diff --git a/backend/src/ref_backend/api/routes/diagnostics.py b/backend/src/ref_backend/api/routes/diagnostics.py
index b5ede0a3..d2abc33f 100644
--- a/backend/src/ref_backend/api/routes/diagnostics.py
+++ b/backend/src/ref_backend/api/routes/diagnostics.py
@@ -1,7 +1,7 @@
 from typing import Literal, NamedTuple
 
 from fastapi import APIRouter, HTTPException, Query, Request
-from sqlalchemy.orm import joinedload, selectinload
+from sqlalchemy.orm import joinedload
 from starlette.responses import StreamingResponse
 
 from climate_ref import models
@@ -60,15 +60,8 @@ def _get_diagnostic(
     return diagnostic
 
 
-def _listed_diagnostics(
-    app_context: AppContextDep, *, with_group_ids: bool = False
-) -> list[models.Diagnostic]:
+def _listed_diagnostics(app_context: AppContextDep) -> list[models.Diagnostic]:
     query = app_context.session.query(models.Diagnostic).options(joinedload(models.Diagnostic.provider))
-    if with_group_ids:
-        # One query for every diagnostic's group ids, rather than one per diagnostic.
-        query = query.options(
-            selectinload(models.Diagnostic.execution_groups).load_only(models.ExecutionGroup.id)
-        )
     if app_context.settings.DIAGNOSTIC_PROVIDERS:
         query = query.join(models.Provider).filter(
             models.Provider.slug.in_(app_context.settings.DIAGNOSTIC_PROVIDERS)
@@ -85,12 +78,10 @@ class _Scope(NamedTuple):
     filters: DiagnosticFilter
 
 
-def _scoped_diagnostics(
-    app_context: AppContextDep, mip_era: MipEra | None, source_id: str | None, *, with_group_ids: bool = False
-) -> _Scope:
+def _scoped_diagnostics(app_context: AppContextDep, mip_era: MipEra | None, source_id: str | None) -> _Scope:
     """Get the listed diagnostics, counting only the groups that draw on `mip_era` and ran `source_id`"""
     return _Scope(
-        _listed_diagnostics(app_context, with_group_ids=with_group_ids),
+        _listed_diagnostics(app_context),
         DiagnosticFilter(
             include_superseded=False,
             include_retracted=False,
@@ -156,7 +147,7 @@ def _list(
 
     Counts cover the promoted version of each diagnostic and leave out retracted executions.
     """
-    scope = _scoped_diagnostics(app_context, mip_era, source_id, with_group_ids=True)
+    scope = _scoped_diagnostics(app_context, mip_era, source_id)
     value_types = _value_types(app_context, scope)
     return Collection(
         data=[
@@ -182,7 +173,7 @@ def catalog(
     Checking for metric values is most of the cost of the full listing.
     Fetch those from `/diagnostics/value-flags`.
     """
-    scope = _scoped_diagnostics(app_context, mip_era, source_id, with_group_ids=True)
+    scope = _scoped_diagnostics(app_context, mip_era, source_id)
     return Collection(data=_catalog_entries(app_context, scope))
 
 
diff --git a/backend/src/ref_backend/api/routes/executions.py b/backend/src/ref_backend/api/routes/executions.py
index f570a920..df6d197c 100644
--- a/backend/src/ref_backend/api/routes/executions.py
+++ b/backend/src/ref_backend/api/routes/executions.py
@@ -1,9 +1,4 @@
 import mimetypes
-import os
-import tarfile
-import tempfile
-from collections.abc import Generator
-from pathlib import Path
 from typing import Literal, get_args
 
 from fastapi import APIRouter, HTTPException, Query, Request
@@ -18,7 +13,7 @@
 from climate_ref_core.pycmec.metric import CMECMetric
 from ref_backend.api.deps import AppContext, AppContextDep
 from ref_backend.core.execution_groups import load_execution_groups
-from ref_backend.core.file_handling import file_iterator, resolve_artifact, tail_lines
+from ref_backend.core.file_handling import file_iterator, resolve_artifact, tail_lines, tar_gz_iterator
 from ref_backend.core.metric_values import (
     MetricValueType,
     parse_id_list,
@@ -83,7 +78,7 @@ def group_counts(mip_era: MipEra | None = None) -> GroupCounts:
 @router.get("/")
 def list_recent_execution_groups(  # noqa: PLR0913, PLR0917
     app_context: AppContextDep,
-    limit: int = Query(10, ge=0),
+    limit: int = Query(10, ge=0, le=1000),
     offset: int = Query(0, ge=0),
     diagnostic_name_contains: str | None = None,
     provider_name_contains: str | None = None,
@@ -243,7 +238,7 @@ def execution_logs(
         logger.warning(f"Log file not found: {file_path}")
         raise HTTPException(status_code=404, detail="Log file not found")
 
-    headers = {"Content-Disposition": f"attachment; filename=execution_result_{execution_id}.log"}
+    headers = {"Content-Disposition": f"attachment; filename=execution_result_{execution.id}.log"}
     if lines is not None:
         tail = "".join(f"{line}\n" for line in tail_lines(file_path, lines))
         return Response(tail, media_type=mime_type, headers=headers)
@@ -367,28 +362,8 @@ def execution_archive(
     if not result_path.exists():
         raise HTTPException(status_code=404, detail="Execution output not found")
 
-    # This is an arbitrary value as a placeholder
-    # No experimentation has been done to find the best chunk size
-    CHUNK_SIZE = 128 * 1024  # 128 KB chunks
-
-    def generate_archive() -> Generator[bytes]:
-        with tempfile.NamedTemporaryFile(delete=True) as temp_tar:
-            # Open the tar file in write mode with gzip compression
-            with tarfile.open(temp_tar.name, mode="w:gz") as tar:
-                for root, _, files in os.walk(result_path):
-                    for file in files:
-                        file_path = Path(root) / file
-                        arcname = str(file_path.relative_to(result_path))
-                        tar.add(file_path, arcname=arcname)
-
-            # Read and stream the tar file in chunks
-            with open(temp_tar.name, "rb") as f:
-                while chunk := f.read(CHUNK_SIZE):
-                    yield chunk
-        # The temp file will be deleted automatically when closed
-
     return StreamingResponse(
-        generate_archive(),
+        tar_gz_iterator(result_path),
         media_type="application/x-gzip",
         headers={"Content-Disposition": f"attachment; filename=execution_{execution.id}.tar.gz"},
     )
diff --git a/backend/src/ref_backend/core/file_handling.py b/backend/src/ref_backend/core/file_handling.py
index f6547b4c..ba482b16 100644
--- a/backend/src/ref_backend/core/file_handling.py
+++ b/backend/src/ref_backend/core/file_handling.py
@@ -1,4 +1,7 @@
 import os
+import stat
+import tarfile
+import zlib
 from collections.abc import Callable, Generator
 from pathlib import Path
 
@@ -71,3 +74,54 @@ def file_iterator(file_path: str, chunk_size: int = 64 * 1024) -> Generator[byte
     with open(file_path, "rb") as file:
         while chunk := file.read(chunk_size):
             yield chunk
+
+
+def _tar_entries(root: Path, chunk_size: int) -> Generator[bytes]:
+    """Yield an uncompressed tar of the regular files below `root`, one chunk at a time."""
+    for directory, _, files in os.walk(root):
+        for file in sorted(files):
+            file_path = Path(directory) / file
+            file_stat = file_path.lstat()
+            if not stat.S_ISREG(file_stat.st_mode):
+                continue
+
+            info = tarfile.TarInfo(str(file_path.relative_to(root)))
+            info.size = file_stat.st_size
+            info.mtime = int(file_stat.st_mtime)
+            info.mode = stat.S_IMODE(file_stat.st_mode)
+            yield info.tobuf(tarfile.PAX_FORMAT)
+
+            remaining = info.size
+            with open(file_path, "rb") as f:
+                while remaining and (chunk := f.read(min(chunk_size, remaining))):
+                    remaining -= len(chunk)
+                    yield chunk
+            # A file that shrank while being read is zero-filled, so the header stays true.
+            padding = remaining + (-info.size % tarfile.BLOCKSIZE)
+            while padding:
+                chunk_length = min(chunk_size, padding)
+                padding -= chunk_length
+                yield bytes(chunk_length)
+
+    yield bytes(2 * tarfile.BLOCKSIZE)
+
+
+def tar_gz_iterator(root: Path, chunk_size: int = 64 * 1024) -> Generator[bytes]:
+    """
+    Stream a gzipped tar of the regular files below a directory
+
+    Memory use is bounded by `chunk_size`, whatever the size of the files.
+    Symlinks and other special files are left out.
+
+    Parameters
+    ----------
+    root
+        Directory to archive, which becomes the root of the archive
+    chunk_size
+        Size of each chunk to read from the files
+    """
+    compressor = zlib.compressobj(wbits=zlib.MAX_WBITS | 16)
+    for data in _tar_entries(root, chunk_size):
+        if compressed := compressor.compress(data):
+            yield compressed
+    yield compressor.flush()
diff --git a/backend/src/ref_backend/models/diagnostics.py b/backend/src/ref_backend/models/diagnostics.py
index a44db7c1..73d33f27 100644
--- a/backend/src/ref_backend/models/diagnostics.py
+++ b/backend/src/ref_backend/models/diagnostics.py
@@ -64,10 +64,6 @@ class DiagnosticCatalogEntry(BaseModel):
     """
     Description of the diagnostic
     """
-    execution_groups: list[int]
-    """
-    List of IDs for the provider executions associated with this provider
-    """
     groups: GroupCounts
     """
     Execution groups at the promoted version, by the outcome of their latest execution
@@ -109,9 +105,8 @@ def _ensure_metadata_cache(app_context: "AppContext") -> Mapping[str, Diagnostic
         return load_diagnostic_metadata_cached(app_context.settings.diagnostic_metadata_path_resolved)
 
     @staticmethod
-    def _build_group_by_summary(diagnostic: models.Diagnostic, app_context: "AppContext") -> list[GroupBy]:
+    def _build_group_by_summary(concrete_diagnostic: "Diagnostic | None") -> list[GroupBy]:
         """Extract and build group_by information from diagnostic data requirements."""
-        concrete_diagnostic = _concrete_diagnostic(diagnostic, app_context)
         if concrete_diagnostic is None:
             return []
         data_requirements = sorted(
@@ -147,7 +142,7 @@ def _get_aft_link(diagnostic: models.Diagnostic) -> "AFTDiagnosticDetail | None"
         if aft_id:
             return get_aft_diagnostic_by_id(aft_id)
         else:
-            logger.warning(f"No AFT found for diagnostic {diagnostic.provider.slug}/{diagnostic.slug}")
+            logger.debug(f"No AFT found for diagnostic {diagnostic.provider.slug}/{diagnostic.slug}")
             return None
 
     @staticmethod
@@ -183,10 +178,9 @@ def build_with_stats(
     ) -> "DiagnosticCatalogEntry":
         """Build a DiagnosticCatalogEntry with pre-computed statistics to avoid N+1 queries."""
         metadata_cache = DiagnosticCatalogEntry._ensure_metadata_cache(app_context)
-        group_by_summary = DiagnosticCatalogEntry._build_group_by_summary(diagnostic, app_context)
-        aft = DiagnosticCatalogEntry._get_aft_link(diagnostic)
-
         concrete_diagnostic = _concrete_diagnostic(diagnostic, app_context)
+        group_by_summary = DiagnosticCatalogEntry._build_group_by_summary(concrete_diagnostic)
+        aft = DiagnosticCatalogEntry._get_aft_link(diagnostic)
         description = (concrete_diagnostic.__doc__ or "") if concrete_diagnostic else ""
 
         # Build the base diagnostic summary
@@ -196,7 +190,6 @@ def build_with_stats(
             slug=diagnostic.slug,
             name=diagnostic.name,
             description=description,
-            execution_groups=[e.id for e in diagnostic.execution_groups],
             groups=groups,
             promoted_version=diagnostic.promoted_version,
             group_by=group_by_summary,
diff --git a/backend/tests/test_api/test_routes/test_executions.py b/backend/tests/test_api/test_routes/test_executions.py
index 175b353e..20bd1309 100644
--- a/backend/tests/test_api/test_routes/test_executions.py
+++ b/backend/tests/test_api/test_routes/test_executions.py
@@ -1,3 +1,6 @@
+import io
+import tarfile
+
 import pytest
 from fastapi.testclient import TestClient
 
@@ -498,6 +501,8 @@ def test_execution_logs(client: TestClient, settings, monkeypatch, tmp_path):
 
     assert r.status_code == 200
     assert r.text == log_file.read_text()
+    latest_id = client.get(f"{settings.API_V1_STR}/executions/{group_id}/execution").json()["id"]
+    assert r.headers["content-disposition"] == f"attachment; filename=execution_result_{latest_id}.log"
 
 
 def test_execution_logs_lines(client: TestClient, settings, monkeypatch, tmp_path):
@@ -657,3 +662,24 @@ def test_execution_value_facets_of_an_unknown_group(client: TestClient, settings
     r = client.get(f"{settings.API_V1_STR}/executions/999999/values/facets", params={"value_type": "scalar"})
 
     assert r.status_code == 404
+
+
+def test_execution_list_limit_capped(client: TestClient, settings) -> None:
+    r = client.get(f"{settings.API_V1_STR}/executions/?limit=1001")
+
+    assert r.status_code == 422
+
+
+def test_execution_archive(client: TestClient, settings, monkeypatch, tmp_path) -> None:
+    group_id = get_execution_group_id(client, settings)
+    (tmp_path / "plots").mkdir()
+    (tmp_path / "diagnostic.json").write_text("{}")
+    (tmp_path / "plots" / "map.png").write_bytes(b"png" * 1000)
+    monkeypatch.setattr(executions_routes, "resolve_artifact", lambda *_: tmp_path)
+
+    r = client.get(f"{settings.API_V1_STR}/executions/{group_id}/archive")
+
+    assert r.status_code == 200
+    with tarfile.open(fileobj=io.BytesIO(r.content), mode="r:gz") as tar:
+        assert sorted(tar.getnames()) == ["diagnostic.json", "plots/map.png"]
+        assert tar.extractfile("plots/map.png").read() == b"png" * 1000
diff --git a/backend/tests/test_core/test_file_handling.py b/backend/tests/test_core/test_file_handling.py
index 27067e46..bc7b911d 100644
--- a/backend/tests/test_core/test_file_handling.py
+++ b/backend/tests/test_core/test_file_handling.py
@@ -1,6 +1,11 @@
-"""Tests for chunked file reading used by the log-download endpoint."""
+"""Tests for the chunked file reading behind the log and archive downloads."""
 
-from ref_backend.core.file_handling import file_iterator, tail_lines
+import io
+import os
+import tarfile
+import tracemalloc
+
+from ref_backend.core.file_handling import _tar_entries, file_iterator, tail_lines, tar_gz_iterator
 
 
 class TestFileIterator:
@@ -69,3 +74,63 @@ def test_invalid_utf8_is_replaced(self, tmp_path):
         file_path.write_bytes(b"ok\n\xff bad\n")
 
         assert tail_lines(file_path, 5) == ["ok", "\ufffd bad"]
+
+
+def _read_archive(chunks) -> dict[str, bytes]:
+    with tarfile.open(fileobj=io.BytesIO(b"".join(chunks)), mode="r:gz") as tar:
+        return {m.name: tar.extractfile(m).read() for m in tar.getmembers()}
+
+
+class TestTarGzIterator:
+    """Test streaming a directory as a tar.gz."""
+
+    def test_round_trips_nested_files(self, tmp_path):
+        long_name = "d" * 150
+        (tmp_path / "plots" / long_name).mkdir(parents=True)
+        (tmp_path / "diagnostic.json").write_text("{}")
+        (tmp_path / "empty.txt").write_bytes(b"")
+        (tmp_path / "plots" / long_name / "map.png").write_bytes(os.urandom(3000))
+
+        archive = _read_archive(tar_gz_iterator(tmp_path, chunk_size=1024))
+
+        assert archive == {
+            "diagnostic.json": b"{}",
+            "empty.txt": b"",
+            f"plots/{long_name}/map.png": (tmp_path / "plots" / long_name / "map.png").read_bytes(),
+        }
+
+    def test_empty_directory(self, tmp_path):
+        assert _read_archive(tar_gz_iterator(tmp_path)) == {}
+
+    def test_leaves_out_symlinks(self, tmp_path):
+        (tmp_path / "real.txt").write_text("real")
+        (tmp_path / "link.txt").symlink_to(tmp_path / "real.txt")
+
+        assert _read_archive(tar_gz_iterator(tmp_path)) == {"real.txt": b"real"}
+
+    def test_file_that_shrinks_is_zero_filled(self, tmp_path):
+        """The header records the size first, so a file that shrinks mid-read is padded to match."""
+        path = tmp_path / "log.txt"
+        path.write_bytes(b"x" * 5000)
+        entries = _tar_entries(tmp_path, chunk_size=1024)
+        next(entries)  # the header, which recorded 5000 bytes
+        path.write_bytes(b"y" * 100)
+
+        rest = list(entries)
+
+        assert max(len(chunk) for chunk in rest) <= 1024
+        assert b"".join(rest)[:5000] == b"y" * 100 + bytes(4900)
+
+    def test_memory_does_not_grow_with_file_size(self, tmp_path):
+        # Random bytes do not compress, so holding the file would show up as 4 MB.
+        (tmp_path / "big.nc").write_bytes(os.urandom(4 * 1024 * 1024))
+
+        tracemalloc.start()
+        try:
+            for _ in tar_gz_iterator(tmp_path, chunk_size=16 * 1024):
+                pass
+            _, peak = tracemalloc.get_traced_memory()
+        finally:
+            tracemalloc.stop()
+
+        assert peak < 1024 * 1024
diff --git a/changelog/172.breaking.md b/changelog/172.breaking.md
new file mode 100644
index 00000000..351a5dce
--- /dev/null
+++ b/changelog/172.breaking.md
@@ -0,0 +1,2 @@
+Removed the unused `execution_groups` list of ids from diagnostic summaries in the API.
+`GET /executions/` now rejects a `limit` above 1000 with a 422 error, so use `limit` and `offset` to page through more groups.
diff --git a/changelog/172.fix.md b/changelog/172.fix.md
new file mode 100644
index 00000000..154ee27c
--- /dev/null
+++ b/changelog/172.fix.md
@@ -0,0 +1 @@
+Log downloads are now named after the execution, rather than `execution_result_None.log`.
diff --git a/changelog/172.improvement.md b/changelog/172.improvement.md
new file mode 100644
index 00000000..2ec24431
--- /dev/null
+++ b/changelog/172.improvement.md
@@ -0,0 +1,2 @@
+Execution archive downloads now start straight away and use little server memory, however large the outputs.
+Symbolic links in an execution's output folder are no longer included in the archive.
diff --git a/frontend/src/client/types.gen.ts b/frontend/src/client/types.gen.ts
index fab10203..d1074d13 100644
--- a/frontend/src/client/types.gen.ts
+++ b/frontend/src/client/types.gen.ts
@@ -657,10 +657,6 @@ export type DiagnosticCatalogEntry = {
      * Description
      */
     description: string;
-    /**
-     * Execution Groups
-     */
-    execution_groups: Array<number>;
     groups: GroupCounts;
     /**
      * Promoted Version
@@ -737,10 +733,6 @@ export type DiagnosticSummary = {
      * Description
      */
     description: string;
-    /**
-     * Execution Groups
-     */
-    execution_groups: Array<number>;
     groups: GroupCounts;
     /**
      * Promoted Version
diff --git a/frontend/src/lib/resourceUsageCsv.test.ts b/frontend/src/lib/resourceUsageCsv.test.ts
index 23a11181..62f34088 100644
--- a/frontend/src/lib/resourceUsageCsv.test.ts
+++ b/frontend/src/lib/resourceUsageCsv.test.ts
@@ -5,7 +5,6 @@ import { resourceUsageCsv } from "./resourceUsageCsv";
 const base = {
   id: 1,
   description: "",
-  execution_groups: [],
   has_metric_values: false,
   has_scalar_values: false,
   has_series_values: false,