真实案例的情况是:SQL正常执行时间3.4分钟,某天TV表delete一些记录后,执行了将近20分钟还没有完成,而其中最重要的变化就是执行计划其中的一个hash join变成了nested loops,虽然hint中已经指定全部表要use_hash。 这个模拟的SQL展示的就是真实案例出现异常的情况。其中一个步骤使用了nested loops,大概要执行4分钟左右才...
只有在数据库初始化参数HASH_JOIN_ENABLED设为True,并且为参数PGA_AGGREGATE_TARGET设置了一个足够大的值的时候,Oracle才会使用哈希边连接(HASH_AREA_SIZE是向下兼容的参数,但在Oracle9i之前的版本中应当使用HASH_AREA_SIZE)。这和嵌套循环连接有点类似——Oracle先建立一张哈希表以利于操作进行。当使用ORDERED提示时,FR...
Using USE_HASH hint I resolved network bottleneck as much less data was being sent over the network. My colleague was very pleased with query performance improvement :)
OracleHint(提示)之USE_CONCAT USE_CONCAT提示的作用和使用方法USE_CONCAT提示是指导优化器,在处理where子句中的OR条件时,将每一个OR条件都拆成只包含OR条件中的其中一个的子句,然后将这些子句用UNION ALL联接起来,并去除那些在其它子句中已经出现的记录。USE_CONCAT提示的使用语法如下图所示:其中:tablespec表示目标...
/*+ USE_HASH(TABLE) */ use_hash提示对指定的标志性一个散列连接。将指定的表与其他行源通过哈希连接方式连接起来. 从本质上讲,散列连接是Oracle用以驱动表(最小的表,where 子句中的第一个表)向RAM区中装载纪录 的方法,RAM区是由hash_area_size初始化参数定义
if(!OidIsValid(opclass))ereport(ERROR,(errcode(ERRCODE_UNDEFINED_OBJECT),errmsg("data type %s has no default operator class for access method \"%s\"",format_type_be(attrType),"hash"),errhint("You must specify an operator class or define a default operator class for the data type."))...
I‘m not good at using hiter and I can't understand "_N_ = hi.next();_N_ = hi.prev();“ in your code.Can you give me a hint? 0 Likes Ksharp Super User Re: How to use hash to find the minimum value and minimum date in groups? Posted 08-08-2020...
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We can see that we got the same hashes as before, but we also found a password hint for admin2. Nice. Now if we type creds at the prompt, Metasploit will display all the credentials that are currently stored in the database:
Oracle may find a path that allows it to ignore your hint. In a recent example I found that in: select /*+ use_nl(t2) *./ . . . from t1, t2 etc... the hint was ignored, and a hash join was used, but if I used the hints: ...