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ClickHouse/docs/zh/faq/general.md

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add faq zh translate (#3323) * add faq zh translate * add faq zh translate --> remove soft md link * add faq zh translate --> add apache hadoop link
2018-10-09 06:53:47 +00:00
# 常见问题
## 为什么不使用MapReduce之类的产品呢?
Doc fixes: remove double placeholders; add them where missing. (#3923) * Doc fix: add spaces where missing * Doc fixes: rm double spaces * Doc fixes: edit spaces * Doc fixes: rm double spaces in /fa * Revert "Doc fixes: rm double spaces in /fa" This reverts commit bb879a62ef5fa965d989fea3b1b2a693d2016a2d. * Doc fix: resolve all problems with double spaces in /fa * Doc fix: add spaces for readability * Doc fix: add spaces * Fix spaces
2018-12-25 15:25:43 +00:00
我们可以将MapReduce这类的系统称为分布式计算系统，其reduce操作基于分布式排序。其中最常见的开源解决方案是 [Apache Hadoop](http://hadoop.apache.org)。 Yandex使用他们的内部解决方案YT。
add faq zh translate (#3323) * add faq zh translate * add faq zh translate --> remove soft md link * add faq zh translate --> add apache hadoop link
2018-10-09 06:53:47 +00:00
这些系统不适合在线查询，因为它们的延迟高。换句话说，它们不能用作Web接口的后端服务。这些系统对于实时数据更新是没有用的。如果操作的结果和所有中间结果（如果有的话）位于单个服务器的内存中，则分布式排序不是执行reduce操作的最佳方式，但这通常是在线查询的情况。在这种情况下，哈希表是执行reduce操作的最佳方式。优化map-reduce任务的常用方法是使用内存中的哈希表进行预聚合（部分reduce），用户手动执行此优化操作。分布式排序是运行简单map-reduce任务时性能降低的主要原因之一。
大多数MapReduce系统允许您在集群上执行任意代码。但是，声明性查询语言更适合OLAP，以便快速运行实验。例如，Hadoop包含Hive和Pig，Cloudera Impala或Shark（过时）for Spark，以及Spark SQL、Presto和Apache Drill。与专业系统相比，运行此类任务时的性能非常不理想，所以将这些系统用作Web接口的后端服务是不现实的，因为延迟相对较高。
WIP on docs/website (#3383) * CLICKHOUSE-4063: less manual html @ index.md * CLICKHOUSE-4063: recommend markdown="1" in README.md * CLICKHOUSE-4003: manually purge custom.css for now * CLICKHOUSE-4064: expand <details> before any print (including to pdf) * CLICKHOUSE-3927: rearrange interfaces/formats.md a bit * CLICKHOUSE-3306: add few http headers * Remove copy-paste introduced in #3392 * Hopefully better chinese fonts #3392 * get rid of tabs @ custom.css * Apply comments and patch from #3384 * Add jdbc.md to ToC and some translation, though it still looks badly incomplete * minor punctuation * Add some backlinks to official website from mirrors that just blindly take markdown sources * Do not make fonts extra light * find . -name '*.md' -type f | xargs -I{} perl -pi -e 's//g' {} * find . -name '*.md' -type f | xargs -I{} perl -pi -e 's/ sql/g' {} * Remove outdated stuff from roadmap.md * Not so light font on front page too * Refactor Chinese formats.md to match recent changes in other languages
2018-10-16 10:47:17 +00:00
DOCAPI-3822: Added faq article into the chinese version.
2019-04-24 08:30:08 +00:00
## What to do if I have a problem with encodings when using Oracle through ODBC? {#oracle-odbc-encodings}
If you use Oracle through ODBC driver as a source of external dictionaries, you need to set up correctly value for the `NLS_LANG` variable in the `/etc/default/clickhouse`. For more details see the [Oracle NLS_LANG FAQ](https://www.oracle.com/technetwork/products/globalization/nls-lang-099431.html).
**Example**
```
DOCAPI-3822: Some corrections.
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NLS_LANG=CHINESE_CHINA.ZHS16GBK
DOCAPI-3822: Added faq article into the chinese version.
2019-04-24 08:30:08 +00:00
```
Domain change in docs
2020-01-30 10:34:55 +00:00
[来源文章](https://clickhouse.tech/docs/zh/faq/general/) <!--hide-->
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