▷ Oracle动态视图v$sql的说明和使用
1.背景
前段时间，利用v$sql分析过一个项目的数据流程。发现对v$sql的一些字段理解的一知半解。 实质是对Oracel的sql执行机制理解不深。 把相关的总结一下。
2.v$sql的定义
ColumnDatatypeDescription SQL_TEXT
VARCHAR2(1000)
First thousand characters of the SQL text for the current cursor
SQL_FULLTEXT
CLOB
All characters of the SQL text for the current cursor
SQL_ID
VARCHAR2(13)
SQL identifier of the parent cursor in the library cache
SHARABLE_MEM
NUMBER
Amount of shared memory used by a cursor. If multiple child cursors exist, then the sum of all shared memory used by all child cursors.
PERSISTENT_MEM
NUMBER
Fixed amount of memory used for the lifetime of an open cursor. If multiple child cursors exist, then the fixed sum of memory used for the lifetime of all the child cursors.
RUNTIME_MEM
NUMBER
Fixed amount of memory required during execution of a cursor. If multiple child cursors exist, then the fixed sum of all memory required during execution of all the child cursors.
SORTS
NUMBER
Sum of the number of sorts that were done for all the child cursors
VERSION_COUNT
NUMBER
Number of child cursors that are present in the cache under this parent
LOADED_VERSIONS
NUMBER
Number of child cursors that are present in the cache and have their context heap loaded
OPEN_VERSIONS
NUMBER
Number of child cursors that are currently open under this current parent
USERS_OPENING
NUMBER
Number of users that have any of the child cursors open
FETCHES
NUMBER
Number of fetches associated with the SQL statement
EXECUTIONS
NUMBER
Total number of executions, totalled over all the child cursors
PX_SERVERS_EXECUTIONS
NUMBER
Total number of executions performed by parallel execution servers (0 when the statement has never been executed in parallel)
END_OF_FETCH_COUNT
NUMBER
Number of times this cursor was fully executed since the cursor was brought into the library cache. The value of this statistic is not incremented when the cursor is partially executed, either because it failed during the execution or because only the first few rows produced by this cursor are fetched before the cursor is closed or re-executed. By definition, the value of the END_OF_FETCH_COUNT column should be less or equal to the value of the EXECUTIONS column.
USERS_EXECUTING
NUMBER
Total number of users executing the statement over all child cursors
LOADS
NUMBER
Number of times the object was loaded or reloaded
FIRST_LOAD_TIME
VARCHAR2(19)
Timestamp of the parent creation time
INVALIDATIONS
NUMBER
Total number of invalidations over all the child cursors
PARSE_CALLS
NUMBER
Sum of all parse calls to all the child cursors under this parent
DISK_READS
NUMBER
Sum of the number of disk reads over all child cursors
DIRECT_WRITES
NUMBER
Sum of the number of direct writes over all child cursors
BUFFER_GETS
NUMBER
Sum of buffer gets over all child cursors
APPLICATION_WAIT_TIME
NUMBER
Application wait time (in microseconds)
CONCURRENCY_WAIT_TIME
NUMBER
Concurrency wait time (in microseconds)
CLUSTER_WAIT_TIME
NUMBER
Cluster wait time (in microseconds)
USER_IO_WAIT_TIME
NUMBER
User I/O Wait Time (in microseconds)
PLSQL_EXEC_TIME
NUMBER
PL/SQL execution time (in microseconds)
JAVA_EXEC_TIME
NUMBER
Java execution time (in microseconds)
ROWS_PROCESSED
NUMBER
Total number of rows processed on behalf of this SQL statement
COMMAND_TYPE
NUMBER
Oracle command type definition
OPTIMIZER_MODE
VARCHAR2(10)
Mode under which the SQL statement was executed
OPTIMIZER_COST
NUMBER
Cost of this query given by the optimizer
OPTIMIZER_ENV
RAW(2000)
Optimizer environment
OPTIMIZER_ENV_HASH_VALUE
NUMBER
Hash value for the optimizer environment
PARSING_USER_ID
NUMBER
User ID of the user that has parsed the very first cursor under this parent
PARSING_SCHEMA_ID
NUMBER
Schema ID that was used to parse this child cursor
PARSING_SCHEMA_NAME
VARCHAR2(30)
Schema name that was used to parse this child cursor
KEPT_VERSIONS
NUMBER
Number of child cursors that have been marked to be kept using the DBMS_SHARED_POOL package
ADDRESS
RAW(4 | 8)
Address of the handle to the parent for this cursor
HASH_VALUE
NUMBER
Hash value of the parent statement in the library cache
OLD_HASH_VALUE
NUMBER
Old SQL hash value
PLAN_HASH_VALUE
NUMBER
Numeric representation of the current SQL plan for this cursor. Comparing one PLAN_HASH_VALUE to another easily identifies whether or not two plans are the same (rather than comparing the two plans line by line).
FULL_PLAN_HASH_VALUE
NUMBER
Numeric representation of the complete SQL plan for this cursor. Comparing one FULL_PLAN_HASH_VALUE to another easily identifies whether or not two plans are the same (rather than comparing the two plans line by line). Note that the FULL_PLAN_HASH_VALUE cannot be compared across databases releases. It is not backward compatible.
MODULE
VARCHAR2(64)
Contains the name of the module that was executing when the SQL statement was first parsed as set by calling DBMS_APPLICATION_INFO.SET_MODULE
MODULE_HASH
NUMBER
Hash value of the module that is named in the MODULE column
ACTION
VARCHAR2(64)
Contains the name of the action that was executing when the SQL statement was first parsed as set by calling DBMS_APPLICATION_INFO.SET_ACTION
ACTION_HASH
NUMBER
Hash value of the action that is named in the ACTION column
SERIALIZABLE_ABORTS
NUMBER
Number of times the transaction failed to serialize, producing ORA-08177 errors, totalled over all the child cursors
OUTLINE_CATEGORY
VARCHAR2(64)
If an outline was applied during construction of the cursor, then this column displays the category of that outline. Otherwise the column is left blank.
CPU_TIME
NUMBER
CPU time (in microseconds) used by this cursor for parsing, executing, and fetching
ELAPSED_TIME
NUMBER
Elapsed time (in microseconds) used by this cursor for parsing, executing, and fetching. If the cursor uses parallel execution, then ELAPSED_TIME is the cumulative time for the query coordinator, plus all parallel query slave processes.
OUTLINE_SID
VARCHAR2(40)
Outline session identifier
LAST_ACTIVE_CHILD_ADDRESS
RAW(4 | 8)
Address (identifier) of the child cursor that was the last to be active in the group (that is, the child cursor on behalf of which statistics in V$SQL were updated)
REMOTE
VARCHAR2(1)
Indicates whether the cursor is remote mapped (Y) or not (N)
OBJECT_STATUS
VARCHAR2(19)
Status of the cursor:
VALID - Valid, authorized without errors
VALID_AUTH_ERROR - Valid, authorized with authorization errors
VALID_COMPILE_ERROR - Valid, authorized with compilation errors
VALID_UNAUTH - Valid, unauthorized
INVALID_UNAUTH - Invalid, unauthorized
INVALID - Invalid, unauthorized but keep the timestamp
LITERAL_HASH_VALUE
NUMBER
Hash value of the literals which are replaced with system-generated bind variables and are to be matched, when CURSOR_SHARING is used. This is not the hash value for the SQL statement. If CURSOR_SHARING is not used, then the value is 0.
LAST_LOAD_TIME
DATE
Time at which the query plan was loaded into the library cache
IS_OBSOLETE
VARCHAR2(1)
Indicates whether the cursor has become obsolete (Y) or not (N). This can happen if the number of child cursors is too large.
IS_BIND_SENSITIVE
VARCHAR2(1)
Indicates whether the cursor is bind sensitive (Y) or not (N). A query is considered bind-sensitive if the optimizer peeked at one of its bind variable values when computing predicate selectivities and where a change in a bind variable value may cause the optimizer to generate a different plan.
IS_BIND_AWARE
VARCHAR2(1)
Indicates whether the cursor is bind aware (Y) or not (N). A query is considered bind-aware if it has been marked to use extended cursor sharing. The query would already have been marked as bind-sensitive.
CHILD_LATCH
NUMBER
Child latch number that is protecting the cursor. This column is obsolete and maintained for backward compatibility.
SQL_PROFILE
VARCHAR2(64)
SQL profile used for this statement, if any
SQL_PATCH
VARCHAR2(30)
SQL patch used for this statement, if any
SQL_PLAN_BASELINE
VARCHAR2(30)
SQL plan baseline used for this statement, if any
PROGRAM_ID
NUMBER
Program identifier
PROGRAM_LINE#
NUMBER
Program line number
EXACT_MATCHING_SIGNATURE
NUMBER
Signature used when the CURSOR_SHARING parameter is set to EXACT
FORCE_MATCHING_SIGNATURE
NUMBER
Signature used when the CURSOR_SHARING parameter is set to FORCE
LAST_ACTIVE_TIME
DATE
Time at which the query plan was last active
BIND_DATA
RAW(2000)
Bind data
TYPECHECK_MEM
NUMBER
Typecheck memory
IO_CELL_OFFLOAD_ELIGIBLE_BYTES
NUMBER
Number of I/O bytes which can be filtered by the Exadata storage system
See Also: Oracle Exadata Storage Server Software documentation for more information
IO_INTERCONNECT_BYTES
NUMBER
Number of I/O bytes exchanged between Oracle Database and the storage system
PHYSICAL_READ_REQUESTS
NUMBER
Number of physical read I/O requests issued by the monitored SQL
PHYSICAL_READ_BYTES
NUMBER
Number of bytes read from disks by the monitored SQL
PHYSICAL_WRITE_REQUESTS
NUMBER
Number of physical write I/O requests issued by the monitored SQL
PHYSICAL_WRITE_BYTES
NUMBER
Number of bytes written to disks by the monitored SQL
OPTIMIZED_PHY_READ_REQUESTS
NUMBER
Number of physical read I/O requests from Database Smart Flash Cache issued by the monitored SQL
LOCKED_TOTAL
NUMBER
Total number of times the child cursor has been locked
PINNED_TOTAL
NUMBER
Total number of times the child cursor has been pinned
IO_CELL_UNCOMPRESSED_BYTES
NUMBER
Number of uncompressed bytes (that is, size after decompression) that are offloaded to the Exadata cells
See Also: Oracle Exadata Storage Server Software documentation for more information
IO_CELL_OFFLOAD_RETURNED_BYTES
NUMBER
Number of bytes that are returned by Exadata cell through the regular I/O path
See Also: Oracle Exadata Storage Server Software documentation for more information
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
IS_REOPTIMIZABLE
VARCHAR2(1)
This columns shows whether the next execution matching this child cursor will trigger a reoptimization. The values are:
Y: If the next execution will trigger a reoptimization
R: If the child cursor contains reoptimization information, but will not trigger reoptimization because the cursor was compiled in reporting mode
N: If the child cursor has no reoptimization information
IS_RESOLVED_ADAPTIVE_PLAN
VARCHAR2(1)
This column shows whether all of the adaptive parts of a plan have been resolved to the final plan. Once the plan is resolved, the plan hash value and the plan displayed by DBMS_XPLAN will not change through the end of execution. The values for this column are:
NULL: If the plan is not adaptive
Y: If the plan is fully resolved
N: If the plan is not yet fully resolved
See Also: Oracle Database PL/SQL Packages and Types Reference for more information about the DBMS_XPLAN package
2.1 sql包含的要素
sql在Oracle看来，不是简单的sql语句，还应该包含
sql语句内存(成本)执行次数(效果，被缓存的sql应该要被多次执行，否则被消耗的内存没有发挥价值)cost:物理读、缓存读；环境：优化器配置、schema、客户端等。
3.疑问和解释
3.1 cursor、parent cursor、child cursor？
cursor：是library cache中的内存区域。sql要执行，先分配内存。 parent cursor：保存sql文本。每一个相同的sql文本对应1个parent cursor。即如果sql文本一致，会划入到1个parent cursor中。 child cursor：保存除sql文本外的其他内容。涉及sql运行原理，相同的sql文本，在schema、优化器参数、绑定变量大改时，其实本质是不一样的。child cursor就保存了这些信息。
This is by Oracle database design that you have two kinds of cursors: Parent and Child. For each SQL statement that you execute, Oracle engine will generate two cursors: parent and child cursor. Two cursors are generated because for the same SQL statement, there could be other differences like there can be different bind values or two different schema or different literals values, etc. The parent Cursor will hold the SQL statement and the child cursor will hold the information related to the differences. This essentially makes child cursor as deciding factor as to SQL statement will go for hard or soft parse. 参考：http://expertoracle.com/2017/11/17/db-tuning-basics-3-parent-and-child-cursors/
3.2 v$sql与v$sqlarea的区别
v$sql：V$SQL lists statistics on shared SQL area without the GROUP BY clause and contains one row for each child of the original SQL text entered. 是针对每个child的统计信息，顾 v$sqlarea：V$SQLAREA displays statistics on shared SQL areas and contains one row per SQL string. It provides statistics on SQL statements that are in memory, parsed, and ready for execution. 是针对每个sql文本，即parent的统计信息。
4.应用场景
4.1 应用操作对应的SQL分析
一些系统是黑盒的，没有源码，想知道数据流程，可以通过监控v$sql里缓存的sql分析。
4.2 优化类：sql统计信息的使用
1）top耗资源的进程对应的sql内容
select t.SQL_ID,
t.SERIAL#,
t.USERNAME,
t.SQL_ID,
a.SQL_TEXT,
a.SQL_FULLTEXT
from v$session t, v$process s, v$sqlarea a
where t.PADDR = s.ADDR
and s.SPID in (’18348‘)
and a.SQL_ID = t.SQL_ID;
2）查看最耗时的sql、最消耗磁盘读取的sql等。