Add get_db_overview for fast, lightweight run listing

docs/changes/newsfragments/8266.new

@@ -0,0 +1,7 @@
+Added :func:`qcodes.dataset.get_db_overview`, a fast way to list the runs in a
+QCoDeS database. It fetches run metadata (experiment/sample names, timestamps,
+record counts and guids) via a single ``JOIN`` query on the ``runs`` and
+``experiments`` tables, without instantiating a ``DataSet`` object per run,
+making it possible to list databases with many thousands of runs almost
+instantly. The returned :class:`qcodes.dataset.RunOverviewDict` is also exported
+on the public ``qcodes.dataset`` namespace.

src/qcodes/dataset/__init__.py

@@ -56,6 +56,7 @@
     initialise_or_create_database_at,
     initialised_database_at,
 )
+from .sqlite.db_overview import RunOverviewDict, get_db_overview
 from .sqlite.settings import SQLiteSettings
 from .threading import (
     SequentialParamsCaller,
@@ -79,6 +80,7 @@
     "ParamSpec",
     "ParamSpecTree",
     "RunDescriber",
+    "RunOverviewDict",
     "SQLiteSettings",
     "SequentialParamsCaller",
     "ThreadPoolParamsCaller",
@@ -95,6 +97,7 @@
     "export_datasets_and_create_metadata_db",
     "extract_runs_into_db",
     "get_data_export_path",
+    "get_db_overview",
     "get_default_experiment_id",
     "get_guids_by_run_spec",
     "guids_from_dbs",

src/qcodes/dataset/sqlite/db_overview.py

@@ -0,0 +1,253 @@
+"""
+This module provides a fast, lightweight overview of the runs stored in a
+QCoDeS database.
+
+:func:`get_db_overview` issues a single ``JOIN`` query against the ``runs`` and
+``experiments`` tables to collect run metadata (experiment/sample names, time
+stamps, record counts, guids, ...) without instantiating a ``DataSet`` object
+per run. This avoids the expensive ``experiments()`` + ``data_sets()``
+enumeration and makes it possible to list the contents of databases with many
+thousands of runs almost instantly. It is primarily intended for tools that
+need to display a table of runs (e.g. dataset browsers).
+
+The queries rely on the stable QCoDeS database schema (the ``runs`` and
+``experiments`` tables) which has been unchanged across many QCoDeS versions.
+"""
+
+from __future__ import annotations
+
+import datetime
+import json
+import logging
+from contextlib import closing, nullcontext
+from typing import TYPE_CHECKING
+
+from typing_extensions import TypedDict
+
+from qcodes.dataset.sqlite.database import conn_from_dbpath_or_conn
+from qcodes.dataset.sqlite.query_helpers import is_column_in_table
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+    from pathlib import Path
+
+    from qcodes.dataset.sqlite.connection import AtomicConnection
+
+log = logging.getLogger(__name__)
+
+
+class RunOverviewDict(TypedDict):
+    """
+    Lightweight overview of a single run.
+
+    Contains only cheap-to-query metadata: no snapshot, no data and no full
+    ``DataSet`` object. Extra ad-hoc metadata columns requested via the
+    ``extra_columns`` argument of :func:`get_db_overview` are added to the
+    dictionary under their column name in addition to the keys documented here.
+    """
+
+    #: ``run_id`` of the run.
+    run_id: int
+    #: Name of the experiment the run belongs to.
+    experiment: str
+    #: Sample name of the experiment the run belongs to.
+    sample: str
+    #: Name of the run.
+    name: str
+    #: Local date the run was started, formatted as ``YYYY-MM-DD`` (empty
+    #: string if unknown).
+    started_date: str
+    #: Local time the run was started, formatted as ``HH:MM:SS`` (empty string
+    #: if unknown).
+    started_time: str
+    #: Local date the run was completed, formatted as ``YYYY-MM-DD`` (empty
+    #: string if the run has not completed).
+    completed_date: str
+    #: Local time the run was completed, formatted as ``HH:MM:SS`` (empty
+    #: string if the run has not completed).
+    completed_time: str
+    #: Best-effort number of data points in the run, see :func:`get_db_overview`.
+    records: int
+    #: guid of the run.
+    guid: str
+
+
+def _format_timestamp(ts: float | None) -> tuple[str, str]:
+    """
+    Convert a unix timestamp into ``(date, time)`` strings in local time.
+
+    Returns a pair of empty strings if the timestamp is missing or invalid.
+    """
+    if ts is None or ts == 0:
+        return "", ""
+    try:
+        dt = datetime.datetime.fromtimestamp(ts)
+    except (OSError, ValueError, OverflowError):
+        return "", ""
+    return dt.strftime("%Y-%m-%d"), dt.strftime("%H:%M:%S")
+
+
+def _records_from_run_description(run_description_json: str | None) -> int:
+    """
+    Extract a data-point count from the ``shapes`` field of a run description.
+
+    A QCoDeS run description may contain a ``shapes`` mapping from dependent
+    parameter names to their shape tuples. The count returned here is the sum
+    over all dependent parameters of the product of their shape dimensions.
+    Returns ``0`` if the run description is missing, cannot be parsed or does
+    not contain shape information.
+    """
+    if not run_description_json:
+        return 0
+    try:
+        desc = json.loads(run_description_json)
+    except (json.JSONDecodeError, TypeError):
+        return 0
+    shapes = desc.get("shapes") if isinstance(desc, dict) else None
+    if not shapes:
+        return 0
+    total = 0
+    for shape in shapes.values():
+        if isinstance(shape, (list, tuple)) and len(shape) > 0:
+            n = 1
+            for dim in shape:
+                n *= dim
+            total += n
+    return total
+
+
+def get_db_overview(
+    path_to_db: str | Path | None = None,
+    conn: AtomicConnection | None = None,
+    start_run_id: int = 0,
+    extra_columns: Sequence[str] | None = None,
+) -> dict[int, RunOverviewDict]:
+    """
+    Get a lightweight overview of the runs in a QCoDeS database.
+
+    This uses a single SQL ``JOIN`` query on the ``runs`` and ``experiments``
+    tables to fetch run metadata, avoiding the much more expensive
+    ``experiments()`` + ``data_sets()`` enumeration that instantiates a
+    ``DataSet`` object per run. It is therefore well suited for listing the
+    contents of databases with many runs.
+
+    The reported number of ``records`` is a best-effort estimate of the number
+    of data points in a run:
+
+    * For completed runs the shape information stored in the run description is
+      preferred (it is the authoritative final count), falling back to the
+      number of rows in the results table.
+    * For runs that are still in progress the number of rows in the results
+      table is preferred (it grows as data is added), falling back to the run
+      description shapes.
+    * If neither is available the ``result_counter`` of the run is used, which
+      counts the number of insertions rather than data points.
+
+    Only one of ``path_to_db`` and ``conn`` should be supplied. If a
+    ``path_to_db`` is given the database is opened in read-only mode and the
+    connection is closed again before returning.
+
+    Args:
+        path_to_db: Path to the database file. Opened read-only if given.
+        conn: An existing connection to use instead of ``path_to_db``. It is
+            left open by this function.
+        start_run_id: Only return runs whose ``run_id`` is strictly greater
+            than this value. Use ``0`` (the default) to get all runs, or pass
+            the last known ``run_id`` to fetch only newly added runs.
+        extra_columns: Names of additional ``runs``-table columns to include in
+            each :class:`RunOverviewDict`. Columns that do not exist in the
+            ``runs`` table of the given database are silently skipped. This is
+            useful for reading ad-hoc metadata columns added via
+            ``DataSet.add_metadata``.
+
+    Returns:
+        A dictionary mapping ``run_id`` to a :class:`RunOverviewDict`.
+
+    """
+    overview: dict[int, RunOverviewDict] = {}
+
+    created_conn = conn is None
+    connection = conn_from_dbpath_or_conn(
+        conn=conn, path_to_db=path_to_db, read_only=True
+    )
+    manager = closing(connection) if created_conn else nullcontext(connection)
+
+    with manager as c:
+        valid_extra_columns = [
+            col for col in (extra_columns or []) if is_column_in_table(c, "runs", col)
+        ]
+        extra_select = "".join(f", r.{col}" for col in valid_extra_columns)
+
+        # ``run_description`` is queried to derive the record count for
+        # completed runs; the (potentially large) snapshot is deliberately
+        # excluded.
+        query = f"""
+            SELECT r.run_id, e.name, e.sample_name, r.name,
+                   r.run_timestamp, r.completed_timestamp,
+                   r.result_counter, r.guid, r.result_table_name,
+                   r.run_description{extra_select}
+            FROM runs r
+            JOIN experiments e ON r.exp_id = e.exp_id
+            WHERE r.run_id > ?
+            ORDER BY r.run_id
+        """
+
+        try:
+            rows = c.execute(query, (start_run_id,)).fetchall()
+        except Exception as e:
+            log.warning("Could not query database overview: %s", e)
+            return overview
+
+        # ``result_counter`` in the runs table counts INSERT calls, not data
+        # points. For the ``array`` paramtype a single INSERT can contain many
+        # data points, so the real row count of the results table is queried
+        # separately.
+        result_tables = {row[8] for row in rows if row[8]}
+        row_counts: dict[str, int] = {}
+        for table in result_tables:
+            try:
+                count = c.execute(f'SELECT COUNT(*) FROM "{table}"').fetchone()
+            except Exception:
+                continue  # results table may not exist yet
+            row_counts[table] = count[0] if count else 0
+
+        n_fixed = 10  # number of columns selected before ``extra_columns``
+        for row in rows:
+            run_id = row[0]
+            started_date, started_time = _format_timestamp(row[4])
+            completed_date, completed_time = _format_timestamp(row[5])
+            result_table = row[8] or ""
+            is_completed = row[5] is not None and row[5] != 0
+
+            if is_completed:
+                records = _records_from_run_description(row[9])
+                if records == 0:
+                    records = row_counts.get(result_table, 0)
+            else:
+                records = row_counts.get(result_table, 0)
+                if records == 0:
+                    records = _records_from_run_description(row[9])
+            if records == 0:
+                records = row[6] or 0
+
+            entry: RunOverviewDict = {
+                "run_id": run_id,
+                "experiment": row[1] or "",
+                "sample": row[2] or "",
+                "name": row[3] or "",
+                "started_date": started_date,
+                "started_time": started_time,
+                "completed_date": completed_date,
+                "completed_time": completed_time,
+                "records": records,
+                "guid": row[7] or "",
+            }
+            if valid_extra_columns:
+                extra = {
+                    col: row[n_fixed + i] for i, col in enumerate(valid_extra_columns)
+                }
+                entry.update(extra)  # type: ignore[typeddict-item]
+
+            overview[run_id] = entry
+
+    return overview