[SERVER-2488] MapReduce should have an option to specify field list to take advantage of covered index Created: 06/Feb/11 Updated: 18/Feb/11 Resolved: 18/Feb/11 |
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| Status: | Closed |
| Project: | Core Server |
| Component/s: | Querying |
| Affects Version/s: | 1.7.5 |
| Fix Version/s: | None |
| Type: | Improvement | Priority: | Minor - P4 |
| Reporter: | Testo | Assignee: | Unassigned |
| Resolution: | Won't Fix | Votes: | 0 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Participants: |
| Description |
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MapReduce should have an option to specify field list to take advantage of covered index. |
| Comments |
| Comment by Eliot Horowitz (Inactive) [ 18/Feb/11 ] |
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| Comment by Scott Hernandez (Inactive) [ 06/Feb/11 ] |
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Map/Reduce doesn't work that way. It gets the whole document and isn't limited by indexes, or the values in them. What you are suggesting would cause map/reduce to behave differently when using an index or not. There is no way to know if the map code requires more fields than are in the index, which is used for document selection not population. Also, things like arrays would not work as the index breaks them apart removing dups. You might want to watch the new aggregation issue: http://jira.mongodb.org/browse/SERVER-447 |