OpenJPA合并/持久化非常慢 [英] OpenJPA merging/persisting is very slow

问题描述

我在带有MySQL 5.0 DB的WebSphere Application Server 8上使用OpenJPA 2.2.0.

I use OpenJPA 2.2.0 on WebSphere Application Server 8 with a MySQL 5.0 DB.

我有一个要合并到数据库中的对象列表.

I have a list of objects which I want to merge into the DB.

就像:

for (Object ob : list) {
            Long start = Calendar.getInstance().getTimeInMillis();
            em = factory.createEntityManager();
            em.getTransaction().begin();

            em.merge(ob);

            em.getTransaction().commit();
            em.close();
            Long end = Calendar.getInstance().getTimeInMillis();
            Long diff = end - start;
            LOGGER.info("Time: " + diff);
        }

运行此循环时，我需要大约300-600毫秒来合并一个对象.当我删除"em.merge(ob);"行时那么我需要"0"毫秒来遍历1个列表对象.

When I run this loop I need about 300-600 Milliseconds to merge one object. When I delete the line "em.merge(ob);" then I need "0" Milliseconds to iterate over 1 List Object.

所以我的问题是:我该怎么做才能缩短合并一个对象的时间?

So my question is: What can I do to improve the time to merge one object?

谢谢！

推荐答案

您可以在迭代&之前尝试启动事务.然后在一次交易中将其提交.因此，基本上，您正在创建一个将在提交时合并/持久化的批处理.

You can try starting the transaction before iteration & then commiting it afterwards within a single transaction. So, basically you are creating a batch which would be merged/persisted on commit.

此外，您可以一次限制要处理的批次中的对象数量，可以将更改显式刷新到数据库中.

Also, you can limit the number of objects in a batch to be processed at a time & can explicitly flush the changes into database.

在这里，您正在发起交易&在每次迭代中提交它，以及每次创建/关闭实体管理器都会影响大量数据的性能.

Here, you are initiating a transaction & commiting it in each iteration and also creating/closing entity manager each time, will affect performance for numerous data.

这将类似于下面的代码.

It will be something like below code.

em = factory.createEntityManager();
em.getTransaction().begin();
int i = 0;

   for (Object ob : list) {
       Long start = Calendar.getInstance().getTimeInMillis();

       em.merge(ob);

       Long end = Calendar.getInstance().getTimeInMillis();
       Long diff = end - start;
       LOGGER.info("Time: " + diff);

       /*BATCH_SIZE is the number of entities 
            that will be persisted/merged at once */

       if(i%BATCH_SIZE == 0){    
           em.flush();
           em.clear(); 
       }

       i++;
   }

em.getTransaction().commit();
em.close();

在这里，如果任何对象未能持久/合并，您还可以回滚整个事务.

Here, you can also rollback the whole transaction if any of the object fails to persist/merge.

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