fix(python): expose optimize compaction options (#3870)

## Summary
- expose typed compaction options on synchronous and asynchronous table
optimization
- translate validated Python options into native Lance compaction
settings
- document the row-based steady-state limit and first-pass/source-budget
caveats
- carry the Lance beta.15 fragment-exclusion option through the typed
Python API

## Root cause
The native Python optimize binding always constructed default compaction
settings, and the public AsyncTable API offered no way to lower the
fragment row target. Wide-row fragments therefore remained compaction
candidates on every later optimize call, repeatedly rewriting the
accumulated table.

## Limitations
This is an explicit row-based mitigation, not byte-native task sizing or
a hard memory cap. Callers must derive target_rows_per_fragment from
expected row size. Existing oversized fragments are rewritten whole on
the first pass; max_bytes_per_file limits output file size rather than
compaction memory; and source budgets admit whole planned tasks, so a
budget below the first task performs no compaction. Splitting tasks by a
byte budget or returning a planner error requires a Lance-side change.

## Validation
- cargo check --release -p lancedb-python
- cargo clippy --quiet -p lancedb-python
- cargo fmt --all --check
- ruff format --check python tests
- ruff check python tests
- uv run --no-sync pytest python/tests/test_table.py -k
optimize_compaction -q (16 passed)

Fixes #2325

<!-- lance-gatekeeper-fix:v1 agent=9b58eee0c79040b19540e259af0e676c
generation=1 -->

---------

Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>
Co-authored-by: Xuanwo <github@xuanwo.io>

python/python/lancedb/__init__.py

@@ -49,7 +49,7 @@ from .materialized_view import (
     MaterializedViewDefinition,
 )
 from .view import ViewDescription as ViewDescription
-from .table import AsyncTable, Table
+from .table import AsyncTable, CompactionOptions, Table
 from .types import BaseTokenizerType
 from ._lancedb import Session
 from .namespace import (
@@ -610,6 +610,7 @@ __all__ = [
     "AsyncSqlQuery",
     "AsyncLanceNamespaceDBConnection",
     "AsyncTable",
+    "CompactionOptions",
     "FtsToken",
     "col",
     "Expr",

python/python/lancedb/_lancedb.pyi

@@ -544,6 +544,7 @@ class Table:
         *,
         cleanup_since_ms: Optional[int] = None,
         delete_unverified: Optional[bool] = None,
+        compaction_options: Optional[Dict[str, Any]] = None,
     ) -> OptimizeStats: ...
     async def uri(self) -> str: ...
     async def initial_storage_options(self) -> Optional[Dict[str, str]]: ...

python/python/lancedb/remote/table.py

@@ -67,6 +67,7 @@ from ..table import (
     AsyncTable,
     BlobMode,
     Branches,
+    CompactionOptions,
     IndexStatistics,
     Query,
     Table,
@@ -1071,6 +1072,7 @@ class RemoteTable(Table):
         cleanup_older_than: Optional[timedelta] = None,
         delete_unverified: bool = False,
         retrain: bool = False,
+        compaction_options: Optional[CompactionOptions] = None,
     ):
         """optimize() is not supported for remote tables."""
         return LOOP.run(

python/python/lancedb/table.py

@@ -25,6 +25,7 @@ from typing import (
     Optional,
     Sequence,
     Tuple,
+    TypedDict,
     Union,
     overload,
 )
@@ -285,6 +286,91 @@ IndexConfigType = Union[
     FTS,
 ]
 
+
+class CompactionOptions(TypedDict, total=False):
+    """Options that control file compaction during table optimization.
+
+    Unspecified options use Lance's defaults.
+
+    Compaction planning is row based. Lowering ``target_rows_per_fragment``
+    based on the expected row size can bound later compaction passes once
+    oversized fragments have been rewritten. It does not split an existing
+    fragment, so the first pass over an oversized fragment is not subject to
+    that bound. ``max_bytes_per_file`` limits output file size, not compaction
+    memory. Source budgets keep whole planned tasks; if the first task exceeds
+    a budget, that run performs no compaction work.
+
+    Examples
+    --------
+    Derive a steady-state row target from the expected row size:
+
+    >>> desired_fragment_bytes = 750 * 1024 * 1024
+    >>> average_row_bytes = 1_500_000
+    >>> options: CompactionOptions = {
+    ...     "target_rows_per_fragment": max(
+    ...         1, desired_fragment_bytes // average_row_bytes
+    ...     ),
+    ... }
+    >>> await table.optimize(compaction_options=options)  # doctest: +SKIP
+    """
+
+    target_rows_per_fragment: int
+    """Target rows per fragment; existing oversized fragments are not split."""
+
+    max_rows_per_group: int
+    """Maximum number of rows per row group (default: 1,024)."""
+
+    max_bytes_per_file: Optional[int]
+    """Maximum output data-file size; this does not bound compaction memory."""
+
+    materialize_deletions: bool
+    """Whether to rewrite fragments containing deleted rows (default: True)."""
+
+    materialize_deletions_threshold: float
+    """Minimum deleted-row fraction that makes a fragment eligible (default: 0.1)."""
+
+    num_threads: Optional[int]
+    """Number of compaction tasks to run in parallel."""
+
+    batch_size: Optional[int]
+    """Number of rows per input scan batch."""
+
+    io_buffer_size: Optional[int]
+    """Maximum number of bytes queued in the input scan I/O buffer."""
+
+    defer_index_remap: bool
+    """Whether to defer index remapping during compaction (default: False)."""
+
+    index_remap_mode: Literal["direct", "compact"]
+    """How to construct the old-to-new row-address mapping."""
+
+    compaction_mode: Optional[
+        Literal["reencode", "try_binary_copy", "force_binary_copy"]
+    ]
+    """Whether compaction re-encodes data or uses binary copying."""
+
+    binary_copy_read_batch_bytes: Optional[int]
+    """Number of bytes read per batch during binary-copy compaction."""
+
+    max_source_fragments: Optional[int]
+    """Maximum number of source fragments compacted in one run."""
+
+    max_source_rows: Optional[int]
+    """Maximum live source rows per run, applied to whole planned tasks."""
+
+    max_source_bytes: Optional[int]
+    """Maximum source bytes per run, applied to whole planned tasks."""
+
+    excluded_fragment_ids: List[int]
+    """Fragment IDs to leave unchanged and use as planning boundaries."""
+
+    max_overlays_per_fragment: Optional[int]
+    """Maximum overlays before a fragment is fully compacted."""
+
+    data_storage_version: str
+    """Data-file version or release selector for compacted output."""
+
+
 # Known distance metrics for legacy API detection
 KNOWN_METRICS = {"l2", "cosine", "dot", "hamming"}
 
@@ -2767,6 +2853,7 @@ class Table(ABC):
         cleanup_older_than: Optional[timedelta] = None,
         delete_unverified: bool = False,
         retrain: bool = False,
+        compaction_options: Optional[CompactionOptions] = None,
     ):
         """
         Optimize the on-disk data and indices for better performance.
@@ -2806,6 +2893,11 @@ class Table(ABC):
 
         retrain: bool, default False
             This parameter is no longer used and is deprecated.
+        compaction_options: CompactionOptions, optional
+            Options that control file compaction. For large rows, derive a lower
+            ``target_rows_per_fragment`` from the expected row size to bound later
+            passes. This does not cap the first pass over an existing oversized
+            fragment; see [CompactionOptions][lancedb.table.CompactionOptions].
 
         Notes
         -----
@@ -4893,6 +4985,7 @@ class LanceTable(Table):
         cleanup_older_than: Optional[timedelta] = None,
         delete_unverified: bool = False,
         retrain: bool = False,
+        compaction_options: Optional[CompactionOptions] = None,
     ):
         """
         Optimize the on-disk data and indices for better performance.
@@ -4932,6 +5025,11 @@ class LanceTable(Table):
 
         retrain: bool, default False
             This parameter is no longer used and is deprecated.
+        compaction_options: CompactionOptions, optional
+            Options that control file compaction. For large rows, derive a lower
+            ``target_rows_per_fragment`` from the expected row size to bound later
+            passes. This does not cap the first pass over an existing oversized
+            fragment; see [CompactionOptions][lancedb.table.CompactionOptions].
 
         Notes
         -----
@@ -4945,6 +5043,7 @@ class LanceTable(Table):
             self._table._do_optimize(
                 _optimize_cleanup_since_ms(cleanup_older_than, retrain),
                 delete_unverified,
+                compaction_options,
             )
         )
 
@@ -7620,6 +7719,7 @@ class AsyncTable:
         cleanup_older_than: Optional[timedelta] = None,
         delete_unverified: bool = False,
         retrain=False,
+        compaction_options: Optional[CompactionOptions] = None,
     ) -> OptimizeStats:
         """
         Optimize the on-disk data and indices for better performance.
@@ -7659,6 +7759,11 @@ class AsyncTable:
 
         retrain: bool, default False
             This parameter is no longer used and is deprecated.
+        compaction_options: CompactionOptions, optional
+            Options that control file compaction. For large rows, derive a lower
+            ``target_rows_per_fragment`` from the expected row size to bound later
+            passes. This does not cap the first pass over an existing oversized
+            fragment; see [CompactionOptions][lancedb.table.CompactionOptions].
 
         Notes
         -----
@@ -7671,14 +7776,19 @@ class AsyncTable:
         return await self._do_optimize(
             _optimize_cleanup_since_ms(cleanup_older_than, retrain),
             delete_unverified,
+            compaction_options,
         )
 
     async def _do_optimize(
-        self, cleanup_since_ms: Optional[int], delete_unverified: bool
+        self,
+        cleanup_since_ms: Optional[int],
+        delete_unverified: bool,
+        compaction_options: Optional[CompactionOptions] = None,
     ) -> OptimizeStats:
         return await self._inner.optimize(
             cleanup_since_ms=cleanup_since_ms,
             delete_unverified=delete_unverified,
+            compaction_options=compaction_options,
         )
 
     async def list_indices(self) -> Iterable[IndexConfig]:

python/python/tests/test_table.py

@@ -14,7 +14,7 @@ from concurrent.futures import ThreadPoolExecutor
 from datetime import date, datetime, timedelta
 from decimal import Decimal, localcontext
 from time import sleep
-from typing import List
+from typing import Any, List
 from unittest.mock import MagicMock, patch
 
 import lancedb
@@ -5014,6 +5014,134 @@ async def test_optimize(mem_db_async: AsyncConnection):
     assert await table.query().to_arrow() == pa.table({"x": [[1], [2]]})
 
 
+@pytest.mark.asyncio
+async def test_optimize_compaction_options(mem_db_async: AsyncConnection):
+    table = await mem_db_async.create_table("test", data=[{"x": 1}])
+    await table.add([{"x": 2}])
+
+    stats = await table.optimize(
+        compaction_options={
+            "target_rows_per_fragment": 1,
+            "batch_size": 1,
+            "num_threads": 1,
+        }
+    )
+    assert stats.compaction.fragments_removed == 0
+    assert stats.compaction.fragments_added == 0
+
+    stats = await table.optimize(compaction_options={"target_rows_per_fragment": 3})
+    assert stats.compaction.fragments_removed == 2
+    assert stats.compaction.fragments_added == 1
+
+    with pytest.raises(ValueError, match="Invalid compaction option: unknown"):
+        await table.optimize(compaction_options={"unknown": 1})
+
+
+def test_optimize_compaction_options_sync(mem_db: DBConnection):
+    table = mem_db.create_table("test", data=[{"x": 1}])
+    with pytest.raises(ValueError, match="target_rows_per_fragment must be between"):
+        table.optimize(compaction_options={"target_rows_per_fragment": 0})
+
+
+@pytest.mark.parametrize("option", ["max_source_rows", "max_source_bytes"])
+@pytest.mark.asyncio
+async def test_optimize_compaction_source_limits(
+    mem_db_async: AsyncConnection, option: str
+):
+    table = await mem_db_async.create_table("test", data=[{"x": 1}])
+    await table.add([{"x": 2}])
+
+    stats = await table.optimize(
+        compaction_options={
+            "target_rows_per_fragment": 3,
+            option: 1,
+        }
+    )
+    assert stats.compaction.fragments_removed == 0
+    assert stats.compaction.fragments_added == 0
+
+
+@pytest.mark.asyncio
+async def test_optimize_compaction_data_storage_version(
+    mem_db_async: AsyncConnection,
+):
+    table = await mem_db_async.create_table("test", data=[{"x": 1}])
+    await table.add([{"x": 2}])
+
+    stats = await table.optimize(
+        compaction_options={
+            "target_rows_per_fragment": 3,
+            "data_storage_version": "2.2",
+        }
+    )
+    assert stats.compaction.fragments_removed == 2
+    assert stats.compaction.fragments_added == 1
+
+    table = await mem_db_async.create_table("cross_family", data=[{"x": 1}])
+    await table.add([{"x": 2}])
+    with pytest.raises(ValueError, match="V1 and V2 storage versions cannot be mixed"):
+        await table.optimize(
+            compaction_options={
+                "target_rows_per_fragment": 3,
+                "data_storage_version": "legacy",
+            }
+        )
+
+
+@pytest.mark.asyncio
+async def test_optimize_compaction_excluded_fragments(mem_db_async: AsyncConnection):
+    table = await mem_db_async.create_table("test", data=[{"x": 1}])
+    await table.add([{"x": 2}])
+
+    stats = await table.optimize(
+        compaction_options={
+            "target_rows_per_fragment": 3,
+            "excluded_fragment_ids": [0],
+        }
+    )
+    assert stats.compaction.fragments_removed == 0
+    assert stats.compaction.fragments_added == 0
+
+    stats = await table.optimize(compaction_options={"target_rows_per_fragment": 3})
+    assert stats.compaction.fragments_removed == 2
+    assert stats.compaction.fragments_added == 1
+
+
+@pytest.mark.parametrize(
+    ("option", "value", "message"),
+    [
+        ("target_rows_per_fragment", 0, "must be between 1 and 4294967295"),
+        ("max_rows_per_group", 0, "must be between 1 and 4294967295"),
+        ("batch_size", 0, "must be between 1 and 4294967295"),
+        ("num_threads", 0, "must be greater than 0"),
+        ("target_rows_per_fragment", 2**32, "must be between 1 and 4294967295"),
+        ("max_rows_per_group", 2**32, "must be between 1 and 4294967295"),
+        ("batch_size", 2**32, "must be between 1 and 4294967295"),
+        ("io_buffer_size", 2**63, "must be at most 9223372036854775807"),
+        ("max_source_rows", 0, "must be greater than 0"),
+        ("max_source_bytes", 0, "must be greater than 0"),
+        ("data_storage_version", "invalid", "Unknown Lance storage version: invalid"),
+        (
+            "excluded_fragment_ids",
+            [-1],
+            "must contain values between 0 and 4294967295",
+        ),
+        (
+            "excluded_fragment_ids",
+            [2**32],
+            "must contain values between 0 and 4294967295",
+        ),
+    ],
+)
+@pytest.mark.asyncio
+async def test_optimize_compaction_options_validation(
+    mem_db_async: AsyncConnection, option: str, value: Any, message: str
+):
+    table = await mem_db_async.create_table("test", data=[{"x": 1}])
+    with pytest.raises(ValueError, match=message):
+        await table.optimize(compaction_options={option: value})
+
+
 @pytest.mark.asyncio
 async def test_optimize_delete_unverified(tmp_db_async: AsyncConnection, tmp_path):
     table = await tmp_db_async.create_table(

python/src/table.rs

@@ -25,10 +25,12 @@ use arrow::{
     pyarrow::{FromPyArrow, PyArrowType, ToPyArrow},
 };
 use lancedb::blob::{BlobDescriptor, BlobFile, BlobRangeRequest};
+use lancedb::connection::LanceFileVersion;
 use lancedb::index::scalar::FtsIndexBuilder;
 use lancedb::table::{
-    AddDataMode, ColumnAlteration, Duration, FieldMetadataUpdate, FtsToken as LanceDbFtsToken,
-    NewColumnTransform, OptimizeAction, OptimizeOptions, Ref, Table as LanceDbTable,
+    AddDataMode, ColumnAlteration, CompactionMode, CompactionOptions, Duration,
+    FieldMetadataUpdate, FtsToken as LanceDbFtsToken, IndexRemapMode, NewColumnTransform,
+    OptimizeAction, OptimizeOptions, Ref, Table as LanceDbTable,
 };
 use lancedb::tokenize as lancedb_tokenize;
 use pyo3::{
@@ -107,6 +109,136 @@ enum PredicateArg {
     Sql(String),
 }
 
+fn validate_positive_u32(value: u64, name: &str) -> PyResult<usize> {
+    if !(1..=u32::MAX as u64).contains(&value) {
+        return Err(PyValueError::new_err(format!(
+            "{name} must be between 1 and {}",
+            u32::MAX
+        )));
+    }
+    Ok(value as usize)
+}
+
+fn positive_u32(value: &Bound<'_, PyAny>, name: &str) -> PyResult<usize> {
+    validate_positive_u32(value.extract()?, name)
+}
+
+fn optional_positive_u32(value: &Bound<'_, PyAny>, name: &str) -> PyResult<Option<usize>> {
+    value
+        .extract::<Option<u64>>()?
+        .map(|value| validate_positive_u32(value, name))
+        .transpose()
+}
+
+fn optional_positive_usize(value: &Bound<'_, PyAny>, name: &str) -> PyResult<Option<usize>> {
+    let value: Option<usize> = value.extract()?;
+    if value == Some(0) {
+        return Err(PyValueError::new_err(format!(
+            "{name} must be greater than 0"
+        )));
+    }
+    Ok(value)
+}
+
+fn optional_positive_u64(value: &Bound<'_, PyAny>, name: &str) -> PyResult<Option<u64>> {
+    let value: Option<u64> = value.extract()?;
+    if value == Some(0) {
+        return Err(PyValueError::new_err(format!(
+            "{name} must be greater than 0"
+        )));
+    }
+    Ok(value)
+}
+
+fn u32_list(value: &Bound<'_, PyAny>, name: &str) -> PyResult<Vec<u32>> {
+    value
+        .extract::<Vec<i64>>()?
+        .into_iter()
+        .map(|value| {
+            u32::try_from(value).map_err(|_| {
+                PyValueError::new_err(format!(
+                    "{name} must contain values between 0 and {}",
+                    u32::MAX
+                ))
+            })
+        })
+        .collect()
+}
+
+fn optional_i64_bounded_u64(value: &Bound<'_, PyAny>, name: &str) -> PyResult<Option<u64>> {
+    let value: Option<u64> = value.extract()?;
+    if value.is_some_and(|value| value > i64::MAX as u64) {
+        return Err(PyValueError::new_err(format!(
+            "{name} must be at most {}",
+            i64::MAX
+        )));
+    }
+    Ok(value)
+}
+
+fn parse_compaction_options(options: Option<&Bound<'_, PyDict>>) -> PyResult<CompactionOptions> {
+    let mut parsed = CompactionOptions::default();
+    let Some(options) = options else {
+        return Ok(parsed);
+    };
+
+    for (key, value) in options.iter() {
+        let key: String = key.extract()?;
+        match key.as_str() {
+            "target_rows_per_fragment" => {
+                parsed.target_rows_per_fragment = positive_u32(&value, &key)?
+            }
+            "max_rows_per_group" => parsed.max_rows_per_group = positive_u32(&value, &key)?,
+            "max_bytes_per_file" => parsed.max_bytes_per_file = value.extract()?,
+            "materialize_deletions" => parsed.materialize_deletions = value.extract()?,
+            "materialize_deletions_threshold" => {
+                parsed.materialize_deletions_threshold = value.extract()?
+            }
+            "num_threads" => parsed.num_threads = optional_positive_usize(&value, &key)?,
+            "batch_size" => parsed.batch_size = optional_positive_u32(&value, &key)?,
+            "io_buffer_size" => parsed.io_buffer_size = optional_i64_bounded_u64(&value, &key)?,
+            "defer_index_remap" => parsed.defer_index_remap = value.extract()?,
+            "index_remap_mode" => {
+                let mode: String = value.extract()?;
+                parsed.index_remap_mode = IndexRemapMode::try_from(mode.as_str())
+                    .map_err(|err| PyValueError::new_err(err.to_string()))?;
+            }
+            "compaction_mode" => {
+                let mode: Option<String> = value.extract()?;
+                parsed.compaction_mode = mode
+                    .map(|mode| {
+                        CompactionMode::try_from(mode.as_str())
+                            .map_err(|err| PyValueError::new_err(err.to_string()))
+                    })
+                    .transpose()?;
+            }
+            "binary_copy_read_batch_bytes" => {
+                parsed.binary_copy_read_batch_bytes = value.extract()?
+            }
+            "max_source_fragments" => parsed.max_source_fragments = value.extract()?,
+            "max_source_rows" => parsed.max_source_rows = optional_positive_usize(&value, &key)?,
+            "max_source_bytes" => parsed.max_source_bytes = optional_positive_u64(&value, &key)?,
+            "excluded_fragment_ids" => parsed.excluded_fragment_ids = u32_list(&value, &key)?,
+            "max_overlays_per_fragment" => parsed.max_overlays_per_fragment = value.extract()?,
+            "data_storage_version" => {
+                let version: String = value.extract()?;
+                parsed.data_storage_version = Some(
+                    version
+                        .parse::<LanceFileVersion>()
+                        .map_err(|err| PyValueError::new_err(err.to_string()))?,
+                );
+            }
+            _ => {
+                return Err(PyValueError::new_err(format!(
+                    "Invalid compaction option: {key}"
+                )));
+            }
+        }
+    }
+
+    Ok(parsed)
+}
+
 /// Statistics about a compaction operation.
 #[pyclass(get_all, from_py_object)]
 #[derive(Clone, Debug)]
@@ -1569,13 +1701,15 @@ impl Table {
     }
 
     /// Optimize the on-disk data by compacting and pruning old data, for better performance.
-    #[pyo3(signature = (cleanup_since_ms=None, delete_unverified=None))]
-    pub fn optimize(
-        self_: PyRef<'_, Self>,
+    #[pyo3(signature = (cleanup_since_ms=None, delete_unverified=None, compaction_options=None))]
+    pub fn optimize<'py>(
+        self_: PyRef<'py, Self>,
         cleanup_since_ms: Option<u64>,
         delete_unverified: Option<bool>,
-    ) -> PyResult<Bound<'_, PyAny>> {
+        compaction_options: Option<&Bound<'py, PyDict>>,
+    ) -> PyResult<Bound<'py, PyAny>> {
         let inner = self_.inner_ref()?.clone();
+        let compaction_options = parse_compaction_options(compaction_options)?;
         let older_than = if let Some(ms) = cleanup_since_ms {
             if ms > i64::MAX as u64 {
                 return Err(PyValueError::new_err(format!(
@@ -1591,7 +1725,7 @@ impl Table {
         future_into_py(self_.py(), async move {
             let compaction_stats = inner
                 .optimize(OptimizeAction::Compact {
-                    options: lancedb::table::CompactionOptions::default(),
+                    options: compaction_options,
                     remap_options: None,
                 })
                 .await