perf: cache alias mapping

CHANGES.rst

@@ -23,7 +23,7 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- Performance improvement for combining data files.
 
 
 .. scriv-start-here

coverage/control.py

@@ -998,7 +998,7 @@ def _prepare_data_for_reporting(self) -> None:
         if self.config.paths:
             mapped_data = CoverageData(warn=self._warn, debug=self._debug, no_disk=True)
             if self._data is not None:
-                mapped_data.update(self._data, aliases=self._make_aliases())
+                mapped_data.update(self._data, map_path=self._make_aliases().map)
             self._data = mapped_data
 
     def report(

coverage/data.py

@@ -12,6 +12,7 @@
 
 from __future__ import annotations
 
+import functools
 import glob
 import hashlib
 import os.path
@@ -134,6 +135,11 @@ def combine_parallel_data(
     if strict and not files_to_combine:
         raise NoDataError("No data to combine")
 
+    if aliases is None:
+        map_path = None
+    else:
+        map_path = functools.lru_cache(maxsize=None)(aliases.map)
+
     file_hashes = set()
     combined_any = False
 
@@ -176,7 +182,7 @@ def combine_parallel_data(
                     message(f"Couldn't combine data file {rel_file_name}: {exc}")
                 delete_this_one = False
             else:
-                data.update(new_data, aliases=aliases)
+                data.update(new_data, map_path=map_path)
                 combined_any = True
                 if message:
                     message(f"Combined data file {rel_file_name}")

coverage/sqldata.py

@@ -21,13 +21,12 @@
 import zlib
 
 from typing import (
-    cast, Any, Collection, Mapping,
+    cast, Any, Callable, Collection, Mapping,
     Sequence,
 )
 
 from coverage.debug import NoDebugging, auto_repr
 from coverage.exceptions import CoverageException, DataError
-from coverage.files import PathAliases
 from coverage.misc import file_be_gone, isolate_module
 from coverage.numbits import numbits_to_nums, numbits_union, nums_to_numbits
 from coverage.sqlitedb import SqliteDb
@@ -647,12 +646,16 @@ def purge_files(self, filenames: Collection[str]) -> None:
                     continue
                 con.execute_void(sql, (file_id,))
 
-    def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -> None:
-        """Update this data with data from several other :class:`CoverageData` instances.
+    def update(
+        self,
+        other_data: CoverageData,
+        map_path: Callable[[str], str] | None = None,
+    ) -> None:
+        """Update this data with data from another :class:`CoverageData`.
 
-        If `aliases` is provided, it's a `PathAliases` object that is used to
-        re-map paths to match the local machine's.  Note: `aliases` is None
-        only when called directly from the test suite.
+        If `map_path` is provided, it's a function that re-map paths to match
+        the local machine's.  Note: `map_path` is None only when called
+        directly from the test suite.
 
         """
         if self._debug.should("dataop"):
@@ -664,7 +667,7 @@ def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -
         if self._has_arcs and other_data._has_lines:
             raise DataError("Can't combine line data with arc data")
 
-        aliases = aliases or PathAliases()
+        map_path = map_path or (lambda p: p)
 
         # Force the database we're writing to to exist before we start nesting contexts.
         self._start_using()
@@ -674,7 +677,7 @@ def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -
         with other_data._connect() as con:
             # Get files data.
             with con.execute("select path from file") as cur:
-                files = {path: aliases.map(path) for (path,) in cur}
+                files = {path: map_path(path) for (path,) in cur}
 
             # Get contexts data.
             with con.execute("select context from context") as cur:
@@ -729,7 +732,7 @@ def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -
                 "inner join file on file.id = tracer.file_id",
             ) as cur:
                 this_tracers.update({
-                    aliases.map(path): tracer
+                    map_path(path): tracer
                     for path, tracer in cur
                 })
 
@@ -768,7 +771,21 @@ def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -
             # and context strings with integer ids. Then use the efficient
             # `executemany()` to insert all rows at once.
 
-            # Get line data.
+            if arcs:
+                self._choose_lines_or_arcs(arcs=True)
+
+                arc_rows = (
+                    (file_ids[file], context_ids[context], fromno, tono)
+                    for file, context, fromno, tono in arcs
+                )
+
+                # Write the combined data.
+                con.executemany_void(
+                    "insert or ignore into arc " +
+                    "(file_id, context_id, fromno, tono) values (?, ?, ?, ?)",
+                    arc_rows,
+                )
+
             if lines:
                 self._choose_lines_or_arcs(lines=True)
 
@@ -779,7 +796,7 @@ def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -
                     "inner join context on context.id = line_bits.context_id",
                 ) as cur:
                     for path, context, numbits in cur:
-                        key = (aliases.map(path), context)
+                        key = (aliases_map(path), context)
                         if key in lines:
                             lines[key] = numbits_union(lines[key], numbits)
 
@@ -792,21 +809,6 @@ def update(self, other_data: CoverageData, aliases: PathAliases | None = None) -
                     ],
                 )
 
-            if arcs:
-                self._choose_lines_or_arcs(arcs=True)
-
-                arc_rows = (
-                    (file_ids[file], context_ids[context], fromno, tono)
-                    for file, context, fromno, tono in arcs
-                )
-
-                # Write the combined data.
-                con.executemany_void(
-                    "insert or ignore into arc " +
-                    "(file_id, context_id, fromno, tono) values (?, ?, ?, ?)",
-                    arc_rows,
-                )
-
             con.executemany_void(
                 "insert or ignore into tracer (file_id, tracer) values (?, ?)",
                 ((file_ids[filename], tracer) for filename, tracer in tracer_map.items()),