solr optimize - yaokun123/php-wiki GitHub Wiki
大家都知道，solr在提交索引的时候有commit和optimize的概念，今天来分析一下：
当你像solr提交索引更新时，只有运行了commit，索引才会发生变化。当然也并不意味着你每次提交都要commit 如果不是那么紧急，你可以多次提交之后，再执行commit操作。
The <commit> operation writes all documents loaded since the last commit to one or more segment files on
the disk. Before a commit has been issued, newly indexed content is not visible to searches. The commit
operation opens a new searcher, and triggers any event listeners that have been configured.
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commit操作将所有需要更新的文档全部写入索引中，但是新进入的索引不会立即生效。
optimize有点像硬盘上整理磁盘碎片的操作。为了提高搜索速度，它会将索引重组在一起， 然后移除需要被删除删除或是更新的文档，请注意，solr是没有update的这种操作的，只有增加与删除。 solr在优化时，将需要删除或是被替换的索引标记为deleted，然后再创建新的文档替换掉需要被替换的。 optimize就是执行此操作。所以在优化的时候，你的索引会增大，然后再减小。 optimize操作会创建一个全新的的索引结构，所以，你需要预备出2倍于你commit时索引大小的空间。
The <optimize> operation requests Solr to merge internal data structures in order to improve search
performance. For a large index, optimization will take some time to complete, but by merging many small
segment files into a larger one, search performance will improve. If you are using Solr’s replication mechanism
to distribute searches across many systems, be aware that after an optimize, a complete index will need to be
transferred. In contrast, post-commit transfers are usually much smaller.
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optimize操作是合并内部的数据结构来提供搜索性能。对于大型的索引，optimize耗时较多，
但是通过合并一些索引结构，到一个大的，那么索引性能会得到提高，需要注意的是一个完整的索引需要传送，
对比来说，以post方式进行的提交会更小。
参考：http://xiaofeng.iteye.com/blog/1299148
此外，他解释一些运行参数：
| Optional Attribute | Description |
|---|---|
| waitSearch | Default is true. Blocks until a new searcher is opened and registered as the main query searcher, making the changes visible |
| expungeDeletes | (commit only)Default is false. Merges segments that have more than 10% deleted docs,expunging them in the process. |
| maxSegments | (optimize only)Default is 1. Merges the segments down to no more than this number of segments |