Types of Crawl in SharePoint Search 2013

In SharePoint search the most of time people annoying that actual content and search content not in Sync. So the search administrator keeps hitting head on the wall and putting same excuse in front of stakeholders “please wait for the next incremental crawl, most of the time :)”. As we know we already have two content crawling methods first is “Full Crawl” and second is “Incremental crawl”.

Disadvantage of the “Full Crawl” and “Incremental Crawl” as both can’t run in a parallel i.e. the content change during the crawl, it required next incremental crawl.

So what is new in continues crawl?

The content source that using continues crawl that run in parallel. The default waiting time is 15 min. So the default wait time can change via PowerShell , no UI for that. Now the content is up to date most of the time. This crawler only for SharePoint content source, so the job of the SharePoint administrator need to identify those content which are keep updating on the regular interval & also comes under the part of search need to be comes under “Continues crawl “category.

The "Continuous Crawl" is a type of crawl that aims to maintain the index as current as possible. So the following are list of crawl are available in SharePoint 2013 search architecture.

1. Run By User
• Full Crawl
• Incremental Crawl
• Continues crawl
2. Run By system (automated crawl)
• Incremental Crawl (clean-up)

1. Run by User: The content source created by user/Administrator and it is trigger/ scheduled by the user. 
• Full Crawl: 
• Crawl full items
• Can be scheduled
• Can be stop and paused
• When required
• Change content access account
• Added new manage properties
• Content enrichment web service codes change/modified.
• Add new IFilter
• Incremental Crawl:
• Crawl last modified content
• Can be scheduled
• Can be stop and paused
• When required
• Crawl last modified content 
• Continues Crawl
• Index as current as possible.
• Cannot be scheduled
• Cannot be stop and paused (Once started, a "Continuous Crawl" can’t be paused or stopped, you can just disable it.)
• When required
• Content frequently changed (Multiple instance can be run in parallel).
• Only for SharePoint Content Source
• E-commerce site in crass site publishing mode.
2. Run by System: The crawl run automatically by the timer job.
• Clean-Up continues crawl (Microsoft definition): A continuous crawl does not process or retry items that return errors more than three times. A "clean-up" incremental crawl automatically runs every four hours for content sources that have continuous crawl enabled to re-crawl any items that repeatedly return errors. This incremental crawl will try to crawl the item again and then will postpone retries if the error persists.

Read more : http://social.technet.microsoft.com/wiki/contents/articles/15571.sharepoint-2013-continuous-crawl-and-the-difference-between-incremental-and-continuous-crawl.aspx