等待事件enq:HW–contention说明及解决方法

一、今天在查看awr报告中，发现Top 5 Timed Foreground Events发现enq: HW – contention的等待事件；

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免费云主机域名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”>

二、enq: HW – contention的官方说明：

The HW enqueue is used to serialize the allocation of space beyond the high water mark of a segment.

?V$SESSION_WAIT.P2 / V$LOCK.ID1 is the tablespace number.

?V$SESSION_WAIT.P3 / V$LOCK.ID2 is the relative data block address (dba) of segment header of the object for which space is being allocated.

If this is a point of contention for an object, then manual allocation of extents solves the problem.

三、等待事件解释

为防止多个进程同时修改HWM而提供的锁称为HW锁。想要移动HWM的进程必须获得HW锁。若在获取HW锁过程中发生争用，则等待enq: HW – contention事件。HW锁争用大部分是因大量执行insert所引发的，偶尔也会因大量执行update在回滚段中发生HW锁争用现象。若是update，表中段的扩展的大小虽然不多，但在创建回滚数据的过程中，需要回滚段的急速扩张。HW锁争用是在急速空间扩张时普遍出现的等待现象，有时也会引发严重的性能下降。

SQL> select event#,name,parameter1,parameter2,parameter3 from v$event_name where name = ‘enq: HW – contention’;

EVENT# NAME PARAMETER1 PARAMETER2 PARAMETER3

———- —————————————- ——————– ——————– ——————–

250 enq: HW – contention name|mode table space # block

众所周知，Oracle高水位线标志着该线以下的block均被Oracle格式过，通俗一点讲就是该高水位线以下的block都被Oracle使用过。 通常在执行insert操作时，当高水位线以下block不够用时，Oracle将会推进高水位线。更进一步讲，当有多个进程在同时进行insert操作时，比较容易引起高水位线争用，主要表现为enq: HW – contention。

四、如何找到事件：’enq: HW – contention’ 热点对象：

1、查看v$session_wait，应该会有如下等待事件：

SQL> select p1, p2, p3 from v$session_wait where event = ‘enq: HW – contention’;

P1 P2 P3

———- ———- ———-

1213661190 7 140003563

1213661190 7 140003563

1213661190 7 140003563

1213661190 7 140003563

1213661190 7 140003563

1213661190 7 140003563

1213661190 7 140003563

2、通过P3进行DBMS_UTILITY转换可以获知发生争用的文件和block：

SQL> select dbms_utility.data_block_address_block(140003563),dbms_utility.data_block_address_file(140003563) from dual;

DBMS_UTILITY.DATA_BLOCK_ADDRESS_BLOCK(140003563) DBMS_UTILITY.DATA_BLOCK_ADDRESS_FILE(140003563)

———————————————— ———————————————–

1591531 33

3、进而通过file#和block#定位对象：

SQL> select owner, segment_type, segment_name

from dba_extents

where file_id = 33 and 1591531 between block_id and block_id + blocks – 1;

五、减少HW锁争用的方法如下：

If this is a point of contention for an object, then manual allocation of extents solves the problem.

脚本：alter table allocate extent，提前分配空间；

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本文作者：JOHN

ORACLE技术博客：ORACLE 猎人笔记 数据库技术群：367875324 （请备注ORACLE管理 ）

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