Autotrace中的Consistent Gets与SQL Trace中的Consistent Read有什么区别？
在Oracle演示HR模式上运行SQL并运行Autotrace和SQL Trace（底部）。我预计块读取的数量将是相同的，但是Autotrace Consistent Gets是21并且SQL Trace Consistent Read是15.我想知道是什么造成了差异。
表没有更新，跟踪表示没有缓存未命中，因此我认为SQL所需的块都在缓存中。
来自USER_INDEXES的表数据块对于EMPLOYESS和DEPARTMENTS都是5。行分别为107和27。
SELECT /*+USE_HASH(e d) */ e.employee_id, e.first_name||' '||e.last_name as full_name, d.department_name
FROM
employees e, departments d
WHERE
e.department_id=d.department_id;
Windows x64上的Oracle 11G R2 人力资源演示架构。
Execution Plan
----------------------------------------------------------
Plan hash value: 2052257371
----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 106 | 4028 | 7 (15)| 00:00:01 |
|* 1 | HASH JOIN | | 106 | 4028 | 7 (15)| 00:00:01 |
| 2 | TABLE ACCESS FULL| DEPARTMENTS | 27 | 432 | 3 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL| EMPLOYEES | 107 | 2354 | 3 (0)| 00:00:01 |
----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
21 consistent gets
0 physical reads
0 redo size
4502 bytes sent via SQL*Net to client
601 bytes received via SQL*Net from client
9 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
106 rows processed
1 SELECT /*+USE_HASH(e d) */ e.employee_id, e.first_name||' '||e.last_name as full_name, d.department_name
2 FROM
3 employees e, departments d
4 WHERE
5 e.department_id=d.department_id
6 -- AND d.department_name = 'IT'
7*
SELECT /*+USE_HASH(e d) */ e.employee_id, e.first_name||' '||e.last_name as full_name, d.department_name
FROM
employees e, departments d
WHERE
e.department_id=d.department_id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 15 0 106
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 0.00 0.00 0 15 0 106
Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 85
Rows Row Source Operation
------- ---------------------------------------------------
106 HASH JOIN (cr=15 pr=0 pw=0 time=105 us cost=7 size=4028 card=106)
27 TABLE ACCESS FULL DEPARTMENTS (cr=7 pr=0 pw=0 time=26 us cost=3 size=432 card=27)
107 TABLE ACCESS FULL EMPLOYEES (cr=8 pr=0 pw=0 time=106 us cost=3 size=2354 card=107)
整个TKPROF输出 TKPROF：版本11.2.0.1.0 - 2014年11月22日星期六20:05:34发展
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
Trace file: nr_ora_6352_HR.trc
Sort options: default
********************************************************************************
count = number of times OCI procedure was executed
cpu = cpu time in seconds executing
elapsed = elapsed time in seconds executing
disk = number of physical reads of buffers from disk
query = number of buffers gotten for consistent read
current = number of buffers gotten in current mode (usually for update)
rows = number of rows processed by the fetch or execute call
********************************************************************************
SQL ID: 909v6n80saka9
Plan Hash: 0
ALTER SESSION SET SQL_TRACE=true
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 0 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 1 0.00 0.00 0 0 0 0
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: 85
********************************************************************************
SELECT /*+USE_HASH(e d) */ e.employee_id, e.first_name||' '||e.last_name as full_name, d.department_name
FROM
employees e, departments d
WHERE
e.department_id=d.department_id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 15 0 106
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 0.00 0.00 0 15 0 106
Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 85
Rows Row Source Operation
------- ---------------------------------------------------
106 HASH JOIN (cr=15 pr=0 pw=0 time=105 us cost=7 size=4028 card=106)
27 TABLE ACCESS FULL DEPARTMENTS (cr=7 pr=0 pw=0 time=26 us cost=3 size=432 card=27)
107 TABLE ACCESS FULL EMPLOYEES (cr=8 pr=0 pw=0 time=106 us cost=3 size=2354 card=107)
********************************************************************************
SQL ID: at7597y1bruv1
Plan Hash: 0
ALTER SESSION SET SQL_TRACE=false
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 2 0.00 0.00 0 0 0 0
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 85
********************************************************************************
OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 2 0.00 0.00 0 0 0 0
Execute 3 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 15 0 106
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 7 0.00 0.00 0 15 0 106
Misses in library cache during parse: 1
Misses in library cache during execute: 1
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 0 0.00 0.00 0 0 0 0
Execute 0 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 0 0.00 0.00 0 0 0 0
Misses in library cache during parse: 0
3 user SQL statements in session.
0 internal SQL statements in session.
3 SQL statements in session.
********************************************************************************
Trace file: nr_ora_6352_HR.trc
Trace file compatibility: 11.1.0.7
Sort options: default
1 session in tracefile.
3 user SQL statements in trace file.
0 internal SQL statements in trace file.
3 SQL statements in trace file.
3 unique SQL statements in trace file.
48 lines in trace file.
0 elapsed seconds in trace file.
之前的Autotrace是从SQL Plus Release 11.2.0.1.0执行的，而SQL Trace是从SQL Developer 4.0.1.14执行的。通过从相同的SQL Plus运行SQL跟踪，结果匹配...
TKPROF: Release 11.2.0.1.0 - Development on Sun Nov 23 11:22:13 2014
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
Trace file: nr_ora_2836_HR.trc
Sort options: default
********************************************************************************
count = number of times OCI procedure was executed
cpu = cpu time in seconds executing
elapsed = elapsed time in seconds executing
disk = number of physical reads of buffers from disk
query = number of buffers gotten for consistent read
current = number of buffers gotten in current mode (usually for update)
rows = number of rows processed by the fetch or execute call
********************************************************************************
SQL ID: 909v6n80saka9
Plan Hash: 0
ALTER SESSION SET SQL_TRACE=true
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 0 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 1 0.00 0.00 0 0 0 0
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: 85
********************************************************************************
SELECT /*+USE_HASH(e d) */ e.employee_id, e.first_name||' '||e.last_name as full_name, d.department_name
FROM
employees e, departments d
WHERE
e.department_id=d.department_id
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 9 0.00 0.00 0 21 0 106
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 11 0.00 0.00 0 21 0 106
Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 85
Rows Row Source Operation
------- ---------------------------------------------------
106 HASH JOIN (cr=21 pr=0 pw=0 time=0 us cost=7 size=4028 card=106)
27 TABLE ACCESS FULL DEPARTMENTS (cr=7 pr=0 pw=0 time=26 us cost=3 size=432 card=27)
107 TABLE ACCESS FULL EMPLOYEES (cr=14 pr=0 pw=0 time=0 us cost=3 size=2354 card=107)
********************************************************************************
SQL ID: at7597y1bruv1
Plan Hash: 0
ALTER SESSION SET SQL_TRACE=false
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 2 0.00 0.00 0 0 0 0
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 85
********************************************************************************
OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 2 0.00 0.00 0 0 0 0
Execute 3 0.00 0.00 0 0 0 0
Fetch 9 0.00 0.00 0 21 0 106
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 14 0.00 0.00 0 21 0 106
Misses in library cache during parse: 1
Misses in library cache during execute: 1
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 0 0.00 0.00 0 0 0 0
Execute 0 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 0 0.00 0.00 0 0 0 0
Misses in library cache during parse: 0
3 user SQL statements in session.
0 internal SQL statements in session.
3 SQL statements in session.
********************************************************************************
Trace file: nr_ora_2836_HR.trc
Trace file compatibility: 11.1.0.7
Sort options: default
1 session in tracefile.
3 user SQL statements in trace file.
0 internal SQL statements in trace file.
3 SQL statements in trace file.
3 unique SQL statements in trace file.
55 lines in trace file.
0 elapsed seconds in trace file.
答案 0 :(得分：3)
不同之处在于tkprof输出显示了您的单个SELECT语句，但是autotrace输出的Statistics部分总结了2个语句，SELECT和1个递归调用，如该部分的第一行所示。
递归调用的一些示例是：触发器（INSERT，UPDATE，DELETE），动态采样（如果缺少表统计信息）或内部语句在第一次执行时查询数据字典中的数据。
尝试使用autotrace至少运行两次语句，并检查连续执行时此1次递归调用是否仍然存在。如果是，则SQL跟踪应包含SELECT语句和递归SQL。您应该将它们的总和与autotrace输出进行比较。 Tkprof报告跟踪文件中找到的SQL语句的递归级别以及总摘要。