batch.pot

hibernate-distribution-3.3.1.GA-dist.zip源码

# SOME DESCRIPTIVE TITLE.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: PACKAGE VERSION\n"
"Report-Msgid-Bugs-To: http://bugs.kde.org\n"
"POT-Creation-Date: 2008-08-14 15:28+0000\n"
"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
"Language-Team: LANGUAGE <[e-mail]>\n"
"MIME-Version: 1.0\n"
"Content-Type: application/x-xml2pot; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"

#. Tag: title
#: batch.xml:29
#, no-c-format
msgid "Batch processing"
msgstr ""

#. Tag: para
#: batch.xml:31
#, no-c-format
msgid "A naive approach to inserting 100 000 rows in the database using Hibernate might look like this:"
msgstr ""

#. Tag: programlisting
#: batch.xml:36
#, no-c-format
msgid ""
      "<![CDATA[Session session = sessionFactory.openSession();\n"
      "Transaction tx = session.beginTransaction();\n"
      "for ( int i=0; i<100000; i++ ) {\n"
      "    Customer customer = new Customer(.....);\n"
      "    session.save(customer);\n"
      "}\n"
      "tx.commit();\n"
      "session.close();]]>"
msgstr ""

#. Tag: para
#: batch.xml:38
#, no-c-format
msgid "This would fall over with an <literal>OutOfMemoryException</literal> somewhere around the 50 000th row. That's because Hibernate caches all the newly inserted <literal>Customer</literal> instances in the session-level cache."
msgstr ""

#. Tag: para
#: batch.xml:44
#, no-c-format
msgid "In this chapter we'll show you how to avoid this problem. First, however, if you are doing batch processing, it is absolutely critical that you enable the use of JDBC batching, if you intend to achieve reasonable performance. Set the JDBC batch size to a reasonable number (say, 10-50):"
msgstr ""

#. Tag: programlisting
#: batch.xml:51
#, no-c-format
msgid "<![CDATA[hibernate.jdbc.batch_size 20]]>"
msgstr ""

#. Tag: para
#: batch.xml:53
#, no-c-format
msgid "Note that Hibernate disables insert batching at the JDBC level transparently if you use an <literal>identiy</literal> identifier generator."
msgstr ""

#. Tag: para
#: batch.xml:58
#, no-c-format
msgid "You also might like to do this kind of work in a process where interaction with the second-level cache is completely disabled:"
msgstr ""

#. Tag: programlisting
#: batch.xml:63
#, no-c-format
msgid "<![CDATA[hibernate.cache.use_second_level_cache false]]>"
msgstr ""

#. Tag: para
#: batch.xml:65
#, no-c-format
msgid "However, this is not absolutely necessary, since we can explicitly set the <literal>CacheMode</literal> to disable interaction with the second-level cache."
msgstr ""

#. Tag: title
#: batch.xml:71
#, no-c-format
msgid "Batch inserts"
msgstr ""

#. Tag: para
#: batch.xml:73
#, no-c-format
msgid "When making new objects persistent, you must <literal>flush()</literal> and then <literal>clear()</literal> the session regularly, to control the size of the first-level cache."
msgstr ""

#. Tag: programlisting
#: batch.xml:79
#, no-c-format
msgid ""
      "<![CDATA[Session session = sessionFactory.openSession();\n"
      "Transaction tx = session.beginTransaction();\n"
      "   \n"
      "for ( int i=0; i<100000; i++ ) {\n"
      "    Customer customer = new Customer(.....);\n"
      "    session.save(customer);\n"
      "    if ( i % 20 == 0 ) { //20, same as the JDBC batch size\n"
      "        //flush a batch of inserts and release memory:\n"
      "        session.flush();\n"
      "        session.clear();\n"
      "    }\n"
      "}\n"
      "   \n"
      "tx.commit();\n"
      "session.close();]]>"
msgstr ""

#. Tag: title
#: batch.xml:84
#, no-c-format
msgid "Batch updates"
msgstr ""

#. Tag: para
#: batch.xml:86
#, no-c-format
msgid "For retrieving and updating data the same ideas apply. In addition, you need to use <literal>scroll()</literal> to take advantage of server-side cursors for queries that return many rows of data."
msgstr ""

#. Tag: programlisting
#: batch.xml:92
#, no-c-format
msgid ""
      "<![CDATA[Session session = sessionFactory.openSession();\n"
      "Transaction tx = session.beginTransaction();\n"
      "   \n"
      "ScrollableResults customers = session.getNamedQuery(\"GetCustomers\")\n"
      "    .setCacheMode(CacheMode.IGNORE)\n"
      "    .scroll(ScrollMode.FORWARD_ONLY);\n"
      "int count=0;\n"
      "while ( customers.next() ) {\n"
      "    Customer customer = (Customer) customers.get(0);\n"
      "    customer.updateStuff(...);\n"
      "    if ( ++count % 20 == 0 ) {\n"
      "        //flush a batch of updates and release memory:\n"
      "        session.flush();\n"
      "        session.clear();\n"
      "    }\n"
      "}\n"
      "   \n"
      "tx.commit();\n"
      "session.close();]]>"
msgstr ""

#. Tag: title
#: batch.xml:97
#, no-c-format
msgid "The StatelessSession interface"
msgstr ""

#. Tag: para
#: batch.xml:98
#, no-c-format
msgid "Alternatively, Hibernate provides a command-oriented API that may be used for streaming data to and from the database in the form of detached objects. A <literal>StatelessSession</literal> has no persistence context associated with it and does not provide many of the higher-level life cycle semantics. In particular, a stateless session does not implement a first-level cache nor interact with any second-level or query cache. It does not implement transactional write-behind or automatic dirty checking. Operations performed using a stateless session do not ever cascade to associated instances. Collections are ignored by a stateless session. Operations performed via a stateless session bypass Hibernate's event model and interceptors. Stateless sessions are vulnerable to data aliasing effects, due to the lack of a first-level cache. A stateless session is a lower-level abstraction, much closer to the underlying JDBC."
msgstr ""

#. Tag: programlisting
#: batch.xml:113
#, no-c-format
msgid ""
      "<![CDATA[StatelessSession session = sessionFactory.openStatelessSession();\n"
      "Transaction tx = session.beginTransaction();\n"
      "   \n"
      "ScrollableResults customers = session.getNamedQuery(\"GetCustomers\")\n"
      "    .scroll(ScrollMode.FORWARD_ONLY);\n"
      "while ( customers.next() ) {\n"
      "    Customer customer = (Customer) customers.get(0);\n"
      "    customer.updateStuff(...);\n"
      "    session.update(customer);\n"
      "}\n"
      "   \n"
      "tx.commit();\n"
      "session.close();]]>"
msgstr ""

#. Tag: para
#: batch.xml:115