solr的软提交和硬提交

在solr4.0中增加了软提交，加快了index速度，具体如下：

A commit operation makes index changes visible to new search requests.A hard commit also calls fsync on the index files to ensure they have been flushed to stable storage and no data loss will result from a power failure.

A soft commit is much faster since it only makes index changes visible and does not fsync index files or write a new index descriptor. If the JVM crashes or there is a loss of power, changes that occurred after the lasthard commit will be lost. Search collections that have near-real-time requirements (that want index changes to be quickly visible to searches) will want to soft commit often but hard commit less frequently.

An optimize is like a hard commit except that it forces all of the index segments to be merged into a single segment first. Depending on the use cases, this operation should be performed infrequently (like nightly), if at all, since it is very expensive and involves reading and re-writing theentire index. Segments are normally merged over time anyway (as determined by the merge policy), and optimize just forces these merges to occur immediately.

Example:

• <commit/><optimize/>

Optional attributes for "commit" and "optimize"

• waitFlush = "true" | "false" — default is true — block until index changes are flushed to diskSolr1.4 At least in Solr 1.4 and later (perhaps earlier as well), this command has no affect. InSolr4.0 it will be removed.

• waitSearcher = "true" | "false" — default is true — block until a new searcher is opened and registered as the main query searcher, making the changes visible.

• softCommit = "true" | "false" — default is false — perform a soft commit - this will refresh the 'view' of the index in a more performant manner, but without "on-disk" guarantees.Solr4.0

Optional attributes for "commit"

• expungeDeletes = "true" | "false" — default is false — merge segments with deletes away.Solr1.4

Optional attributes for "optimize"

• maxSegments = N — default is '1' — optimizes down to at most this number of segmentsSolr1.3

Example of "commit" and "optimize" with optional attributes

<commit waitSearcher="false"/><commit waitSearcher="false" expungeDeletes="true"/><optimize waitSearcher="false"/>