[DOCS-5003] mongoexport --forceTableScan description can be misleading Created: 13/Mar/15  Updated: 11/Jan/17  Resolved: 13/Jul/15

Status: Closed
Project: Documentation
Component/s: manual
Affects Version/s: None
Fix Version/s: 01112017-cleanup

Type: Improvement Priority: Major - P3
Reporter: Andrew Ryder (Inactive) Assignee: Unassigned
Resolution: Done Votes: 0
Labels: tools
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:
Days since reply: 8 years, 31 weeks, 2 days ago

 Description   

RE: http://docs.mongodb.org/manual/reference/program/mongoexport/#cmdoption--forceTableScan


When you run with --forceTableScan, mongoexport does not use $snapshot. As a result, the export produced by mongoexport can reflect the state of the database at many different points in time.

The above statement gives the impression that when you use mongoexport normally (without --forceTableScan) it would reflect a single point in time. Which is not true.

mongoexport never reflects a single point in time (unless you stop writes to the database prior to running it), regardless of the use or non-use of --forceTableScan.

--forceTableScan might cause the output to include the same document twice (representing two variants in time) but it does not affect the chances of the output representing a sheared cross-section in time - resulting in a copy of the database which never actually existed.

The only reason that $snapshot (i.e not using --forceTableScan) avoids duplicates in the output is because it walks the unique immutable _id index which cannot possibly result in seeing the same document twice - this is unrelated to a point-in-time though ($snapshot is a misleading name but we're stuck with it).



 Comments   
Comment by Githook User [ 13/Jul/15 ]

Author:

{u'username': u'kay-kim', u'name': u'kay', u'email': u'kay.kim@10gen.com'}

Message: DOCS-5003 clarify forceTableScan for mongoexport
Branch: master
https://github.com/mongodb/docs/commit/9841d1bd6c59ebcc0cdacd4942dd3d554a562953

Comment by Githook User [ 13/Jul/15 ]

Author:

{u'username': u'kay-kim', u'name': u'kay', u'email': u'kay.kim@10gen.com'}

Message: DOCS-5003 clarify forceTableScan for mongoexport
Branch: v2.6
https://github.com/mongodb/docs/commit/7c9d0498cd56d114b1cc410ed66483661ab30d1e

Comment by Githook User [ 13/Jul/15 ]

Author:

{u'username': u'kay-kim', u'name': u'kay', u'email': u'kay.kim@10gen.com'}

Message: DOCS-5003 clarify forceTableScan for mongoexport
Branch: v2.4
https://github.com/mongodb/docs/commit/d0a0d802542bee1eba5e31213eae04e8907c9947

Generated at Thu Feb 08 07:49:22 UTC 2024 using Jira 9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66.