收缩索引_拆分索引 未完

The shrink index API allows you to shrink an existing index into a new index with fewer primary shards. The requested number of primary shards in the target index must be a factor of the number of shards in the source index.

For example an index with 8 primary shards can be shrunk into 4, 2 or 1 primary shards or an index with 15 primary shards can be shrunk into 5, 3 or 1. If the number of shards in the index is a prime number it can only be shrunk into a single primary shard. Before shrinking, a (primary or replica) copy of every shard in the index must be present on the same node.

Shrinking works as follows:

• First, it creates a new target index with the same definition as the source index, but with a smaller number of primary shards.
• 第一，创建一个新的目标索引，其定义与源索引一致，但是分片比主分片要少。
• Then it hard-links segments from the source index into the target index. (If the file system doesn’t support hard-linking, then all segments are copied into the new index, which is a much more time consuming process.)
• 然后，硬链接源索引的段到目标索引
• Finally, it recovers the target index as though it were a closed index which had just been re-opened.
• 最后，恢复目标索引，就好像他是一个关闭的索引被重新打开