Compute space usage of a Searcher / SegmentReader / CompositeFile (#282)

* Compute space usage of a Searcher / SegmentReader / CompositeFile

* Fix typo

* Add serde Serialize/Deserialize for all the SpaceUsage structs

* Fix indexing

* Public methods for consuming space usage information

* #281: Add a space usage method that takes a SegmentComponent to support code that is unaware of particular segment components, and to make it more likely to update methods when a new component type is added.

* Add support for space usage computation of positions skip index file (#281)

* Add some tests for space usage computation (#281)

1 files changed, 12 insertions, 0 deletions

diff --git a/src/common/composite_file.rs b/src/common/composite_file.rs
index e7d657b..0cdfdff 100644
--- a/src/common/composite_file.rs
+++ b/src/common/composite_file.rs
@@ -4,6 +4,8 @@ use common::VInt;
 use directory::ReadOnlySource;
 use directory::WritePtr;
 use schema::Field;
+use space_usage::PerFieldSpaceUsage;
+use space_usage::FieldUsage;
 use std::collections::HashMap;
 use std::io::Write;
 use std::io::{self, Read};
@@ -166,6 +168,16 @@ impl CompositeFile {
             .get(&FileAddr { field, idx })
             .map(|&(from, to)| self.data.slice(from, to))
     }
+
+    pub fn space_usage(&self) -> PerFieldSpaceUsage {
+        let mut fields = HashMap::new();
+        for (&field_addr, &(start, end)) in self.offsets_index.iter() {
+            fields.entry(field_addr.field)
+                .or_insert_with(|| FieldUsage::empty(field_addr.field))
+                .add_field_idx(field_addr.idx, end - start);
+        }
+        PerFieldSpaceUsage::new(fields)
+    }
 }
 
 #[cfg(test)]