SQL> create table t as select 1 id,object_name from dba_objects; Table created. SQL> insert into t select 2,object_name from dba_objects; 50366 rows created. SQL> insert into t select 3,object_name from dba_objects; 50366 rows created. SQL> insert into t select 4,object_name from dba_objects; 50366 rows created. SQL> commit; Commit complete. SQL> create index t_ind on t(id,object_name); Index created. SQL> exec dbms_stats.gather_table_stats('HR','T',cascade=>true); PL/SQL procedure successfully completed. 执行全表扫描 SQL> select /*+ full(t) */ * from t where object_name='EMPLOYEES'; 6 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 1601196873 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 5 | 135 | 215 (3)| 00:00:03 | |* 1 | TABLE ACCESS FULL| T | 5 | 135 | 215 (3)| 00:00:03 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("OBJECT_NAME"='EMPLOYEES') Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 942 consistent gets 0 physical reads 0 redo size 538 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 6 rows processed 不采用hint SQL> select * from t where object_name='EMPLOYEES'; 6 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 2869677071 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 5 | 135 | 5 (0)| 00:00:01 | |* 1 | INDEX SKIP SCAN | T_IND | 5 | 135 | 5 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("OBJECT_NAME"='EMPLOYEES') filter("OBJECT_NAME"='EMPLOYEES') Statistics ---------------------------------------------------------- 1 recursive calls 0 db block gets 17 consistent gets 1 physical reads 0 redo size 538 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 6 rows processed 当全表扫描扫描了942个块Q联合烦引只扫描?7个数据块。可以看到联合烦引的W一个字D늚值重复率很高Ӟ即谓词中没有联合烦引的W一个字D,依然会用index_ss方式Q效率远q高于全表扫描效率。但?/font>W一个字D늚值重复率很低Ӟ使用index_ss的效率要低于全表扫描Q读者可以自行实?/font> 和表的关联相关的hint
/*+ leading(table_1,table_2) */
在多表关联查询中Q指定哪个表作ؓ驱动表,卛_诉优化器首先要访问哪个表上的数据?/span> select /*+ leading(t,t1) */ t.* from t,t1 where t.id=t1.id; /*+ order */
让OracleҎfrom后面表的序来选择驱动表,oracle使用leadingQ他更ؓ灉| select /*+ order */ t.* from t,t1 where t.id=t1.id; /*+ use_nl(table_1,table_2) */ 在多表关联查询中Q指定用nest loops方式q行多表兌?/span>
select /*+ use_nl(t,t1) */ t.* from t,t1 where t.id=t1.id;
select /*+ full(employees) cache(employees) */ last_name from employees 附录hint表格
Hints for Optimization Approaches and Goals
ALL_ROWS
The ALL_ROWS hint explicitly chooses the cost-based approach to optimize a statement block with a goal of best throughput (that is, minimum total resource consumption).
FIRST_ROWS
The FIRST_ROWS hint explicitly chooses the cost-based approach to optimize a statement block with a goal of best response time (minimum resource usage to return first row). In newer Oracle version you should give a parameter with this hint: FIRST_ROWS(n) means that the optimizer will determine an executionplan to give a fast response for returning the first n rows.
CHOOSE
The CHOOSE hint causes the optimizer to choose between the rule-based approach and the cost-based approach for a SQL statement based on the presence of statistics for the tables accessed by the statement
RULE
The RULE hint explicitly chooses rule-based optimization for a statement block. This hint also causes the optimizer to ignore any other hints specified for the statement block. The RULE hint does not work any more in Oracle 10g.
Hints for Access Paths
FULL
The FULL hint explicitly chooses a full table scan for the specified table. The syntax of the FULL hint is FULL(table) where table specifies the alias of the table (or table name if alias does not exist) on which the full table scan is to be performed.
ROWID
The ROWID hint explicitly chooses a table scan by ROWID for the specified table. The syntax of the ROWID hint is ROWID(table) where table specifies the name or alias of the table on which the table access by ROWID is to be performed. (This hint depricated in Oracle 10g)
CLUSTER
The CLUSTER hint explicitly chooses a cluster scan to access the specified table. The syntax of the CLUSTER hint is CLUSTER(table) where table specifies the name or alias of the table to be accessed by a cluster scan.
HASH
The HASH hint explicitly chooses a hash scan to access the specified table. The syntax of the HASH hint is HASH(table) where table specifies the name or alias of the table to be accessed by a hash scan.
HASH_AJ
The HASH_AJ hint transforms a NOT IN subquery into a hash anti-join to access the specified table. The syntax of the HASH_AJ hint is HASH_AJ(table) where table specifies the name or alias of the table to be accessed.(depricated in Oracle 10g)
INDEX
The INDEX hint explicitly chooses an index scan for the specified table. The syntax of the INDEX hint is INDEX(table index) where:table specifies the name or alias of the table associated with the index to be scanned and index specifies an index on which an index scan is to be performed. This hint may optionally specify one or more indexes:
NO_INDEX
The NO_INDEX hint explicitly disallows a set of indexes for the specified table. The syntax of the NO_INDEX hint is NO_INDEX(table index)
INDEX_ASC
The INDEX_ASC hint explicitly chooses an index scan for the specified table. If the statement uses an index range scan, Oracle scans the index entries in ascending order of their indexed values.
INDEX_COMBINE
If no indexes are given as arguments for the INDEX_COMBINE hint, the optimizer will use on the table whatever boolean combination of bitmap indexes has the best cost estimate. If certain indexes are given as arguments, the optimizer will try to use some boolean combination of those particular bitmap indexes. The syntax of INDEX_COMBINE is INDEX_COMBINE(table index).
INDEX_JOIN
Explicitly instructs the optimizer to use an index join as an access path. For the hint to have a positive effect, a sufficiently small number of indexes must exist that contain all the columns required to resolve the query.
INDEX_DESC
The INDEX_DESC hint explicitly chooses an index scan for the specified table. If the statement uses an index range scan, Oracle scans the index entries in descending order of their indexed values.
INDEX_FFS
This hint causes a fast full index scan to be performed rather than a full table.
NO_INDEX_FFS
Do not use fast full index scan (from Oracle 10g)
INDEX_SS
Exclude range scan from query plan (from Oracle 10g)
INDEX_SS_ASC
Exclude range scan from query plan (from Oracle 10g)
INDEX_SS_DESC
Exclude range scan from query plan (from Oracle 10g)
NO_INDEX_SS
The NO_INDEX_SS hint causes the optimizer to exclude a skip scan of the specified indexes on the specified table. (from Oracle 10g)
Hints for Query Transformations
NO_QUERY_TRANSFORMATION
Prevents the optimizer performing query transformations. (from Oracle 10g)
USE_CONCAT
The USE_CONCAT hint forces combined OR conditions in the WHERE clause of a query to be transformed into a compound query using the UNION ALL set operator. Normally, this transformation occurs only if the cost of the query using the concatenations is cheaper than the cost without them.
NO_EXPAND
The NO_EXPAND hint prevents the optimizer from considering OR-expansion for queries having OR conditions or IN-lists in the WHERE clause. Usually, the optimizer considers using OR expansion and uses this method if it decides that the cost is lower than not using it.
REWRITE
The REWRITE hint forces the optimizer to rewrite a query in terms of materialized views, when possible, without cost consideration. Use the REWRITE hint with or without a view list. If you use REWRITE with a view list and the list contains an eligible materialized view, then Oracle uses that view regardless of its cost.
NOREWRITE / NO_REWRITE
In Oracle 10g renamed to NO_REWRITE. The NOREWRITE/NO_REWRITE hint disables query rewrite for the query block, overriding the setting of the parameter QUERY_REWRITE_ENABLED.
MERGE
The MERGE hint lets you merge views in a query.
NO_MERGE
The NO_MERGE hint causes Oracle not to merge mergeable views. This hint is most often used to reduce the number of possible permutations for a query and make optimization faster.
FACT
The FACT hint indicated that the table should be considered as a fact table. This is used in the context of the star transformation.
NO_FACT
The NO_FACT hint is used in the context of the star transformation to indicate to the transformation that the hinted table should not be considered as a fact table.
STAR_TRANSFORMATION
The STAR_TRANSFORMATION hint makes the optimizer use the best plan in which the transformation has been used. Without the hint, the optimizer could make a query optimization decision to use the best plan generated without the transformation, instead of the best plan for the transformed query.
NO_STAR_TRANSFORMATION
Do not use star transformation (from Oracle 10g)
UNNEST
The UNNEST hint specifies subquery unnesting.
NO_UNNEST
Use of the NO_UNNEST hint turns off unnesting for specific subquery blocks.
Hints for Join Orders
LEADING
Give this hint to indicate the leading table in a join. This will indicate only 1 table. If you want to specify the whole order of tables, you can use the ORDERED hint. Syntax: LEADING(table)
ORDERED
The ORDERED hint causes Oracle to join tables in the order in which they appear in the FROM clause. If you omit the ORDERED hint from a SQL statement performing a join , the optimizer chooses the order in which to join the tables. You may want to use the ORDERED hint to specify a join order if you know something about the number of rows selected from each table that the optimizer does not. Such information would allow you to choose an inner and outer table better than the optimizer could.
Hints for Join Operations
USE_NL
The USE_NL hint causes Oracle to join each specified table to another row source with a nested loops join using the specified table as the inner table. The syntax of the USE_NL hint is USE_NL(table table) where table is the name or alias of a table to be used as the inner table of a nested loops join.
NO_USE_NL
Do not use nested loop (from Oracle 10g)
USE_NL_WITH_INDEX
Specifies a nested loops join. (from Oracle 10g)
USE_MERGE
The USE_MERGE hint causes Oracle to join each specified table with another row source with a sort-merge join. The syntax of the USE_MERGE hint is USE_MERGE(table table) where table is a table to be joined to the row source resulting from joining the previous tables in the join order using a sort-merge join.
NO_USE_MERGE
Do not use merge (from Oracle 10g)
USE_HASH
The USE_HASH hint causes Oracle to join each specified table with another row source with a hash join. The syntax of the USE_HASH hint is USE_HASH(table table) where table is a table to be joined to the row source resulting from joining the previous tables in the join order using a hash join.
NO_USE_HASH
Do not use hash (from Oracle 10g)
Hints for Parallel Execution
PARALLEL
The PARALLEL hint allows you to specify the desired number of concurrent query servers that can be used for the query. The syntax is PARALLEL(table number number). The PARALLEL hint must use the table alias if an alias is specified in the query. The PARALLEL hint can then take two values separated by commas after the table name. The first value specifies the degree of parallelism for the given table, the second value specifies how the table is to be split among the instances of a parallel server. Specifying DEFAULT or no value signifies the query coordinator should examine the settings of the initialization parameters (described in a later section) to determine the default degree of parallelism.
NOPARALLEL / NO_PARALLEL
The NOPARALLEL hint allows you to disable parallel scanning of a table, even if the table was created with a PARALLEL clause. In Oracle 10g this hint was renamed to NO_PARALLEL.
PQ_DISTRIBUTE
The PQ_DISTRIBUTE hint improves the performance of parallel join operations. Do this by specifying how rows of joined tables should be distributed among producer and consumer query servers. Using this hint overrides decisions the optimizer would normally make.
NO_PARALLEL_INDEX
The NO_PARALLEL_INDEX hint overrides a PARALLEL attribute setting on an index to avoid a parallel index scan operation.
Additional Hints
APPEND
When the APPEND hint is used with the INSERT statement, data is appended to the table. Existing free space in the block is not used. If a table or an index is specified with nologging, this hint applied with an insert statement produces a direct path insert which reduces generation of redo.
NOAPPEND
Overrides the append mode.
CACHE
The CACHE hint specifies that the blocks retrieved for the table in the hint are placed at the most recently used end of the LRU list in the buffer cache when a full table scan is performed. This option is useful for small lookup tables. In the following example, the CACHE hint overrides the table default caching specification.
NOCACHE
The NOCACHE hint specifies that the blocks retrieved for this table are placed at the least recently used end of the LRU list in the buffer cache when a full table scan is performed. This is the normal behavior of blocks in the buffer cache.
PUSH_PRED
The PUSH_PRED hint forces pushing of a join predicate into the view.
NO_PUSH_PRED
The NO_PUSH_PRED hint prevents pushing of a join predicate into the view.
PUSH_SUBQ
The PUSH_SUBQ hint causes nonmerged subqueries to be evaluated at the earliest possible place in the execution plan.
NO_PUSH_SUBQ
The NO_PUSH_SUBQ hint causes non-merged subqueries to be evaluated as the last step in the execution plan.
QB_NAME
Specifies a name for a query block. (from Oracle 10g)
CURSOR_SHARING_EXACT
Oracle can replace literals in SQL statements with bind variables, if it is safe to do so. This is controlled with the CURSOR_SHARING startup parameter. The CURSOR_SHARING_EXACT hint causes this behavior to be switched off. In other words, Oracle executes the SQL statement without any attempt to replace literals by bind variables.
DRIVING_SITE
The DRIVING_SITE hint forces query execution to be done for the table at a different site than that selected by Oracle
DYNAMIC_SAMPLING
The DYNAMIC_SAMPLING hint lets you control dynamic sampling to improve server performance by determining more accurate predicate selectivity and statistics for tables and indexes. You can set the value of DYNAMIC_SAMPLING to a value from 0 to 10. The higher the level, the more effort the compiler puts into dynamic sampling and the more broadly it is applied. Sampling defaults to cursor level unless you specify a table.
SPREAD_MIN_ANALYSIS
This hint omits some of the compile time optimizations of the rules, mainly detailed dependency graph analysis, on spreadsheets. Some optimizations such as creating filters to selectively populate spreadsheet access structures and limited rule pruning are still used. (from Oracle 10g)
Hints with unknown status
MERGE_AJ
The MERGE_AJ hint transforms a NOT IN subquery into a merge anti-join to access the specified table. The syntax of the MERGE_AJ hint is MERGE_AJ(table) where table specifies the name or alias of the table to be accessed.(depricated in Oracle 10g)
AND_EQUAL
The AND_EQUAL hint explicitly chooses an execution plan that uses an access path that merges the scans on several single-column indexes. The syntax of the AND_EQUAL hint is AND_EQUAL(table index index) where table specifies the name or alias of the table associated with the indexes to be merged. and index specifies an index on which an index scan is to be performed. You must specify at least two indexes. You cannot specify more than five. (depricated in Oracle 10g)
STAR
The STAR hint forces the large table to be joined last using a nested loops join on the index. The optimizer will consider different permutations of the small tables. (depricated in Oracle 10g)
BITMAP
Usage: BITMAP(table_name index_name) Uses a bitmap index to access the table. (depricated ?)
HASH_SJ
Use a Hash Anti-Join to evaluate a NOT IN sub-query. Use this hint in the sub-query, not in the main query. Use this when your high volume NOT IN sub-query is using a FILTER or NESTED LOOPS join. Try MERGE_AJ if HASH_AJ refuses to work.(depricated in Oracle 10g)
NL_SJ
Use a Nested Loop in a sub-query. (depricated in Oracle 10g)
NL_AJ
Use an anti-join in a sub-query. (depricated in Oracle 10g)
SQL> select object_id,session_id from v$locked_object; //注意session_id 是上锁?session标志 SQL> select username,sid,SERIAL# from v$session where sid=。? //q里的SID = session_id SQL> alter system kill session 'id,serial#'; //杀死该session
现在 IT 开发h员比以往M时候都更加x试的重要性,没有l过良好试的代码更Ҏ出问题。在极限~程中,试驱动开发已l被证明是一U有效提高Y件质量的Ҏ。在试驱动的开发方式中QY件工E师在编写功能代码之前首先编写测试代码,q样能从最开始保证程序代码的正确性,q且能够在程序的每次演进时进行自动的回归试。测试对于Y件品的成|L臛_重要的作用,在极限编E领域,甚至有h提议M未经试的代码都应该自动从发布的产品中删除。作者ƈ不确信这个观Ҏ正确的,但是试本n的质量确实是一个需要高度关注的问题。测试的覆盖率是试质量的一个重要指标,我们需要工h帮助我们q行对Y件测试覆盖的考察?/p>
EclEmma 是q样一个能帮助开发h员考察试覆盖率的优秀?Eclipse 开源插件。EclEmma 在覆盖测试领域是如此的优UQ以致于它在q去不久?2006 q成Z Eclipse Community Awards Winners 册选手。虽然最?Eclipse Checkstyle Plugin 取得?Best Open Source Eclipse-based Developer tool 的称P但我们也可以由此看到 EclEmma 对开发h员的帮助是巨大的QEclipse Community Award 的具体信息可以参?参考资?/a>Q?/p>
预插入模式:对程序进行测量之前,需要采?Emma 提供的工具对 class 文g或?jar 文gq行修改。修改完成之后的代码可以立刻被执行。覆盖测试的l果会被存攑ֈ指定的文件中?/li>
x插入模式Q?/strong>x插入模式不需要事先对代码q行修改。相反,对代码的修改是通过一?Emma 定制?Class loaderQ类载入器)q行的。这U方式的优点很明显,我们不需要对 class 或?jar 文gq行M修改。缺Ҏ我们Z获得试的结果,需要用 Emma 提供的命?emmarun 来执?Java 应用E序?/li>
Exception in thread "main" org.codehaus.xfire.XFireRuntimeException: Could not invoke service.. Nested exception is org.codehaus.xfire.fault.XFireFault: 非法的用户名和密?br />org.codehaus.xfire.fault.XFireFault: 非法的用户名和密?br /> at org.codehaus.xfire.fault.Soap11FaultSerializer.readMessage(Soap11FaultSerializer.java:31) at org.codehaus.xfire.fault.SoapFaultSerializer.readMessage(SoapFaultSerializer.java:28) at org.codehaus.xfire.soap.handler.ReadHeadersHandler.checkForFault(ReadHeadersHandler.java:111) at org.codehaus.xfire.soap.handler.ReadHeadersHandler.invoke(ReadHeadersHandler.java:67) at org.codehaus.xfire.handler.HandlerPipeline.invoke(HandlerPipeline.java:131) at org.codehaus.xfire.client.Client.onReceive(Client.java:406) at org.codehaus.xfire.transport.http.HttpChannel.sendViaClient(HttpChannel.java:139) at org.codehaus.xfire.transport.http.HttpChannel.send(HttpChannel.java:48) at org.codehaus.xfire.handler.OutMessageSender.invoke(OutMessageSender.java:26) at org.codehaus.xfire.handler.HandlerPipeline.invoke(HandlerPipeline.java:131) at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:79) at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:114) at org.codehaus.xfire.client.Client.invoke(Client.java:336) at org.codehaus.xfire.client.XFireProxy.handleRequest(XFireProxy.java:77) at org.codehaus.xfire.client.XFireProxy.invoke(XFireProxy.java:57) at $Proxy0.getUser(Unknown Source) at test.ClientTest.main(ClientTest.java:39)
Exception in thread "main" org.codehaus.xfire.XFireRuntimeException: Could not invoke service.. Nested exception is org.codehaus.xfire.fault.XFireFault: h必须包含验证信息 org.codehaus.xfire.fault.XFireFault: h必须包含验证信息 at org.codehaus.xfire.fault.Soap11FaultSerializer.readMessage(Soap11FaultSerializer.java:31) at org.codehaus.xfire.fault.SoapFaultSerializer.readMessage(SoapFaultSerializer.java:28) at org.codehaus.xfire.soap.handler.ReadHeadersHandler.checkForFault(ReadHeadersHandler.java:111) at org.codehaus.xfire.soap.handler.ReadHeadersHandler.invoke(ReadHeadersHandler.java:67) at org.codehaus.xfire.handler.HandlerPipeline.invoke(HandlerPipeline.java:131) at org.codehaus.xfire.client.Client.onReceive(Client.java:406) at org.codehaus.xfire.transport.http.HttpChannel.sendViaClient(HttpChannel.java:139) at org.codehaus.xfire.transport.http.HttpChannel.send(HttpChannel.java:48) at org.codehaus.xfire.handler.OutMessageSender.invoke(OutMessageSender.java:26) at org.codehaus.xfire.handler.HandlerPipeline.invoke(HandlerPipeline.java:131) at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:79) at org.codehaus.xfire.client.Invocation.invoke(Invocation.java:114) at org.codehaus.xfire.client.Client.invoke(Client.java:336) at org.codehaus.xfire.client.XFireProxy.handleRequest(XFireProxy.java:77) at org.codehaus.xfire.client.XFireProxy.invoke(XFireProxy.java:57) at $Proxy0.getUser(Unknown Source) at test.ClientTest.main(ClientTest.java:35)