session set nls_sort = 'SCHINESE_RADICAL_M'; Session altered. SQL> select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2; no rows selected SQL> exec shared_cursor('3yr4fwqux2buz') SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 0000000088F64328 CHILD_NUMBER = 0 -------------------------------------------------- SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 0000000087AE2D38 CHILD_NUMBER = 1 LANGUAGE_MISMATCH = Y -------------------------------------------------- REM 注意,以上第一个Child就是因为语言不匹配产生的(LANGUAGE_MISMATCH) REM 以下修改了优化器模式,又一个新的子游标将会因此而产生。
SQL> alter session set optimizer_mode = first_rows; Session altered. SQL> select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2; no rows selected SQL> exec shared_cursor('3yr4fwqux2buz') SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 0000000088F64328 CHILD_NUMBER = 0 -------------------------------------------------- SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 0000000087AE2D38 CHILD_NUMBER = 1 LANGUAGE_MISMATCH = Y -------------------------------------------------- SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 000000008A1B2678 CHILD_NUMBER = 2 OPTIMIZER_MODE_MISMATCH = Y -------------------------------------------------- REM 可以看到,第二个子游标是因为优化器模式不匹配产生的,OPTIMIZER_MODE_MISMATCH.
REM 以下步骤,我们绑定了不同长度的绑定变量,由此又可能产生新的SQL版本。 SQL> var b2 varchar2(2000); SQL> exec :b2 := '0'; PL/SQL procedure successfully completed. SQL> select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2; no rows selected SQL> exec shared_cursor('3yr4fwqux2buz') SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 0000000088F64328 CHILD_NUMBER = 0 -------------------------------------------------- SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 0000000087AE2D38 CHILD_NUMBER = 1 LANGUAGE_MISMATCH = Y -------------------------------------------------- SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 000000008A1B2678 CHILD_NUMBER = 2 OPTIMIZER_MODE_MISMATCH = Y -------------------------------------------------- SQL_TEXT = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2 SQL_ID = 3yr4fwqux2buz ADDRESS = 0000000088361678 CHILD_ADDRESS = 00000000876C6E38 CHILD_NUMBER = 3 BIND_LENGTH_UPGRADEABLE = Y -------------------------------------------------- REM 我们看到的第三个子游标就是因为绑定变量长度不同而产生的。

从Oracle 9i开始,Oracle对中文语言方式(Simplified Chinese和Traditional Chinese)提供了多种排序方式。主要由以下四种,大家可以进行修改尝试:

SCHINESE_RADICAL_M   针对简体中文,按照部首(第一顺序)、笔划(第二顺序)排序
SCHINESE_STROKE_M    针对简体中文,按照笔划(第一顺序)、部首(第二顺序)排序
SCHINESE_PINYIN_M       针对简体中文,按照拼音排序
TCHINESE_RADICAL_M    针对繁体中文,按照部首(第一顺序)、笔划(第二顺序)排序
TCHINESE_STROKE_M     针对繁体中文,按照笔划(第一顺序)、部首(第二顺序)排序

当然可以逐一尝试:

SQL> alter session set nls_sort = 'TCHINESE_RADICAL_M';

Session altered.

SQL> select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2;

no rows selected

SQL> exec shared_cursor('3yr4fwqux2buz')
SQL_TEXT                       = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2
SQL_ID                         = 3yr4fwqux2buz
ADDRESS                        = 0000000088361678
CHILD_ADDRESS                  = 0000000088F64328
CHILD_NUMBER                   = 0
--------------------------------------------------
SQL_TEXT                       = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2
SQL_ID                         = 3yr4fwqux2buz
ADDRESS                        = 0000000088361678
CHILD_ADDRESS                  = 0000000087AE2D38
CHILD_NUMBER                   = 1
LANGUAGE_MISMATCH              = Y
--------------------------------------------------
SQL_TEXT                       = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2
SQL_ID                         = 3yr4fwqux2buz
ADDRESS                        = 0000000088361678
CHILD_ADDRESS                  = 000000008A1B2678
CHILD_NUMBER                   = 2
OPTIMIZER_MODE_MISMATCH        = Y
--------------------------------------------------
SQL_TEXT                       = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2
SQL_ID                         = 3yr4fwqux2buz
ADDRESS                        = 0000000088361678
CHILD_ADDRESS                  = 00000000876C6E38
CHILD_NUMBER                   = 3
BIND_LENGTH_UPGRADEABLE        = Y
--------------------------------------------------
SQL_TEXT                       = select /* test */ * from t1 where c1 = :b1 and c2 = :b2 order by c2
SQL_ID                         = 3yr4fwqux2buz
ADDRESS                        = 0000000088361678
CHILD_ADDRESS                  = 0000000087AD8AB0
CHILD_NUMBER                   = 4
LANGUAGE_MISMATCH              = Y
--------------------------------------------------

以上测试是基于11.2.0.3版本,在Oracle 12c中,相关的可能因素已经多达64个,参考官方手册可以了解 V$SQL_SHARED_CURSOR 的更详细信息。

转引Oracle 12.1的V$SQL_SHARED_CURSOR说明,列举如下,供参考。

V$SQL_SHARED_CURSOR explains why a particular child cursor is not shared with existing child cursors. Each column identifies a specific reason why the cursor cannot be shared.


ColumnDatatypeDescription

SQL_ID

VARCHAR2(13)

SQL identifier

ADDRESS

RAW(4 | 8)

Address of the parent cursor

CHILD_ADDRESS

RAW(4 | 8)

Address of the child cursor

CHILD_NUMBER

NUMBER

Child number

UNBOUND_CURSOR

VARCHAR2(1)

(Y|N) The existing child cursor was not fully built (in other words, it was not optimized)

SQL_TYPE_MISMATCH

VARCHAR2(1)

(Y|N) The SQL type does not match the existing child cursor

OPTIMIZER_MISMATCH

VARCHAR2(1)

(Y|N) The optimizer environment does not match the existing child cursor

OUTLINE_MISMATCH

VARCHAR2(1)

(Y|N) The outlines do not match the existing child cursor

STATS_ROW_MISMATCH

VARCHAR2(1)

(Y|N) The existing statistics do not match the existing child cursor

LITERAL_MISMATCH

VARCHAR2(1)

(Y|N) Non-data literal values do not match the existing child cursor

FORCE_HARD_PARSE

VARCHAR2(1)

(Y|N) For internal use

EXPLAIN_PLAN_CURSOR

VARCHAR2(1)

(Y|N) The child cursor is an explain plan cursor and should not be shared

BUFFERED_DML_MISMATCH

VARCHAR2(1)

(Y|N) Buffered DML does not match the existing child cursor

PDML_ENV_MISMATCH

VARCHAR2(1)

(Y|N) PDML environment does not match the existing child cursor

INST_DRTLD_MISMATCH

VARCHAR2(1)

(Y|N) Insert direct load does not match the existing child cursor

SLAVE_QC_MISMATCH

VARCHAR2(1)

(Y|N) The existing child cursor is a slave cursor and the new one was issued by the coordinator (or, the existing child cursor was issued by the coordinator and the new one is a slave cursor)

TYPECHECK_MISMATCH

VARCHAR2(1)

(Y|N) The existing child cursor is not fully optimized

AUTH_CHECK_MISMATCH

VARCHAR2(1)

(Y|N) Authorization/translation check failed for the existing child cursor

BIND_MISMATCH

VARCHAR2(1)

(Y|N) The bind metadata does not match the existing child cursor

DESCRIBE_MISMATCH

VARCHAR2(1)

(Y|N) The typecheck heap is not present during the describe for the child cursor

LANGUAGE_MISMATCH

VARCHAR2(1)

(Y|N) The language handle does not match the existing child cursor

TRANSLATION_MISMATCH

VARCHAR2(1)

(Y|N) The base objects of the existing child cursor do not match

BIND_EQUIV_FAILURE

VARCHAR2(1)

(Y|N) The bind value's selectivity does not match that used to optimize the existing child cursor

INSUFF_PRIVS

VARCHAR2(1)

(Y|N) Insufficient privileges on objects referenced by the existing child cursor

INSUFF_PRIVS_REM

VARCHAR2(1)

(Y|N) Insufficient privileges on remote objects referenced by the existing child cursor

REMOTE_TRANS_MISMATCH

VARCHAR2(1)

(Y|N) The remote base objects of the existing child cursor do not match

LOGMINER_SESSION_MISMATCH

VARCHAR2(1)

(Y|N) LogMiner Session parameters mismatch

INCOMP_LTRL_MISMATCH

VARCHAR2(1)

(Y|N) Cursor might have some binds (literals) which may be unsafe/non-data. Value mismatch.

OVERLAP_TIME_MISMATCH

VARCHAR2(1)

(Y|N) Mismatch caused by setting session parameter ERROR_ON_OVERLAP_TIME

EDITION_MISMATCH

VARCHAR2(1)

(Y|N) Cursor edition mismatch

MV_QUERY_GEN_MISMATCH

VARCHAR2(1)

(Y|N) Internal, used to force a hard-parse when analyzing materialized view queries

USER_BIND_PEEK_MISMATCH

VARCHAR2(1)

(Y|N) Cursor is not shared because value of one or more user binds is different and this has a potential to change the execution plan

TYPCHK_DEP_MISMATCH

VARCHAR2(1)

(Y|N) Cursor has typecheck dependencies

NO_TRIGGER_MISMATCH

VARCHAR2(1)

(Y|N) Cursor and child have no trigger mismatch

FLASHBACK_CURSOR

VARCHAR2(1)

(Y|N) Cursor non-shareability due to flashback

ANYDATA_TRANSFORMATION

VARCHAR2(1)

(Y|N) Is criteria for opaque type transformation and does not match

PDDL_ENV_MISMATCH

VARCHAR2(1)

(Y|N) Environment setting mismatch for parallel DDL cursor (that is, one or more of the following parameter values have changed: PARALLEL_EXECUTION_ENABLEDPARALLEL_DDL_MODEPARALLEL_DDL_FORCED_DEGREE, orPARALLEL_DDL_FORCED_INSTANCES)

TOP_LEVEL_RPI_CURSOR

VARCHAR2(1)

(Y|N) Is top level RPI cursor

DIFFERENT_LONG_LENGTH

VARCHAR2(1)

(Y|N) Value of LONG does not match

LOGICAL_STANDBY_APPLY

VARCHAR2(1)

(Y|N) Logical standby apply context does not match

DIFF_CALL_DURN

VARCHAR2(1)

(Y|N) If Slave SQL cursor/single call

BIND_UACS_DIFF

VARCHAR2(1)

(Y|N) One cursor has bind UACs and one does not

PLSQL_CMP_SWITCHS_DIFF

VARCHAR2(1)

(Y|N) PL/SQL anonymous block compiled with different PL/SQL compiler switches

CURSOR_PARTS_MISMATCH

VARCHAR2(1)

(Y|N) Cursor was compiled with subexecution (cursor parts were executed)

STB_OBJECT_MISMATCH

VARCHAR2(1)

(Y|N) STB is an internal name for a SQL Management Object Mismatch. A SQL Management Object Mismatch means that either a SQL plan baseline, or a SQL profile, or a SQL patch has been created for your SQL statement between the executions. Because a cursor is a read-only entity, a hard parse is forced to be able to create a new cursor that contains information about the new SQL management object related to this SQL statement.

CROSSEDITION_TRIGGER_MISMATCH

VARCHAR2(1)

(Y|N) The set of crossedition triggers to execute might differ

PQ_SLAVE_MISMATCH

VARCHAR2(1)

(Y|N) Top-level slave decides not to share cursor

TOP_LEVEL_DDL_MISMATCH

VARCHAR2(1)

(Y|N) Is top-level DDL cursor

MULTI_PX_MISMATCH

VARCHAR2(1)

(Y|N) Cursor has multiple parallelizers and is slave-compiled

BIND_PEEKED_PQ_MISMATCH

VARCHAR2(1)

(Y|N) Cursor based around bind peeked values

MV_REWRITE_MISMATCH

VARCHAR2(1)

(Y|N) Cursor needs recompilation because an SCN was used during compile time due to being rewritten by materialized view

ROLL_INVALID_MISMATCH

VARCHAR2(1)

(Y|N) Marked for rolling invalidation and invalidation window exceeded

OPTIMIZER_MODE_MISMATCH

VARCHAR2(1)

(Y|N) Parameter OPTIMIZER_MODE mismatch (for example, all_rows versus first_rows_1)

PX_MISMATCH

VARCHAR2(1)

(Y|N) Mismatch in one parameter affecting the parallelization of a SQL statement. For example, one cursor was compiled with parallel DML enabled while the other was not.

MV_STALEOBJ_MISMATCH

VARCHAR2(1)

(Y|N) Cursor cannot be shared because there is a mismatch in the list of materialized views which were stale when the cursor was built

FLASHBACK_TABLE_MISMATCH

VARCHAR2(1)

(Y|N) Cursor cannot be shared because there is a mismatch with triggers being enabled and/or referential integrity constraints being deferred

LITREP_COMP_MISMATCH

VARCHAR2(1)

(Y|N) Mismatch in use of literal replacement

PLSQL_DEBUG

VARCHAR2(1)

(Y|N) Value of the PLSQL_DEBUG parameter for the current session does not match the value used to build the cursor

LOAD_OPTIMIZER_STATS

VARCHAR2(1)

(Y|N) A hard parse is forced to initialize extended cursor sharing

ACL_MISMATCH

VARCHAR2(1)

(Y|N) Cached ACL evaluation result stored in the child cursor is not valid for the current session or user

FLASHBACK_ARCHIVE_MISMATCH

VARCHAR2(1)

(Y|N) Value of the FLASHBACK_DATA_ARCHIVE_INTERNAL_CURSOR parameter for the current session does not match the value used to build the cursor

LOCK_USER_SCHEMA_FAILED

VARCHAR2(1)

(Y|N) User or schema used to build the cursor no longer exists

Note: This sharing criterion is deprecated

REMOTE_MAPPING_MISMATCH

VARCHAR2(1)

(Y|N) Reloaded cursor was previously remote-mapped and is currently not remote-mapped. Therefore, the cursor must be reparsed.

LOAD_RUNTIME_HEAP_FAILED

VARCHAR2(1)

(Y|N) Loading of run-time heap for the new cursor (or reload of aged out cursor) failed

HASH_MATCH_FAILED

VARCHAR2(1)

(Y|N) No existing child cursors have the unsafe literal bind hash values required by the current cursor

PURGED_CURSOR

VARCHAR2(1)

(Y|N) Child cursor is marked for purging

BIND_LENGTH_UPGRADEABLE

VARCHAR2(1)

(Y|N) Bind length(s) required for the current cursor are longer than the bind length(s) used to build the child cursor

USE_FEEDBACK_STATS

VARCHAR2(1)

(Y|N) A hard parse is forced so that the optimizer can reoptimize the query with improved optimizer inputs (for example, cardinality estimates)

REASON

CLOB

Child number, id, and reason the cursor is not shared. The content of this column is structured using XML.

CON_ID

NUMBER

The ID of the container to which the data pertains. Possible values include:

  • 0: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs.

  • 1: This value is used for rows containing data that pertain to only the root

  • n: Where n is the applicable container ID for the rows containing data


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By eygle on 2015-09-25 13:21 | Comments (0) | HowTo | 3184 |


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