$exists: true could scan any index (but ignore the no-such-field-key if the index is sparse).
$exists: false could scan a non-sparse index for the no-such-field key.
- is duplicated by
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SERVER-12905 {$exists:false} performance regression
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- Closed
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SERVER-12262 Use full index scan as proxy for collection scan in order to make certain queries covered
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- Closed
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- is related to
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SERVER-4187 automatically pick sparse indexes for $exists:true queries
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- Closed
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- related to
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- Backlog
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