Store List of Fields in Segment

Fiels may be encoded in the columnar storage or in the inverted index
for JSON fields.
Add a new Segment file that contains the list of fields (schema +
encoded)

Cargo.toml

@@ -25,7 +25,7 @@ aho-corasick = "1.0"
 tantivy-fst = "0.5"
 memmap2 = { version = "0.9.0", optional = true }
 lz4_flex = { version = "0.11", default-features = false, optional = true }
-zstd = { version = "0.13", optional = true, default-features = false }
+zstd = { version = "0.13", default-features = false }
 tempfile = { version = "3.3.0", optional = true }
 log = "0.4.16"
 serde = { version = "1.0.136", features = ["derive"] }
@@ -105,7 +105,7 @@ mmap = ["fs4", "tempfile", "memmap2"]
 stopwords = []
 
 lz4-compression = ["lz4_flex"]
-zstd-compression = ["zstd"]
+zstd-compression = []
 
 failpoints = ["fail", "fail/failpoints"]
 unstable = [] # useful for benches.

columnar/src/columnar/column_type.rs

@@ -58,7 +58,7 @@ impl ColumnType {
         self == &ColumnType::DateTime
     }
 
-    pub(crate) fn try_from_code(code: u8) -> Result<ColumnType, InvalidData> {
+    pub fn try_from_code(code: u8) -> Result<ColumnType, InvalidData> {
         COLUMN_TYPES.get(code as usize).copied().ok_or(InvalidData)
     }
 }

columnar/src/columnar/writer/mod.rs

@@ -333,7 +333,7 @@ impl ColumnarWriter {
         num_docs: RowId,
         old_to_new_row_ids: Option<&[RowId]>,
         wrt: &mut dyn io::Write,
-    ) -> io::Result<()> {
+    ) -> io::Result<Vec<(String, ColumnType)>> {
         let mut serializer = ColumnarSerializer::new(wrt);
         let mut columns: Vec<(&[u8], ColumnType, Addr)> = self
             .numerical_field_hash_map
@@ -374,7 +374,9 @@ impl ColumnarWriter {
 
         let (arena, buffers, dictionaries) = (&self.arena, &mut self.buffers, &self.dictionaries);
         let mut symbol_byte_buffer: Vec<u8> = Vec::new();
-        for (column_name, column_type, addr) in columns {
+        for (column_name, column_type, addr) in columns.iter() {
+            let column_type = *column_type;
+            let addr = *addr;
             match column_type {
                 ColumnType::Bool => {
                     let column_writer: ColumnWriter = self.bool_field_hash_map.read(addr);
@@ -485,7 +487,15 @@ impl ColumnarWriter {
             };
         }
         serializer.finalize(num_docs)?;
-        Ok(())
+        Ok(columns
+            .into_iter()
+            .map(|(column_name, column_type, _)| {
+                (
+                    String::from_utf8_lossy(column_name).to_string(),
+                    column_type,
+                )
+            })
+            .collect())
     }
 }
 

common/src/bitset.rs

@@ -6,7 +6,7 @@ use ownedbytes::OwnedBytes;
 
 use crate::ByteCount;
 
-#[derive(Clone, Copy, Eq, PartialEq)]
+#[derive(Clone, Copy, Eq, PartialEq, Hash)]
 pub struct TinySet(u64);
 
 impl fmt::Debug for TinySet {

src/core/index_meta.rs

@@ -142,6 +142,7 @@ impl SegmentMeta {
             SegmentComponent::FastFields => ".fast".to_string(),
             SegmentComponent::FieldNorms => ".fieldnorm".to_string(),
             SegmentComponent::Delete => format!(".{}.del", self.delete_opstamp().unwrap_or(0)),
+            SegmentComponent::FieldList => ".fieldlist".to_string(),
         });
         PathBuf::from(path)
     }

src/core/inverted_index_reader.rs

@@ -70,7 +70,7 @@ impl InvertedIndexReader {
         &self.termdict
     }
 
-    /// Return the fields and types encoded in the dictionary in lexicographic oder.
+    /// Return the fields and types encoded in the dictionary in lexicographic order.
     /// Only valid on JSON fields.
     ///
     /// Notice: This requires a full scan and therefore **very expensive**.

src/core/json_utils.rs

@@ -1,4 +1,4 @@
-use columnar::MonotonicallyMappableToU64;
+use columnar::{ColumnType, MonotonicallyMappableToU64};
 use common::{replace_in_place, JsonPathWriter};
 use rustc_hash::FxHashMap;
 
@@ -153,7 +153,7 @@ fn index_json_value<'a, V: Value<'a>>(
                 let mut token_stream = text_analyzer.token_stream(val);
                 let unordered_id = ctx
                     .path_to_unordered_id
-                    .get_or_allocate_unordered_id(json_path_writer.as_str());
+                    .get_or_allocate_unordered_id(json_path_writer.as_str(), ColumnType::Str);
 
                 // TODO: make sure the chain position works out.
                 set_path_id(term_buffer, unordered_id);
@@ -171,7 +171,7 @@ fn index_json_value<'a, V: Value<'a>>(
                 set_path_id(
                     term_buffer,
                     ctx.path_to_unordered_id
-                        .get_or_allocate_unordered_id(json_path_writer.as_str()),
+                        .get_or_allocate_unordered_id(json_path_writer.as_str(), ColumnType::U64),
                 );
                 term_buffer.append_type_and_fast_value(val);
                 postings_writer.subscribe(doc, 0u32, term_buffer, ctx);
@@ -180,7 +180,7 @@ fn index_json_value<'a, V: Value<'a>>(
                 set_path_id(
                     term_buffer,
                     ctx.path_to_unordered_id
-                        .get_or_allocate_unordered_id(json_path_writer.as_str()),
+                        .get_or_allocate_unordered_id(json_path_writer.as_str(), ColumnType::I64),
                 );
                 term_buffer.append_type_and_fast_value(val);
                 postings_writer.subscribe(doc, 0u32, term_buffer, ctx);
@@ -189,7 +189,7 @@ fn index_json_value<'a, V: Value<'a>>(
                 set_path_id(
                     term_buffer,
                     ctx.path_to_unordered_id
-                        .get_or_allocate_unordered_id(json_path_writer.as_str()),
+                        .get_or_allocate_unordered_id(json_path_writer.as_str(), ColumnType::F64),
                 );
                 term_buffer.append_type_and_fast_value(val);
                 postings_writer.subscribe(doc, 0u32, term_buffer, ctx);
@@ -198,7 +198,7 @@ fn index_json_value<'a, V: Value<'a>>(
                 set_path_id(
                     term_buffer,
                     ctx.path_to_unordered_id
-                        .get_or_allocate_unordered_id(json_path_writer.as_str()),
+                        .get_or_allocate_unordered_id(json_path_writer.as_str(), ColumnType::Bool),
                 );
                 term_buffer.append_type_and_fast_value(val);
                 postings_writer.subscribe(doc, 0u32, term_buffer, ctx);
@@ -206,8 +206,10 @@ fn index_json_value<'a, V: Value<'a>>(
             ReferenceValueLeaf::Date(val) => {
                 set_path_id(
                     term_buffer,
-                    ctx.path_to_unordered_id
-                        .get_or_allocate_unordered_id(json_path_writer.as_str()),
+                    ctx.path_to_unordered_id.get_or_allocate_unordered_id(
+                        json_path_writer.as_str(),
+                        ColumnType::DateTime,
+                    ),
                 );
                 term_buffer.append_type_and_fast_value(val);
                 postings_writer.subscribe(doc, 0u32, term_buffer, ctx);

src/core/segment_component.rs

@@ -27,12 +27,14 @@ pub enum SegmentComponent {
     /// Bitset describing which document of the segment is alive.
     /// (It was representing deleted docs but changed to represent alive docs from v0.17)
     Delete,
+    /// Field list describing the fields in the segment.
+    FieldList,
 }
 
 impl SegmentComponent {
     /// Iterates through the components.
     pub fn iterator() -> slice::Iter<'static, SegmentComponent> {
-        static SEGMENT_COMPONENTS: [SegmentComponent; 8] = [
+        static SEGMENT_COMPONENTS: [SegmentComponent; 9] = [
             SegmentComponent::Postings,
             SegmentComponent::Positions,
             SegmentComponent::FastFields,
@@ -41,6 +43,7 @@ impl SegmentComponent {
             SegmentComponent::Store,
             SegmentComponent::TempStore,
             SegmentComponent::Delete,
+            SegmentComponent::FieldList,
         ];
         SEGMENT_COMPONENTS.iter()
     }

src/core/segment_reader.rs

@@ -3,15 +3,14 @@ use std::ops::BitOrAssign;
 use std::sync::{Arc, RwLock};
 use std::{fmt, io};
 
-use fnv::FnvHashMap;
 use itertools::Itertools;
 
 use crate::core::{InvertedIndexReader, Segment, SegmentComponent, SegmentId};
 use crate::directory::{CompositeFile, FileSlice};
 use crate::error::DataCorruption;
 use crate::fastfield::{intersect_alive_bitsets, AliveBitSet, FacetReader, FastFieldReaders};
+use crate::field_list::read_split_fields;
 use crate::fieldnorm::{FieldNormReader, FieldNormReaders};
-use crate::json_utils::json_path_sep_to_dot;
 use crate::schema::{Field, IndexRecordOption, Schema, Type};
 use crate::space_usage::SegmentSpaceUsage;
 use crate::store::StoreReader;
@@ -44,6 +43,7 @@ pub struct SegmentReader {
     fast_fields_readers: FastFieldReaders,
     fieldnorm_readers: FieldNormReaders,
 
+    list_fields_file: Option<FileSlice>, // Optional field list file for backwards compatibility
     store_file: FileSlice,
     alive_bitset_opt: Option<AliveBitSet>,
     schema: Schema,
@@ -153,6 +153,7 @@ impl SegmentReader {
         let termdict_composite = CompositeFile::open(&termdict_file)?;
 
         let store_file = segment.open_read(SegmentComponent::Store)?;
+        let list_fields_file = segment.open_read(SegmentComponent::FieldList).ok();
 
         crate::fail_point!("SegmentReader::open#middle");
 
@@ -201,6 +202,7 @@ impl SegmentReader {
             segment_id: segment.id(),
             delete_opstamp: segment.meta().delete_opstamp(),
             store_file,
+            list_fields_file,
             alive_bitset_opt,
             positions_composite,
             schema,
@@ -299,87 +301,25 @@ impl SegmentReader {
     /// field that is not indexed nor a fast field but is stored, it is possible for the field
     /// to not be listed.
     pub fn fields_metadata(&self) -> crate::Result<Vec<FieldMetadata>> {
-        let mut indexed_fields: Vec<FieldMetadata> = Vec::new();
-        let mut map_to_canonical = FnvHashMap::default();
-        for (field, field_entry) in self.schema().fields() {
-            let field_name = field_entry.name().to_string();
-            let is_indexed = field_entry.is_indexed();
-
-            if is_indexed {
-                let is_json = field_entry.field_type().value_type() == Type::Json;
-                if is_json {
-                    let inv_index = self.inverted_index(field)?;
-                    let encoded_fields_in_index = inv_index.list_encoded_fields()?;
-                    let mut build_path = |field_name: &str, mut json_path: String| {
-                        // In this case we need to map the potential fast field to the field name
-                        // accepted by the query parser.
-                        let create_canonical =
-                            !field_entry.is_expand_dots_enabled() && json_path.contains('.');
-                        if create_canonical {
-                            // Without expand dots enabled dots need to be escaped.
-                            let escaped_json_path = json_path.replace('.', "\\.");
-                            let full_path = format!("{}.{}", field_name, escaped_json_path);
-                            let full_path_unescaped = format!("{}.{}", field_name, &json_path);
-                            map_to_canonical.insert(full_path_unescaped, full_path.to_string());
-                            full_path
-                        } else {
-                            // With expand dots enabled, we can use '.' instead of '\u{1}'.
-                            json_path_sep_to_dot(&mut json_path);
-                            format!("{}.{}", field_name, json_path)
-                        }
-                    };
-                    indexed_fields.extend(
-                        encoded_fields_in_index
-                            .into_iter()
-                            .map(|(name, typ)| (build_path(&field_name, name), typ))
-                            .map(|(field_name, typ)| FieldMetadata {
-                                indexed: true,
-                                stored: false,
-                                field_name,
-                                fast: false,
-                                typ,
-                            }),
-                    );
-                } else {
-                    indexed_fields.push(FieldMetadata {
-                        indexed: true,
-                        stored: false,
-                        field_name: field_name.to_string(),
-                        fast: false,
-                        typ: field_entry.field_type().value_type(),
-                    });
-                }
-            }
+        if let Some(list_fields_file) = self.list_fields_file.as_ref() {
+            let file = list_fields_file.read_bytes()?;
+            let fields_metadata =
+                read_split_fields(file)?.collect::<io::Result<Vec<FieldMetadata>>>();
+            fields_metadata.map_err(|e| e.into())
+        } else {
+            // Schema fallback
+            Ok(self
+                .schema()
+                .fields()
+                .map(|(_field, entry)| FieldMetadata {
+                    field_name: entry.name().to_string(),
+                    typ: entry.field_type().value_type(),
+                    indexed: entry.is_indexed(),
+                    stored: entry.is_stored(),
+                    fast: entry.is_fast(),
+                })
+                .collect())
         }
-        let mut fast_fields: Vec<FieldMetadata> = self
-            .fast_fields()
-            .columnar()
-            .iter_columns()?
-            .map(|(mut field_name, handle)| {
-                json_path_sep_to_dot(&mut field_name);
-                // map to canonical path, to avoid similar but different entries.
-                // Eventually we should just accept '.' seperated for all cases.
-                let field_name = map_to_canonical
-                    .get(&field_name)
-                    .unwrap_or(&field_name)
-                    .to_string();
-                FieldMetadata {
-                    indexed: false,
-                    stored: false,
-                    field_name,
-                    fast: true,
-                    typ: Type::from(handle.column_type()),
-                }
-            })
-            .collect();
-        // Since the type is encoded differently in the fast field and in the inverted index,
-        // the order of the fields is not guaranteed to be the same. Therefore, we sort the fields.
-        // If we are sure that the order is the same, we can remove this sort.
-        indexed_fields.sort_unstable();
-        fast_fields.sort_unstable();
-        let merged = merge_field_meta_data(vec![indexed_fields, fast_fields], &self.schema);
-
-        Ok(merged)
     }
 
     /// Returns the segment id

src/fastfield/writer.rs

@@ -238,13 +238,17 @@ impl FastFieldsWriter {
         mut self,
         wrt: &mut dyn io::Write,
         doc_id_map_opt: Option<&DocIdMapping>,
-    ) -> io::Result<()> {
+    ) -> io::Result<Vec<(String, Type)>> {
         let num_docs = self.num_docs;
         let old_to_new_row_ids =
             doc_id_map_opt.map(|doc_id_mapping| doc_id_mapping.old_to_new_ids());
-        self.columnar_writer
+        let columns = self
+            .columnar_writer
             .serialize(num_docs, old_to_new_row_ids, wrt)?;
-        Ok(())
+        Ok(columns
+            .into_iter()
+            .map(|(field_name, column)| (field_name.to_string(), column.into()))
+            .collect())
     }
 }
 

src/field_list/mod.rs

@@ -0,0 +1,369 @@
+//! The list of fields that are stored in a `tantivy` `Index`.
+
+use std::collections::HashSet;
+use std::io::{self, ErrorKind, Read};
+
+use columnar::ColumnType;
+use common::TinySet;
+use fnv::FnvHashMap;
+
+use crate::indexer::path_to_unordered_id::OrderedPathId;
+use crate::json_utils::json_path_sep_to_dot;
+use crate::postings::IndexingContext;
+use crate::schema::{Field, Schema, Type};
+use crate::{merge_field_meta_data, FieldMetadata, Term};
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)]
+pub(crate) struct FieldConfig {
+    pub typ: Type,
+    pub indexed: bool,
+    pub stored: bool,
+    pub fast: bool,
+}
+
+impl FieldConfig {
+    fn serialize(&self) -> [u8; 2] {
+        let typ = self.typ.to_code();
+        let flags = (self.indexed as u8) << 2 | (self.stored as u8) << 1 | (self.fast as u8);
+        [typ, flags]
+    }
+    fn deserialize_from(data: [u8; 2]) -> io::Result<FieldConfig> {
+        let typ = Type::from_code(data[0]).ok_or_else(|| {
+            io::Error::new(
+                ErrorKind::InvalidData,
+                format!("could not deserialize type {}", data[0]),
+            )
+        })?;
+
+        let data = data[1];
+        let indexed = (data & 0b100) != 0;
+        let stored = (data & 0b010) != 0;
+        let fast = (data & 0b001) != 0;
+
+        Ok(FieldConfig {
+            typ,
+            indexed,
+            stored,
+            fast,
+        })
+    }
+}
+/// Serializes the split fields.
+pub(crate) fn serialize_segment_fields(
+    ctx: IndexingContext,
+    wrt: &mut dyn io::Write,
+    schema: &Schema,
+    unordered_id_to_ordered_id: &[(OrderedPathId, TinySet)],
+    mut columns: Vec<(String, Type)>,
+) -> crate::Result<()> {
+    let mut field_list_set: HashSet<(Field, OrderedPathId, TinySet)> = HashSet::default();
+    let mut encoded_fields = Vec::new();
+    let mut map_to_canonical = FnvHashMap::default();
+
+    // Replace unordered ids by ordered ids to be able to sort
+    let ordered_id_to_path = ctx.path_to_unordered_id.ordered_id_to_path();
+
+    for (key, _addr) in ctx.term_index.iter() {
+        let field = Term::wrap(key).field();
+        let field_entry = schema.get_field_entry(field);
+        if field_entry.field_type().value_type() == Type::Json {
+            let byte_range_unordered_id = 5..5 + 4;
+            let unordered_id =
+                u32::from_be_bytes(key[byte_range_unordered_id.clone()].try_into().unwrap());
+            let (path_id, typ_code_bitvec) = unordered_id_to_ordered_id[unordered_id as usize];
+            if !field_list_set.contains(&(field, path_id, typ_code_bitvec)) {
+                field_list_set.insert((field, path_id, typ_code_bitvec));
+                let mut build_path = |field_name: &str, mut json_path: String| {
+                    // In this case we need to map the potential fast field to the field name
+                    // accepted by the query parser.
+                    let create_canonical =
+                        !field_entry.is_expand_dots_enabled() && json_path.contains('.');
+                    if create_canonical {
+                        // Without expand dots enabled dots need to be escaped.
+                        let escaped_json_path = json_path.replace('.', "\\.");
+                        let full_path = format!("{}.{}", field_name, escaped_json_path);
+                        let full_path_unescaped = format!("{}.{}", field_name, &json_path);
+                        map_to_canonical.insert(full_path_unescaped, full_path.to_string());
+                        full_path
+                    } else {
+                        // With expand dots enabled, we can use '.' instead of '\u{1}'.
+                        json_path_sep_to_dot(&mut json_path);
+                        format!("{}.{}", field_name, json_path)
+                    }
+                };
+
+                let path = build_path(
+                    field_entry.name(),
+                    ordered_id_to_path[path_id.path_id() as usize].to_string(), /* String::from_utf8(key[5..].to_vec()).unwrap(), */
+                );
+                encoded_fields.push((path, typ_code_bitvec));
+            }
+        }
+    }
+
+    let mut indexed_fields: Vec<FieldMetadata> = Vec::new();
+    for (_field, field_entry) in schema.fields() {
+        let field_name = field_entry.name().to_string();
+        let is_indexed = field_entry.is_indexed();
+
+        let is_json = field_entry.field_type().value_type() == Type::Json;
+        if is_indexed && !is_json {
+            indexed_fields.push(FieldMetadata {
+                indexed: true,
+                stored: false,
+                field_name: field_name.to_string(),
+                fast: false,
+                typ: field_entry.field_type().value_type(),
+            });
+        }
+    }
+    for (field_name, field_type_set) in encoded_fields {
+        for field_type in field_type_set {
+            let column_type = ColumnType::try_from_code(field_type as u8).unwrap();
+            indexed_fields.push(FieldMetadata {
+                indexed: true,
+                stored: false,
+                field_name: field_name.to_string(),
+                fast: false,
+                typ: Type::from(column_type),
+            });
+        }
+    }
+    let mut fast_fields: Vec<FieldMetadata> = columns
+        .iter_mut()
+        .map(|(field_name, typ)| {
+            json_path_sep_to_dot(field_name);
+            // map to canonical path, to avoid similar but different entries.
+            // Eventually we should just accept '.' seperated for all cases.
+            let field_name = map_to_canonical
+                .get(field_name)
+                .unwrap_or(field_name)
+                .to_string();
+            FieldMetadata {
+                indexed: false,
+                stored: false,
+                field_name,
+                fast: true,
+                typ: *typ,
+            }
+        })
+        .collect();
+    // Since the type is encoded differently in the fast field and in the inverted index,
+    // the order of the fields is not guaranteed to be the same. Therefore, we sort the fields.
+    // If we are sure that the order is the same, we can remove this sort.
+    indexed_fields.sort_unstable();
+    fast_fields.sort_unstable();
+    let merged = merge_field_meta_data(vec![indexed_fields, fast_fields], schema);
+    let out = serialize_split_fields(&merged);
+    wrt.write_all(&out)?;
+
+    Ok(())
+}
+
+/// Serializes the Split fields.
+///
+/// `fields_metadata` has to be sorted.
+pub fn serialize_split_fields(fields_metadata: &[FieldMetadata]) -> Vec<u8> {
+    // ensure that fields_metadata is strictly sorted.
+    debug_assert!(fields_metadata.windows(2).all(|w| w[0] < w[1]));
+    let mut payload = Vec::new();
+    // Write Num Fields
+    let length = fields_metadata.len() as u32;
+    payload.extend_from_slice(&length.to_le_bytes());
+
+    for field_metadata in fields_metadata {
+        write_field(field_metadata, &mut payload);
+    }
+    let compression_level = 3;
+    let payload_compressed = zstd::stream::encode_all(&mut &payload[..], compression_level)
+        .expect("zstd encoding failed");
+    let mut out = Vec::new();
+    // Write Header -- Format Version
+    let format_version = 1u8;
+    out.push(format_version);
+    // Write Payload
+    out.extend_from_slice(&payload_compressed);
+    out
+}
+
+fn write_field(field_metadata: &FieldMetadata, out: &mut Vec<u8>) {
+    let field_config = FieldConfig {
+        typ: field_metadata.typ,
+        indexed: field_metadata.indexed,
+        stored: field_metadata.stored,
+        fast: field_metadata.fast,
+    };
+
+    // Write Config 2 bytes
+    out.extend_from_slice(&field_config.serialize());
+    let str_length = field_metadata.field_name.len() as u16;
+    // Write String length 2 bytes
+    out.extend_from_slice(&str_length.to_le_bytes());
+    out.extend_from_slice(field_metadata.field_name.as_bytes());
+}
+
+/// Reads a fixed number of bytes into an array and returns the array.
+fn read_exact_array<R: Read, const N: usize>(reader: &mut R) -> io::Result<[u8; N]> {
+    let mut buffer = [0u8; N];
+    reader.read_exact(&mut buffer)?;
+    Ok(buffer)
+}
+
+/// Reads the Split fields from a zstd compressed stream of bytes
+pub fn read_split_fields<R: Read>(
+    mut reader: R,
+) -> io::Result<impl Iterator<Item = io::Result<FieldMetadata>>> {
+    let format_version = read_exact_array::<_, 1>(&mut reader)?[0];
+    assert_eq!(format_version, 1);
+    let reader = zstd::Decoder::new(reader)?;
+    read_split_fields_from_zstd(reader)
+}
+
+fn read_field<R: Read>(reader: &mut R) -> io::Result<FieldMetadata> {
+    // Read FieldConfig (2 bytes)
+    let config_bytes = read_exact_array::<_, 2>(reader)?;
+    let field_config = FieldConfig::deserialize_from(config_bytes)?; // Assuming this returns a Result
+
+    // Read field name length and the field name
+    let name_len = u16::from_le_bytes(read_exact_array::<_, 2>(reader)?) as usize;
+
+    let mut data = vec![0; name_len];
+    reader.read_exact(&mut data)?;
+
+    let field_name = String::from_utf8(data).map_err(|err| {
+        io::Error::new(
+            ErrorKind::InvalidData,
+            format!(
+                "Encountered invalid utf8 when deserializing field name: {}",
+                err
+            ),
+        )
+    })?;
+    Ok(FieldMetadata {
+        field_name,
+        typ: field_config.typ,
+        indexed: field_config.indexed,
+        stored: field_config.stored,
+        fast: field_config.fast,
+    })
+}
+
+/// Reads the Split fields from a stream of bytes
+fn read_split_fields_from_zstd<R: Read>(
+    mut reader: R,
+) -> io::Result<impl Iterator<Item = io::Result<FieldMetadata>>> {
+    let mut num_fields = u32::from_le_bytes(read_exact_array::<_, 4>(&mut reader)?);
+
+    Ok(std::iter::from_fn(move || {
+        if num_fields == 0 {
+            return None;
+        }
+        num_fields -= 1;
+
+        Some(read_field(&mut reader))
+    }))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn field_config_deser_test() {
+        let field_config = FieldConfig {
+            typ: Type::Str,
+            indexed: true,
+            stored: false,
+            fast: true,
+        };
+        let serialized = field_config.serialize();
+        let deserialized = FieldConfig::deserialize_from(serialized).unwrap();
+        assert_eq!(field_config, deserialized);
+    }
+    #[test]
+    fn write_read_field_test() {
+        for typ in Type::iter_values() {
+            let field_metadata = FieldMetadata {
+                field_name: "test".to_string(),
+                typ,
+                indexed: true,
+                stored: true,
+                fast: true,
+            };
+            let mut out = Vec::new();
+            write_field(&field_metadata, &mut out);
+            let deserialized = read_field(&mut &out[..]).unwrap();
+            assert_eq!(field_metadata, deserialized);
+        }
+        let field_metadata = FieldMetadata {
+            field_name: "test".to_string(),
+            typ: Type::Str,
+            indexed: false,
+            stored: true,
+            fast: true,
+        };
+        let mut out = Vec::new();
+        write_field(&field_metadata, &mut out);
+        let deserialized = read_field(&mut &out[..]).unwrap();
+        assert_eq!(field_metadata, deserialized);
+
+        let field_metadata = FieldMetadata {
+            field_name: "test".to_string(),
+            typ: Type::Str,
+            indexed: false,
+            stored: false,
+            fast: true,
+        };
+        let mut out = Vec::new();
+        write_field(&field_metadata, &mut out);
+        let deserialized = read_field(&mut &out[..]).unwrap();
+        assert_eq!(field_metadata, deserialized);
+
+        let field_metadata = FieldMetadata {
+            field_name: "test".to_string(),
+            typ: Type::Str,
+            indexed: true,
+            stored: false,
+            fast: false,
+        };
+        let mut out = Vec::new();
+        write_field(&field_metadata, &mut out);
+        let deserialized = read_field(&mut &out[..]).unwrap();
+        assert_eq!(field_metadata, deserialized);
+    }
+    #[test]
+    fn write_split_fields_test() {
+        let fields_metadata = vec![
+            FieldMetadata {
+                field_name: "test".to_string(),
+                typ: Type::Str,
+                indexed: true,
+                stored: true,
+                fast: true,
+            },
+            FieldMetadata {
+                field_name: "test2".to_string(),
+                typ: Type::Str,
+                indexed: true,
+                stored: false,
+                fast: false,
+            },
+            FieldMetadata {
+                field_name: "test3".to_string(),
+                typ: Type::U64,
+                indexed: true,
+                stored: false,
+                fast: true,
+            },
+        ];
+
+        let out = serialize_split_fields(&fields_metadata);
+
+        let deserialized: Vec<FieldMetadata> = read_split_fields(&mut &out[..])
+            .unwrap()
+            .map(|el| el.unwrap())
+            .collect();
+
+        assert_eq!(fields_metadata, deserialized);
+    }
+}

src/indexer/merger.rs

@@ -1,3 +1,4 @@
+use std::io::Write;
 use std::sync::Arc;
 
 use columnar::{
@@ -13,6 +14,7 @@ use crate::directory::WritePtr;
 use crate::docset::{DocSet, TERMINATED};
 use crate::error::DataCorruption;
 use crate::fastfield::{AliveBitSet, FastFieldNotAvailableError};
+use crate::field_list::serialize_split_fields;
 use crate::fieldnorm::{FieldNormReader, FieldNormReaders, FieldNormsSerializer, FieldNormsWriter};
 use crate::indexer::doc_id_mapping::{MappingType, SegmentDocIdMapping};
 use crate::indexer::SegmentSerializer;
@@ -21,8 +23,8 @@ use crate::schema::{value_type_to_column_type, Field, FieldType, Schema};
 use crate::store::StoreWriter;
 use crate::termdict::{TermMerger, TermOrdinal};
 use crate::{
-    DocAddress, DocId, IndexSettings, IndexSortByField, InvertedIndexReader, Order,
-    SegmentComponent, SegmentOrdinal,
+    merge_field_meta_data, DocAddress, DocId, FieldMetadata, IndexSettings, IndexSortByField,
+    InvertedIndexReader, Order, SegmentComponent, SegmentOrdinal,
 };
 
 /// Segment's max doc must be `< MAX_DOC_LIMIT`.
@@ -255,6 +257,19 @@ impl IndexMerger {
         Ok(())
     }
 
+    fn write_field_list(&self, list_field_wrt: &mut WritePtr) -> crate::Result<()> {
+        let field_metadatas: Vec<Vec<FieldMetadata>> = self
+            .readers
+            .iter()
+            .map(|reader| reader.fields_metadata())
+            .collect::<crate::Result<Vec<_>>>()?;
+        let merged = merge_field_meta_data(field_metadatas, &self.schema);
+        let out = serialize_split_fields(&merged);
+        list_field_wrt.write_all(&out)?;
+
+        Ok(())
+    }
+
     fn write_fast_fields(
         &self,
         fast_field_wrt: &mut WritePtr,
@@ -773,6 +788,7 @@ impl IndexMerger {
         self.write_storable_fields(serializer.get_store_writer(), &doc_id_mapping)?;
         debug!("write-fastfields");
         self.write_fast_fields(serializer.get_fast_field_write(), doc_id_mapping)?;
+        self.write_field_list(serializer.get_field_list_write())?;
 
         debug!("close-serializer");
         serializer.close()?;

src/indexer/path_to_unordered_id.rs

@@ -1,3 +1,5 @@
+use columnar::ColumnType;
+use common::TinySet;
 use fnv::FnvHashMap;
 
 /// `Field` is represented by an unsigned 32-bit integer type.
@@ -24,34 +26,44 @@ impl From<u32> for OrderedPathId {
 
 #[derive(Default)]
 pub(crate) struct PathToUnorderedId {
-    map: FnvHashMap<String, u32>,
+    /// TinySet contains the type codes of the columns in the path.
+    map: FnvHashMap<String, (u32, TinySet)>,
 }
 
 impl PathToUnorderedId {
     #[inline]
-    pub(crate) fn get_or_allocate_unordered_id(&mut self, path: &str) -> u32 {
-        if let Some(id) = self.map.get(path) {
+    pub(crate) fn get_or_allocate_unordered_id(&mut self, path: &str, typ: ColumnType) -> u32 {
+        let code_bit = typ.to_code();
+        if let Some((id, all_codes)) = self.map.get_mut(path) {
+            *all_codes = all_codes.insert(code_bit as u32);
             return *id;
         }
-        self.insert_new_path(path)
+        self.insert_new_path(path, code_bit)
     }
     #[cold]
-    fn insert_new_path(&mut self, path: &str) -> u32 {
+    fn insert_new_path(&mut self, path: &str, typ_code: u8) -> u32 {
         let next_id = self.map.len() as u32;
-        self.map.insert(path.to_string(), next_id);
+        self.map.insert(
+            path.to_string(),
+            (next_id, TinySet::singleton(typ_code as u32)),
+        );
         next_id
     }
 
     /// Retuns ids which reflect the lexical order of the paths.
     ///
     /// The returned vec can be indexed with the unordered id to get the ordered id.
-    pub(crate) fn unordered_id_to_ordered_id(&self) -> Vec<OrderedPathId> {
-        let mut sorted_ids: Vec<(&str, &u32)> =
-            self.map.iter().map(|(k, v)| (k.as_str(), v)).collect();
+    pub(crate) fn unordered_id_to_ordered_id(&self) -> Vec<(OrderedPathId, TinySet)> {
+        let mut sorted_ids: Vec<(&str, (u32, TinySet))> = self
+            .map
+            .iter()
+            .map(|(k, (id, typ_code))| (k.as_str(), (*id, *typ_code)))
+            .collect();
         sorted_ids.sort_unstable_by_key(|(path, _)| *path);
-        let mut result = vec![OrderedPathId::default(); sorted_ids.len()];
-        for (ordered, unordered) in sorted_ids.iter().map(|(_k, v)| v).enumerate() {
-            result[**unordered as usize] = OrderedPathId::from_ordered_id(ordered as u32);
+        let mut result = vec![(OrderedPathId::default(), TinySet::empty()); sorted_ids.len()];
+        for (ordered, (unordered, typ_code)) in sorted_ids.iter().map(|(_k, v)| v).enumerate() {
+            result[*unordered as usize] =
+                (OrderedPathId::from_ordered_id(ordered as u32), *typ_code);
         }
         result
     }
@@ -74,12 +86,12 @@ mod tests {
         let terms = vec!["b", "a", "b", "c"];
         let ids = terms
             .iter()
-            .map(|term| path_to_id.get_or_allocate_unordered_id(term))
+            .map(|term| path_to_id.get_or_allocate_unordered_id(term, ColumnType::Str))
             .collect::<Vec<u32>>();
         assert_eq!(ids, vec![0, 1, 0, 2]);
         let ordered_ids = ids
             .iter()
-            .map(|id| path_to_id.unordered_id_to_ordered_id()[*id as usize])
+            .map(|id| path_to_id.unordered_id_to_ordered_id()[*id as usize].0)
             .collect::<Vec<OrderedPathId>>();
         assert_eq!(ordered_ids, vec![1.into(), 0.into(), 1.into(), 2.into()]);
         // Fetch terms

src/indexer/segment_serializer.rs

@@ -12,6 +12,7 @@ pub struct SegmentSerializer {
     segment: Segment,
     pub(crate) store_writer: StoreWriter,
     fast_field_write: WritePtr,
+    field_list_write: WritePtr,
     fieldnorms_serializer: Option<FieldNormsSerializer>,
     postings_serializer: InvertedIndexSerializer,
 }
@@ -49,6 +50,7 @@ impl SegmentSerializer {
         };
 
         let fast_field_write = segment.open_write(SegmentComponent::FastFields)?;
+        let field_list_write = segment.open_write(SegmentComponent::FieldList)?;
 
         let fieldnorms_write = segment.open_write(SegmentComponent::FieldNorms)?;
         let fieldnorms_serializer = FieldNormsSerializer::from_write(fieldnorms_write)?;
@@ -58,6 +60,7 @@ impl SegmentSerializer {
             segment,
             store_writer,
             fast_field_write,
+            field_list_write,
             fieldnorms_serializer: Some(fieldnorms_serializer),
             postings_serializer,
         })
@@ -81,6 +84,11 @@ impl SegmentSerializer {
         &mut self.postings_serializer
     }
 
+    /// Accessor to the ``.
+    pub fn get_field_list_write(&mut self) -> &mut WritePtr {
+        &mut self.field_list_write
+    }
+
     /// Accessor to the `FastFieldSerializer`.
     pub fn get_fast_field_write(&mut self) -> &mut WritePtr {
         &mut self.fast_field_write
@@ -104,6 +112,7 @@ impl SegmentSerializer {
             fieldnorms_serializer.close()?;
         }
         self.fast_field_write.terminate()?;
+        self.field_list_write.terminate()?;
         self.postings_serializer.close()?;
         self.store_writer.close()?;
         Ok(())

src/indexer/segment_writer.rs

@@ -8,6 +8,7 @@ use super::operation::AddOperation;
 use crate::core::json_utils::index_json_values;
 use crate::core::Segment;
 use crate::fastfield::FastFieldsWriter;
+use crate::field_list::serialize_segment_fields;
 use crate::fieldnorm::{FieldNormReaders, FieldNormsWriter};
 use crate::indexer::segment_serializer::SegmentSerializer;
 use crate::postings::{
@@ -443,16 +444,29 @@ fn remap_and_write(
         .segment()
         .open_read(SegmentComponent::FieldNorms)?;
     let fieldnorm_readers = FieldNormReaders::open(fieldnorm_data)?;
+
+    let unordered_id_to_ordered_id = ctx.path_to_unordered_id.unordered_id_to_ordered_id();
+
     serialize_postings(
-        ctx,
-        schema,
+        &ctx,
+        schema.clone(),
         per_field_postings_writers,
         fieldnorm_readers,
         doc_id_map,
+        &unordered_id_to_ordered_id,
         serializer.get_postings_serializer(),
     )?;
     debug!("fastfield-serialize");
-    fast_field_writers.serialize(serializer.get_fast_field_write(), doc_id_map)?;
+    let columns = fast_field_writers.serialize(serializer.get_fast_field_write(), doc_id_map)?;
+
+    let field_list_serializer = serializer.get_field_list_write();
+    serialize_segment_fields(
+        ctx,
+        field_list_serializer,
+        &schema,
+        &unordered_id_to_ordered_id,
+        columns,
+    )?;
 
     // finalize temp docstore and create version, which reflects the doc_id_map
     if let Some(doc_id_map) = doc_id_map {

src/lib.rs

@@ -188,6 +188,7 @@ pub mod aggregation;
 pub mod collector;
 pub mod directory;
 pub mod fastfield;
+pub mod field_list;
 pub mod fieldnorm;
 pub mod positions;
 pub mod postings;
@@ -238,7 +239,9 @@ pub use crate::schema::DatePrecision;
 pub use crate::schema::{DateOptions, DateTimePrecision, Document, TantivyDocument, Term};
 
 /// Index format version.
-const INDEX_FORMAT_VERSION: u32 = 6;
+///
+/// Version 7: Add `.fieldlist` file containing the list of fields in a segment.
+const INDEX_FORMAT_VERSION: u32 = 7;
 /// Oldest index format version this tantivy version can read.
 const INDEX_FORMAT_OLDEST_SUPPORTED_VERSION: u32 = 4;
 

src/postings/postings_writer.rs

@@ -2,6 +2,7 @@ use std::io;
 use std::marker::PhantomData;
 use std::ops::Range;
 
+use common::TinySet;
 use stacker::Addr;
 
 use crate::fieldnorm::FieldNormReaders;
@@ -46,37 +47,38 @@ fn make_field_partition(
 /// It pushes all term, one field at a time, towards the
 /// postings serializer.
 pub(crate) fn serialize_postings(
-    ctx: IndexingContext,
+    ctx: &IndexingContext,
     schema: Schema,
     per_field_postings_writers: &PerFieldPostingsWriter,
     fieldnorm_readers: FieldNormReaders,
     doc_id_map: Option<&DocIdMapping>,
+    unordered_id_to_ordered_id: &[(OrderedPathId, TinySet)],
     serializer: &mut InvertedIndexSerializer,
 ) -> crate::Result<()> {
     // Replace unordered ids by ordered ids to be able to sort
-    let unordered_id_to_ordered_id: Vec<OrderedPathId> =
-        ctx.path_to_unordered_id.unordered_id_to_ordered_id();
+    let ordered_id_to_path = ctx.path_to_unordered_id.ordered_id_to_path();
 
     let mut term_offsets: Vec<(Field, OrderedPathId, &[u8], Addr)> =
         Vec::with_capacity(ctx.term_index.len());
-    term_offsets.extend(ctx.term_index.iter().map(|(key, addr)| {
+    for (key, addr) in ctx.term_index.iter() {
         let field = Term::wrap(key).field();
-        if schema.get_field_entry(field).field_type().value_type() == Type::Json {
-            let byte_range_path = 5..5 + 4;
-            let unordered_id = u32::from_be_bytes(key[byte_range_path.clone()].try_into().unwrap());
-            let path_id = unordered_id_to_ordered_id[unordered_id as usize];
-            (field, path_id, &key[byte_range_path.end..], addr)
+        let field_entry = schema.get_field_entry(field);
+        if field_entry.field_type().value_type() == Type::Json {
+            let byte_range_unordered_id = 5..5 + 4;
+            let unordered_id =
+                u32::from_be_bytes(key[byte_range_unordered_id.clone()].try_into().unwrap());
+            let (path_id, _typ_code_bitvec) = unordered_id_to_ordered_id[unordered_id as usize];
+            term_offsets.push((field, path_id, &key[byte_range_unordered_id.end..], addr));
         } else {
-            (field, 0.into(), &key[5..], addr)
+            term_offsets.push((field, 0.into(), &key[5..], addr));
         }
-    }));
+    }
     // Sort by field, path, and term
     term_offsets.sort_unstable_by(
         |(field1, path_id1, bytes1, _), (field2, path_id2, bytes2, _)| {
             (field1, path_id1, bytes1).cmp(&(field2, path_id2, bytes2))
         },
     );
-    let ordered_id_to_path = ctx.path_to_unordered_id.ordered_id_to_path();
     let field_offsets = make_field_partition(&term_offsets);
     for (field, byte_offsets) in field_offsets {
         let postings_writer = per_field_postings_writers.get_for_field(field);
@@ -87,7 +89,7 @@ pub(crate) fn serialize_postings(
             &term_offsets[byte_offsets],
             &ordered_id_to_path,
             doc_id_map,
-            &ctx,
+            ctx,
             &mut field_serializer,
         )?;
         field_serializer.close()?;

src/space_usage/mod.rs

@@ -117,6 +117,7 @@ impl SegmentSpaceUsage {
         use self::ComponentSpaceUsage::*;
         use crate::SegmentComponent::*;
         match component {
+            FieldList => ComponentSpaceUsage::Basic(ByteCount::from(0u64)),
             Postings => PerField(self.postings().clone()),
             Positions => PerField(self.positions().clone()),
             FastFields => PerField(self.fast_fields().clone()),