[SERVER-19593] Allow collscans on $snapshot queries when not using MMAP1 Created: 24/Jul/15 Updated: 22/Mar/17 Resolved: 06/Aug/15 |
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| Status: | Closed |
| Project: | Core Server |
| Component/s: | Querying |
| Affects Version/s: | 3.0.0 |
| Fix Version/s: | 3.1.7 |
| Type: | Improvement | Priority: | Major - P3 |
| Reporter: | Mathias Stearn | Assignee: | Qingyang Chen |
| Resolution: | Done | Votes: | 0 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Issue Links: |
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| Backwards Compatibility: | Minor Change | ||||||||||||||||||||||||
| Sprint: | Quint Iteration 7 | ||||||||||||||||||||||||
| Participants: | |||||||||||||||||||||||||
| Description |
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In MMAPv1 we need to scan the _id index to ensure we see documents once since records can move in the collection, allowing us to see duplicates or miss documents. In other storage engines this is not allowed, so we should be able to do table scans rather than index scans which can be orders of magnitude slower. This would result in a user-facing change since we would no longer be returning documents in _id order, but that is not part of the documented behavior of $snapshot. |
| Comments |
| Comment by Githook User [ 27/Jan/16 ] |
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Author: {u'username': u'ksuarz', u'name': u'Kyle Suarez', u'email': u'ksuarz@gmail.com'}Message: Due to This removes the description of the implementation of cursor.snapshot(). It also Signed-off-by: kay <kay.kim@10gen.com> |
| Comment by Githook User [ 06/Aug/15 ] |
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Author: {u'username': u'coollog', u'name': u'Qingyang Chen', u'email': u'qingyang.chen@10gen.com'}Message: |
| Comment by Qingyang Chen [ 28/Jul/15 ] |
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Method: |