diff --git a/Cargo.lock b/Cargo.lock
index 8676c62f33..81a76954e3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2797,6 +2797,12 @@ version = "0.1.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
 
+[[package]]
+name = "difflib"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -2895,6 +2901,12 @@ version = "0.15.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1aaf95b3e5c8f23aa320147307562d361db0ae0d51242340f558153b4eb2439b"
 
+[[package]]
+name = "downcast"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1435fa1053d8b2fbbe9be7e97eca7f33d37b28409959813daefc1446a14247f1"
+
 [[package]]
 name = "dyn-clone"
 version = "1.0.16"
@@ -3182,6 +3194,15 @@ dependencies = [
  "miniz_oxide",
 ]
 
+[[package]]
+name = "float-cmp"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "98de4bbd547a563b716d8dfa9aad1cb19bfab00f4fa09a6a4ed21dbcf44ce9c4"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -3206,6 +3227,12 @@ dependencies = [
  "regex",
 ]
 
+[[package]]
+name = "fragile"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c2141d6d6c8512188a7891b4b01590a45f6dac67afb4f255c4124dbb86d4eaa"
+
 [[package]]
 name = "frontend"
 version = "0.4.4"
@@ -3913,12 +3940,14 @@ name = "index"
 version = "0.4.4"
 dependencies = [
  "async-trait",
+ "bytemuck",
  "common-base",
  "common-error",
  "common-macro",
  "fst",
  "futures",
  "greptime-proto",
+ "mockall",
  "prost 0.12.2",
  "regex",
  "regex-automata 0.1.10",
@@ -4873,6 +4902,33 @@ dependencies = [
  "uuid",
 ]
 
+[[package]]
+name = "mockall"
+version = "0.11.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4c84490118f2ee2d74570d114f3d0493cbf02790df303d2707606c3e14e07c96"
+dependencies = [
+ "cfg-if 1.0.0",
+ "downcast",
+ "fragile",
+ "lazy_static",
+ "mockall_derive",
+ "predicates",
+ "predicates-tree",
+]
+
+[[package]]
+name = "mockall_derive"
+version = "0.11.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22ce75669015c4f47b289fd4d4f56e894e4c96003ffdf3ac51313126f94c6cbb"
+dependencies = [
+ "cfg-if 1.0.0",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
 [[package]]
 name = "moka"
 version = "0.12.1"
@@ -5101,6 +5157,12 @@ dependencies = [
  "minimal-lexical",
 ]
 
+[[package]]
+name = "normalize-line-endings"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61807f77802ff30975e01f4f071c8ba10c022052f98b3294119f3e615d13e5be"
+
 [[package]]
 name = "nu-ansi-term"
 version = "0.46.0"
@@ -6225,6 +6287,36 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "925383efa346730478fb4838dbe9137d2a47675ad789c546d150a6e1dd4ab31c"
 
+[[package]]
+name = "predicates"
+version = "2.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "59230a63c37f3e18569bdb90e4a89cbf5bf8b06fea0b84e65ea10cc4df47addd"
+dependencies = [
+ "difflib",
+ "float-cmp",
+ "itertools 0.10.5",
+ "normalize-line-endings",
+ "predicates-core",
+ "regex",
+]
+
+[[package]]
+name = "predicates-core"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b794032607612e7abeb4db69adb4e33590fa6cf1149e95fd7cb00e634b92f174"
+
+[[package]]
+name = "predicates-tree"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368ba315fb8c5052ab692e68a0eefec6ec57b23a36959c14496f0b0df2c0cecf"
+dependencies = [
+ "predicates-core",
+ "termtree",
+]
+
 [[package]]
 name = "prettydiff"
 version = "0.6.4"
@@ -9195,6 +9287,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "termtree"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3369f5ac52d5eb6ab48c6b4ffdc8efbcad6b89c765749064ba298f2c68a16a76"
+
 [[package]]
 name = "tests-integration"
 version = "0.4.4"
diff --git a/Cargo.toml b/Cargo.toml
index a25d4f20ce..04774aef41 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -74,6 +74,7 @@ async-trait = "0.1"
 base64 = "0.21"
 bigdecimal = "0.4.2"
 bitflags = "2.4.1"
+bytemuck = "1.12"
 chrono = { version = "0.4", features = ["serde"] }
 datafusion = { git = "https://github.com/apache/arrow-datafusion.git", rev = "26e43acac3a96cec8dd4c8365f22dfb1a84306e9" }
 datafusion-common = { git = "https://github.com/apache/arrow-datafusion.git", rev = "26e43acac3a96cec8dd4c8365f22dfb1a84306e9" }
@@ -92,6 +93,7 @@ humantime-serde = "1.1"
 itertools = "0.10"
 lazy_static = "1.4"
 meter-core = { git = "https://github.com/GreptimeTeam/greptime-meter.git", rev = "abbd357c1e193cd270ea65ee7652334a150b628f" }
+mockall = "0.11.4"
 moka = "0.12"
 once_cell = "1.18"
 opentelemetry-proto = { git = "https://github.com/waynexia/opentelemetry-rust.git", rev = "33841b38dda79b15f2024952be5f32533325ca02", features = [
diff --git a/src/index/Cargo.toml b/src/index/Cargo.toml
index 54b8c75f7e..800420164a 100644
--- a/src/index/Cargo.toml
+++ b/src/index/Cargo.toml
@@ -6,12 +6,14 @@ license.workspace = true
 
 [dependencies]
 async-trait.workspace = true
+bytemuck.workspace = true
 common-base.workspace = true
 common-error.workspace = true
 common-macro.workspace = true
 fst.workspace = true
 futures.workspace = true
 greptime-proto.workspace = true
+mockall.workspace = true
 prost.workspace = true
 regex-automata.workspace = true
 regex.workspace = true
diff --git a/src/index/src/inverted_index/format/reader.rs b/src/index/src/inverted_index/format/reader.rs
index c18c6bd83e..e8e9c72c95 100644
--- a/src/index/src/inverted_index/format/reader.rs
+++ b/src/index/src/inverted_index/format/reader.rs
@@ -23,6 +23,7 @@ use crate::inverted_index::error::Result;
 use crate::inverted_index::FstMap;
 
 /// InvertedIndexReader defines an asynchronous reader of inverted index data
+#[mockall::automock]
 #[async_trait]
 pub trait InvertedIndexReader {
     /// Retrieve metadata of all inverted indices stored within the blob.
diff --git a/src/index/src/inverted_index/search.rs b/src/index/src/inverted_index/search.rs
index d4f4b71f05..e4ab3d5c3b 100644
--- a/src/index/src/inverted_index/search.rs
+++ b/src/index/src/inverted_index/search.rs
@@ -13,4 +13,5 @@
 // limitations under the License.
 
 pub mod fst_apply;
+pub mod fst_values_mapper;
 pub mod predicate;
diff --git a/src/index/src/inverted_index/search/fst_apply/keys_apply.rs b/src/index/src/inverted_index/search/fst_apply/keys_apply.rs
index 23503a97b1..a5ed84dce7 100644
--- a/src/index/src/inverted_index/search/fst_apply/keys_apply.rs
+++ b/src/index/src/inverted_index/search/fst_apply/keys_apply.rs
@@ -283,7 +283,10 @@ mod tests {
             },
         })];
         let result = KeysFstApplier::try_from(predicates);
-        assert!(result.is_err());
+        assert!(matches!(
+            result,
+            Err(Error::KeysApplierWithoutInList { .. })
+        ));
     }
 
     #[test]
diff --git a/src/index/src/inverted_index/search/fst_values_mapper.rs b/src/index/src/inverted_index/search/fst_values_mapper.rs
new file mode 100644
index 0000000000..d4675e652d
--- /dev/null
+++ b/src/index/src/inverted_index/search/fst_values_mapper.rs
@@ -0,0 +1,112 @@
+// Copyright 2023 Greptime Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use common_base::BitVec;
+use greptime_proto::v1::index::InvertedIndexMeta;
+
+use crate::inverted_index::error::Result;
+use crate::inverted_index::format::reader::InvertedIndexReader;
+
+/// `FstValuesMapper` maps FST-encoded u64 values to their corresponding bitmaps
+/// within an inverted index. The higher 32 bits of each u64 value represent the
+/// bitmap offset and the lower 32 bits represent its size. This mapper uses these
+/// combined offset-size pairs to fetch and union multiple bitmaps into a single `BitVec`.
+pub struct FstValuesMapper<'a> {
+    /// `reader` retrieves bitmap data using offsets and sizes from FST values.
+    reader: &'a mut dyn InvertedIndexReader,
+
+    /// `metadata` provides context for interpreting the index structures.
+    metadata: &'a InvertedIndexMeta,
+}
+
+impl<'a> FstValuesMapper<'a> {
+    pub fn new(
+        reader: &'a mut dyn InvertedIndexReader,
+        metadata: &'a InvertedIndexMeta,
+    ) -> FstValuesMapper<'a> {
+        FstValuesMapper { reader, metadata }
+    }
+
+    /// Maps an array of FST values to a `BitVec` by retrieving and combining bitmaps.
+    pub async fn map_values(&mut self, values: &[u64]) -> Result<BitVec> {
+        let mut bitmap = BitVec::new();
+
+        for value in values {
+            // relative_offset (higher 32 bits), size (lower 32 bits)
+            let [relative_offset, size] = bytemuck::cast::<u64, [u32; 2]>(*value);
+
+            let bm = self
+                .reader
+                .bitmap(self.metadata, relative_offset, size)
+                .await?;
+
+            // Ensure the longest BitVec is the left operand to prevent truncation during OR.
+            if bm.len() > bitmap.len() {
+                bitmap = bm | bitmap
+            } else {
+                bitmap |= bm
+            }
+        }
+
+        Ok(bitmap)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use common_base::bit_vec::prelude::*;
+
+    use super::*;
+    use crate::inverted_index::format::reader::MockInvertedIndexReader;
+
+    fn value(offset: u32, size: u32) -> u64 {
+        bytemuck::cast::<[u32; 2], u64>([offset, size])
+    }
+
+    #[tokio::test]
+    async fn test_map_values() {
+        let mut mock_reader = MockInvertedIndexReader::new();
+        mock_reader
+            .expect_bitmap()
+            .returning(|_, offset, size| match (offset, size) {
+                (1, 1) => Ok(bitvec![u8, Lsb0; 1, 0, 1, 0, 1, 0, 1]),
+                (2, 1) => Ok(bitvec![u8, Lsb0; 0, 1, 0, 1, 0, 1, 0, 1]),
+                _ => unreachable!(),
+            });
+
+        let meta = InvertedIndexMeta::default();
+        let mut values_mapper = FstValuesMapper::new(&mut mock_reader, &meta);
+
+        let result = values_mapper.map_values(&[]).await.unwrap();
+        assert_eq!(result.count_ones(), 0);
+
+        let result = values_mapper.map_values(&[value(1, 1)]).await.unwrap();
+        assert_eq!(result, bitvec![u8, Lsb0; 1, 0, 1, 0, 1, 0, 1]);
+
+        let result = values_mapper.map_values(&[value(2, 1)]).await.unwrap();
+        assert_eq!(result, bitvec![u8, Lsb0; 0, 1, 0, 1, 0, 1, 0, 1]);
+
+        let result = values_mapper
+            .map_values(&[value(1, 1), value(2, 1)])
+            .await
+            .unwrap();
+        assert_eq!(result, bitvec![u8, Lsb0; 1, 1, 1, 1, 1, 1, 1, 1]);
+
+        let result = values_mapper
+            .map_values(&[value(2, 1), value(1, 1)])
+            .await
+            .unwrap();
+        assert_eq!(result, bitvec![u8, Lsb0; 1, 1, 1, 1, 1, 1, 1, 1]);
+    }
+}
diff --git a/src/promql/Cargo.toml b/src/promql/Cargo.toml
index fb4984b6e0..a10973d4eb 100644
--- a/src/promql/Cargo.toml
+++ b/src/promql/Cargo.toml
@@ -7,7 +7,7 @@ license.workspace = true
 [dependencies]
 async-recursion = "1.0"
 async-trait.workspace = true
-bytemuck = "1.12"
+bytemuck.workspace = true
 catalog.workspace = true
 common-catalog.workspace = true
 common-error.workspace = true