Why does Rebuilding a Search Index peg my CPU at 100%?

Question

If I rebuild any search index, whether through Indexing Manager, or programatically, the CPU pegs at 100% until the rebuilding operation completes. This happens on development machines and production server alike. It happens for a custom index as well as sitecore_master_index and sitecore_web_index.

Is this just standard behavior or is there some way the CPU usage can be managed?

Here's the configuration for the custom index:

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <contentSearch>
      <configuration type="Sitecore.ContentSearch.ContentSearchConfiguration, Sitecore.ContentSearch">
        <indexes hint="list:AddIndex">
          <index id="publications_search" type="Sitecore.ContentSearch.LuceneProvider.SwitchOnRebuildLuceneIndex, Sitecore.ContentSearch.LuceneProvider">
            <param desc="name">$(id)</param>
            <param desc="folder">$(id)</param>
            <param desc="propertyStore" ref="contentSearch/indexConfigurations/databasePropertyStore" param1="$(id)" />
            <configuration ref="contentSearch/indexConfigurations/publicationsLuceneIndexConfiguration" />
            <strategies hint="list:AddStrategy">
              <strategy ref="contentSearch/indexConfigurations/indexUpdateStrategies/onPublishEndAsync" />
            </strategies>
            <locations hint="list:AddCrawler">
              <crawler type="Sitecore.ContentSearch.SitecoreItemCrawler, Sitecore.ContentSearch">
                <Database>web</Database>
                <Root>/sitecore/content/Insurance Research Items/Documents</Root>
              </crawler>
            </locations>
          </index>
        </indexes>
      </configuration>
    </contentSearch>
  </sitecore>
</configuration>

Any advice would be helpful, thanks.

Answer 1

Pretty much as expected. Means your disks perform great and you have enough memory.

There is a setting; ContentSearch.ParallelIndexing.Enabled defined in Sitecore.ContentSearch.config you can try setting to "false". It would slow down your index rebuild time, but might make it less intense while running.

See also: https://community.sitecore.net/developers/f/6/t/3620