diff --git a/paimon-common/src/main/java/org/apache/paimon/fs/cache/FileSizeMemo.java b/paimon-common/src/main/java/org/apache/paimon/fs/cache/FileSizeMemo.java
new file mode 100644
index 000000000000..5691596d3624
--- /dev/null
+++ b/paimon-common/src/main/java/org/apache/paimon/fs/cache/FileSizeMemo.java
@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.paimon.fs.cache;
+
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+
+/**
+ * Least-recently-used memo of file sizes, bounded by entry count.
+ *
+ * <p>A memo is tiny but there is one per path, so an unbounded map grows with the number of
+ * distinct files a long-lived process reads. Losing one only costs the extra {@code getFileStatus}
+ * that would have been made anyway, and the files these caches accept are immutable, so a re-read
+ * returns the same size.
+ *
+ * <p>Not thread-safe: callers hold their own lock. Access order means {@link #get} mutates the map,
+ * so even a read has to be inside it.
+ */
+class FileSizeMemo {
+
+    private static final int MAX_ENTRIES = 65536;
+
+    private final LinkedHashMap<String, Long> sizes = new LinkedHashMap<>(64, 0.75f, true);
+
+    /** Read through a method, not the constant: a constant is inlined into the test's bytecode. */
+    static int maxEntries() {
+        return MAX_ENTRIES;
+    }
+
+    /** Entry count, so a test can observe the bound without reading an entry. */
+    int size() {
+        return sizes.size();
+    }
+
+    long get(String filePath) {
+        Long size = sizes.get(filePath);
+        return size != null ? size : -1;
+    }
+
+    void put(String filePath, long size) {
+        sizes.put(filePath, size);
+        Iterator<String> iterator = sizes.keySet().iterator();
+        while (sizes.size() > MAX_ENTRIES && iterator.hasNext()) {
+            iterator.next();
+            iterator.remove();
+        }
+    }
+
+    void invalidate(String filePathPrefix) {
+        sizes.keySet().removeIf(filePath -> filePath.startsWith(filePathPrefix));
+    }
+}
diff --git a/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalDiskCacheManager.java b/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalDiskCacheManager.java
index d020feac427e..4f05b9415fc1 100644
--- a/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalDiskCacheManager.java
+++ b/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalDiskCacheManager.java
@@ -38,7 +38,6 @@
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
 
 /** Block-level local disk cache with LRU eviction. Thread-safe. */
 public class LocalDiskCacheManager implements LocalCacheManager {
@@ -50,7 +49,7 @@ public class LocalDiskCacheManager implements LocalCacheManager {
     private final long maxSizeBytes;
     private final int blockSize;
     private final Object lock = new Object();
-    private final ConcurrentHashMap<String, Long> fileSizeCache = new ConcurrentHashMap<>();
+    private final FileSizeMemo fileSizeMemo = new FileSizeMemo();
 
     // LRU-ordered index: key -> size. Access order so get() moves entry to tail.
     private final LinkedHashMap<String, Long> entryIndex;
@@ -240,12 +239,15 @@ long currentSize() {
 
     @Override
     public long getFileSize(String filePath) {
-        Long size = fileSizeCache.get(filePath);
-        return size != null ? size : -1;
+        synchronized (lock) {
+            return fileSizeMemo.get(filePath);
+        }
     }
 
     @Override
     public void putFileSize(String filePath, long size) {
-        fileSizeCache.put(filePath, size);
+        synchronized (lock) {
+            fileSizeMemo.put(filePath, size);
+        }
     }
 }
diff --git a/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalMemoryCacheManager.java b/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalMemoryCacheManager.java
index e92cb88412fe..541940e668dc 100644
--- a/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalMemoryCacheManager.java
+++ b/paimon-common/src/main/java/org/apache/paimon/fs/cache/LocalMemoryCacheManager.java
@@ -24,16 +24,18 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
-import java.util.concurrent.ConcurrentHashMap;
 
-/** Block-level in-memory cache with LRU eviction. Thread-safe. */
+/**
+ * In-memory cache with LRU eviction, holding data blocks bounded by total bytes and a {@link
+ * FileSizeMemo} bounded by entry count. Thread-safe.
+ */
 public class LocalMemoryCacheManager implements LocalCacheManager {
 
     private final long maxSizeBytes;
     private final int blockSize;
     private final Object lock = new Object();
     private final LinkedHashMap<BlockKey, byte[]> cache;
-    private final ConcurrentHashMap<String, Long> fileSizeCache = new ConcurrentHashMap<>();
+    private final FileSizeMemo fileSizeMemo = new FileSizeMemo();
 
     private long currentSize;
 
@@ -80,13 +82,16 @@ public void putBlock(String filePath, int blockIndex, byte[] data) {
 
     @Override
     public long getFileSize(String filePath) {
-        Long size = fileSizeCache.get(filePath);
-        return size != null ? size : -1;
+        synchronized (lock) {
+            return fileSizeMemo.get(filePath);
+        }
     }
 
     @Override
     public void putFileSize(String filePath, long size) {
-        fileSizeCache.put(filePath, size);
+        synchronized (lock) {
+            fileSizeMemo.put(filePath, size);
+        }
     }
 
     @Override
@@ -100,8 +105,8 @@ public void invalidate(String filePathPrefix) {
                     iterator.remove();
                 }
             }
+            fileSizeMemo.invalidate(filePathPrefix);
         }
-        fileSizeCache.keySet().removeIf(filePath -> filePath.startsWith(filePathPrefix));
     }
 
     private static class BlockKey {
diff --git a/paimon-common/src/test/java/org/apache/paimon/fs/cache/CachingFileIOTest.java b/paimon-common/src/test/java/org/apache/paimon/fs/cache/CachingFileIOTest.java
index 05ddd7cad08f..d3ae9d06633e 100644
--- a/paimon-common/src/test/java/org/apache/paimon/fs/cache/CachingFileIOTest.java
+++ b/paimon-common/src/test/java/org/apache/paimon/fs/cache/CachingFileIOTest.java
@@ -212,6 +212,44 @@ void testShortRemoteReadIsNotCachedAsZeroPaddedBlock() throws IOException {
         }
     }
 
+    @Test
+    void fileSizeMemoIsBounded() {
+        // both cache managers keep this memo, and either one is picked purely by whether
+        // local-cache.dir is set, so the bound has to hold for both
+        assertFileSizeMemoIsBounded(new LocalMemoryCacheManager(Long.MAX_VALUE, 64));
+        assertFileSizeMemoIsBounded(
+                new LocalDiskCacheManager(
+                        tempDir.resolve("memo-bound").toString(), Long.MAX_VALUE, 64));
+    }
+
+    private static void assertFileSizeMemoIsBounded(LocalCacheManager cache) {
+        // more puts than the bound, so eviction has to run. FileSizeMemoTest pins the count and
+        // the eviction order; this only checks that the manager routes through a bounded memo.
+        long entries = FileSizeMemo.maxEntries() + 1024L;
+
+        cache.putFileSize("file-0", 100L);
+        for (long i = 1; i <= entries; i++) {
+            cache.putFileSize("file-" + i, i);
+        }
+
+        assertThat(cache.getFileSize("file-0")).isEqualTo(-1L);
+        assertThat(cache.getFileSize("file-" + entries)).isEqualTo(entries);
+    }
+
+    @Test
+    void memoryCacheInvalidatesFileSizeMemoByPrefix() {
+        // only the memory manager overrides invalidate; the disk one inherits the no-op default,
+        // which this PR does not change
+        LocalMemoryCacheManager cache = new LocalMemoryCacheManager(Long.MAX_VALUE, 64);
+        cache.putFileSize("ns/a", 1L);
+        cache.putFileSize("other/a", 2L);
+
+        cache.invalidate("ns/");
+
+        assertThat(cache.getFileSize("ns/a")).isEqualTo(-1L);
+        assertThat(cache.getFileSize("other/a")).isEqualTo(2L);
+    }
+
     @Test
     void testMetaFileIsCached() throws IOException {
         byte[] data = "snapshot data".getBytes();
diff --git a/paimon-common/src/test/java/org/apache/paimon/fs/cache/FileSizeMemoTest.java b/paimon-common/src/test/java/org/apache/paimon/fs/cache/FileSizeMemoTest.java
new file mode 100644
index 000000000000..d7f9326494d9
--- /dev/null
+++ b/paimon-common/src/test/java/org/apache/paimon/fs/cache/FileSizeMemoTest.java
@@ -0,0 +1,115 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.paimon.fs.cache;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/** Tests for {@link FileSizeMemo}. */
+class FileSizeMemoTest {
+
+    @Test
+    void putsAloneBoundTheMemo() {
+        int bound = FileSizeMemo.maxEntries();
+        FileSizeMemo memo = new FileSizeMemo();
+
+        for (int i = 0; i < bound; i++) {
+            memo.put("file-" + i, i);
+        }
+        assertThat(memo.size()).isEqualTo(bound);
+
+        // check the first overflow on its own: a step that evicts the wrong number of entries
+        // shows up here, where no later put can bring the count back to the bound
+        memo.put("over-0", 0L);
+        assertThat(memo.size()).isEqualTo(bound);
+
+        for (int i = 1; i < 1024; i++) {
+            memo.put("over-" + i, i);
+        }
+        // no read anywhere above, so the write path is what has to bound it
+        assertThat(memo.size()).isEqualTo(bound);
+    }
+
+    @Test
+    void aReadEntryOutlivesAnUnreadOne() {
+        int bound = FileSizeMemo.maxEntries();
+        // below 4 the four assertions below are not four distinct keys
+        assertThat(bound).isGreaterThanOrEqualTo(4);
+        int read = bound / 2;
+        int unread = bound - read;
+        FileSizeMemo memo = new FileSizeMemo();
+        for (int i = 0; i < bound; i++) {
+            memo.put("file-" + i, i);
+        }
+
+        // reading the older entries makes them the recently used ones
+        for (int i = 0; i < read; i++) {
+            assertThat(memo.get("file-" + i)).isEqualTo(i);
+        }
+        // exactly as many new entries as were left unread, so those are what eviction takes
+        for (int i = bound; i < bound + unread; i++) {
+            memo.put("file-" + i, i);
+        }
+
+        assertThat(memo.get("file-0")).isEqualTo(0L);
+        assertThat(memo.get("file-" + (read - 1))).isEqualTo(read - 1L);
+        assertThat(memo.get("file-" + read)).isEqualTo(-1L);
+        assertThat(memo.get("file-" + (bound - 1))).isEqualTo(-1L);
+    }
+
+    @Test
+    void puttingAnEntryAgainRefreshesIt() {
+        int bound = FileSizeMemo.maxEntries();
+        // at a bound of 1 the loop below never runs, so nothing would pin the position half
+        assertThat(bound).isGreaterThanOrEqualTo(2);
+        FileSizeMemo memo = new FileSizeMemo();
+        for (int i = 0; i < bound; i++) {
+            memo.put("file-" + i, i);
+        }
+
+        memo.put("file-0", 100L);
+        for (int i = bound; i < bound + bound - 1; i++) {
+            memo.put("file-" + i, i);
+        }
+
+        // the re-put carried both the newer value and the newer position
+        assertThat(memo.get("file-0")).isEqualTo(100L);
+        assertThat(memo.get("file-1")).isEqualTo(-1L);
+    }
+
+    @Test
+    void invalidateRemovesOnlyTheMatchingPrefix() {
+        // the fixture below holds four entries, and none of them may be evicted
+        assertThat(FileSizeMemo.maxEntries()).isGreaterThanOrEqualTo(4);
+        FileSizeMemo memo = new FileSizeMemo();
+        memo.put("/a/one", 1L);
+        memo.put("/a/two", 2L);
+        memo.put("/b/three", 3L);
+        // carries the prefix, but not at the front
+        memo.put("/b/a/four", 4L);
+
+        memo.invalidate("/a/");
+
+        assertThat(memo.get("/a/one")).isEqualTo(-1L);
+        assertThat(memo.get("/a/two")).isEqualTo(-1L);
+        assertThat(memo.get("/b/three")).isEqualTo(3L);
+        assertThat(memo.get("/b/a/four")).isEqualTo(4L);
+    }
+}