apdbSql.py

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# This file is part of dax_apdb.
#
# Developed for the LSST Data Management System.
# This product includes software developed by the LSST Project
# (http://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
# for details of code ownership.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
"""Module defining Apdb class and related methods.
"""
 
from __future__ import annotations
 
__all__ = ["ApdbSqlConfig", "ApdbSql"]
 
from contextlib import contextmanager
import logging
import numpy as np
import pandas
from typing import Any, Dict, Iterable, Iterator, List, Optional, Tuple
 
import lsst.daf.base as dafBase
from lsst.pex.config import Field, ChoiceField, ListField
from lsst.sphgeom import HtmPixelization, LonLat, Region, UnitVector3d
import sqlalchemy
from sqlalchemy import (func, sql)
from sqlalchemy.pool import NullPool
from .apdb import Apdb, ApdbConfig
from .apdbSchema import ApdbTables, TableDef
from .apdbSqlSchema import ApdbSqlSchema
from .timer import Timer
 
 
_LOG = logging.getLogger(__name__)
 
 
def _split(seq: Iterable, nItems: int) -> Iterator[List]:
    """Split a sequence into smaller sequences"""
    seq = list(seq)
    while seq:
        yield seq[:nItems]
        del seq[:nItems]
 
 
def _coerce_uint64(df: pandas.DataFrame) -> pandas.DataFrame:
    """Change type of the uint64 columns to int64, return copy of data frame.
    """
    names = [c[0] for c in df.dtypes.items() if c[1] == np.uint64]
    return df.astype({name: np.int64 for name in names})
 
 
def _make_midPointTai_start(visit_time: dafBase.DateTime, months: int) -> float:
    """Calculate starting point for time-based source search.
 
    Parameters
    ----------
    visit_time : `lsst.daf.base.DateTime`
        Time of current visit.
    months : `int`
        Number of months in the sources history.
 
    Returns
    -------
    time : `float`
        A ``midPointTai`` starting point, MJD time.
    """
    # TODO: `system` must be consistent with the code in ap_association
    # (see DM-31996)
    return visit_time.get(system=dafBase.DateTime.MJD) - months * 30
 
 
@contextmanager
def _ansi_session(engine: sqlalchemy.engine.Engine) -> Iterator[sqlalchemy.engine.Connection]:
    """Returns a connection, makes sure that ANSI mode is set for MySQL
    """
    with engine.begin() as conn:
        if engine.name == 'mysql':
            conn.execute(sql.text("SET SESSION SQL_MODE = 'ANSI'"))
        yield conn
    return
 
 
class ApdbSqlConfig(ApdbConfig):
    """APDB configuration class for SQL implementation (ApdbSql).
    """
    db_url = Field(
        dtype=str,
        doc="SQLAlchemy database connection URI"
    )
    isolation_level = ChoiceField(
        dtype=str,
        doc="Transaction isolation level, if unset then backend-default value "
            "is used, except for SQLite backend where we use READ_UNCOMMITTED. "
            "Some backends may not support every allowed value.",
        allowed={
            "READ_COMMITTED": "Read committed",
            "READ_UNCOMMITTED": "Read uncommitted",
            "REPEATABLE_READ": "Repeatable read",
            "SERIALIZABLE": "Serializable"
        },
        default=None,
        optional=True
    )
    connection_pool = Field(
        dtype=bool,
        doc="If False then disable SQLAlchemy connection pool. "
            "Do not use connection pool when forking.",
        default=True
    )
    connection_timeout = Field(
        dtype=float,
        doc="Maximum time to wait time for database lock to be released before "
            "exiting. Defaults to sqlachemy defaults if not set.",
        default=None,
        optional=True
    )
    sql_echo = Field(
        dtype=bool,
        doc="If True then pass SQLAlchemy echo option.",
        default=False
    )
    dia_object_index = ChoiceField(
        dtype=str,
        doc="Indexing mode for DiaObject table",
        allowed={
            'baseline': "Index defined in baseline schema",
            'pix_id_iov': "(pixelId, objectId, iovStart) PK",
            'last_object_table': "Separate DiaObjectLast table"
        },
        default='baseline'
    )
    htm_level = Field(
        dtype=int,
        doc="HTM indexing level",
        default=20
    )
    htm_max_ranges = Field(
        dtype=int,
        doc="Max number of ranges in HTM envelope",
        default=64
    )
    htm_index_column = Field(
        dtype=str,
        default="pixelId",
        doc="Name of a HTM index column for DiaObject and DiaSource tables"
    )
    ra_dec_columns = ListField(
        dtype=str,
        default=["ra", "decl"],
        doc="Names ra/dec columns in DiaObject table"
    )
    dia_object_columns = ListField(
        dtype=str,
        doc="List of columns to read from DiaObject, by default read all columns",
        default=[]
    )
    object_last_replace = Field(
        dtype=bool,
        doc="If True (default) then use \"upsert\" for DiaObjectsLast table",
        default=True
    )
    prefix = Field(
        dtype=str,
        doc="Prefix to add to table names and index names",
        default=""
    )
    explain = Field(
        dtype=bool,
        doc="If True then run EXPLAIN SQL command on each executed query",
        default=False
    )
    timer = Field(
        dtype=bool,
        doc="If True then print/log timing information",
        default=False
    )
 
    def validate(self) -> None:
        super().validate()
        if len(self.ra_dec_columnsra_dec_columns) != 2:
            raise ValueError("ra_dec_columns must have exactly two column names")
 
 
class ApdbSql(Apdb):
    """Implementation of APDB interface based on SQL database.
 
    The implementation is configured via standard ``pex_config`` mechanism
    using `ApdbSqlConfig` configuration class. For an example of different
    configurations check ``config/`` folder.
 
    Parameters
    ----------
    config : `ApdbSqlConfig`
        Configuration object.
    """
 
    ConfigClass = ApdbSqlConfig
 
    def __init__(self, config: ApdbSqlConfig):
 
        self.configconfig = config
 
        _LOG.debug("APDB Configuration:")
        _LOG.debug("    dia_object_index: %s", self.configconfig.dia_object_index)
        _LOG.debug("    read_sources_months: %s", self.configconfig.read_sources_months)
        _LOG.debug("    read_forced_sources_months: %s", self.configconfig.read_forced_sources_months)
        _LOG.debug("    dia_object_columns: %s", self.configconfig.dia_object_columns)
        _LOG.debug("    object_last_replace: %s", self.configconfig.object_last_replace)
        _LOG.debug("    schema_file: %s", self.configconfig.schema_file)
        _LOG.debug("    extra_schema_file: %s", self.configconfig.extra_schema_file)
        _LOG.debug("    schema prefix: %s", self.configconfig.prefix)
 
        # engine is reused between multiple processes, make sure that we don't
        # share connections by disabling pool (by using NullPool class)
        kw = dict(echo=self.configconfig.sql_echo)
        conn_args: Dict[str, Any] = dict()
        if not self.configconfig.connection_pool:
            kw.update(poolclass=NullPool)
        if self.configconfig.isolation_level is not None:
            kw.update(isolation_level=self.configconfig.isolation_level)
        elif self.configconfig.db_url.startswith("sqlite"):
            # Use READ_UNCOMMITTED as default value for sqlite.
            kw.update(isolation_level="READ_UNCOMMITTED")
        if self.configconfig.connection_timeout is not None:
            if self.configconfig.db_url.startswith("sqlite"):
                conn_args.update(timeout=self.configconfig.connection_timeout)
            elif self.configconfig.db_url.startswith(("postgresql", "mysql")):
                conn_args.update(connect_timeout=self.configconfig.connection_timeout)
        kw.update(connect_args=conn_args)
        self._engine_engine = sqlalchemy.create_engine(self.configconfig.db_url, **kw)
 
        self._schema_schema = ApdbSqlSchema(engine=self._engine_engine,
                                     dia_object_index=self.configconfig.dia_object_index,
                                     schema_file=self.configconfig.schema_file,
                                     extra_schema_file=self.configconfig.extra_schema_file,
                                     prefix=self.configconfig.prefix,
                                     htm_index_column=self.configconfig.htm_index_column)
 
        self.pixelatorpixelator = HtmPixelization(self.configconfig.htm_level)
 
    def tableRowCount(self) -> Dict[str, int]:
        """Returns dictionary with the table names and row counts.
 
        Used by ``ap_proto`` to keep track of the size of the database tables.
        Depending on database technology this could be expensive operation.
 
        Returns
        -------
        row_counts : `dict`
            Dict where key is a table name and value is a row count.
        """
        res = {}
        tables: List[sqlalchemy.schema.Table] = [
            self._schema_schema.objects, self._schema_schema.sources, self._schema_schema.forcedSources]
        if self.configconfig.dia_object_index == 'last_object_table':
            tables.append(self._schema_schema.objects_last)
        for table in tables:
            stmt = sql.select([func.count()]).select_from(table)
            count = self._engine_engine.scalar(stmt)
            res[table.name] = count
 
        return res
 
    def tableDef(self, table: ApdbTables) -> Optional[TableDef]:
        # docstring is inherited from a base class
        return self._schema_schema.tableSchemas.get(table)
 
    def makeSchema(self, drop: bool = False) -> None:
        # docstring is inherited from a base class
        self._schema_schema.makeSchema(drop=drop)
 
    def getDiaObjects(self, region: Region) -> pandas.DataFrame:
        # docstring is inherited from a base class
 
        # decide what columns we need
        table: sqlalchemy.schema.Table
        if self.configconfig.dia_object_index == 'last_object_table':
            table = self._schema_schema.objects_last
        else:
            table = self._schema_schema.objects
        if not self.configconfig.dia_object_columns:
            query = table.select()
        else:
            columns = [table.c[col] for col in self.configconfig.dia_object_columns]
            query = sql.select(columns)
 
        # build selection
        htm_index_column = table.columns[self.configconfig.htm_index_column]
        exprlist = []
        pixel_ranges = self._htm_indices_htm_indices(region)
        for low, upper in pixel_ranges:
            upper -= 1
            if low == upper:
                exprlist.append(htm_index_column == low)
            else:
                exprlist.append(sql.expression.between(htm_index_column, low, upper))
        query = query.where(sql.expression.or_(*exprlist))
 
        # select latest version of objects
        if self.configconfig.dia_object_index != 'last_object_table':
            query = query.where(table.c.validityEnd == None)  # noqa: E711
 
        _LOG.debug("query: %s", query)
 
        if self.configconfig.explain:
            # run the same query with explain
            self._explain_explain(query, self._engine_engine)
 
        # execute select
        with Timer('DiaObject select', self.configconfig.timer):
            with self._engine_engine.begin() as conn:
                objects = pandas.read_sql_query(query, conn)
        _LOG.debug("found %s DiaObjects", len(objects))
        return objects
 
    def getDiaSources(self, region: Region,
                      object_ids: Optional[Iterable[int]],
                      visit_time: dafBase.DateTime) -> Optional[pandas.DataFrame]:
        # docstring is inherited from a base class
        if self.configconfig.read_sources_months == 0:
            _LOG.debug("Skip DiaSources fetching")
            return None
 
        if object_ids is None:
            # region-based select
            return self._getDiaSourcesInRegion_getDiaSourcesInRegion(region, visit_time)
        else:
            return self._getDiaSourcesByIDs_getDiaSourcesByIDs(list(object_ids), visit_time)
 
    def getDiaForcedSources(self, region: Region,
                            object_ids: Optional[Iterable[int]],
                            visit_time: dafBase.DateTime) -> Optional[pandas.DataFrame]:
        """Return catalog of DiaForcedSource instances from a given region.
 
        Parameters
        ----------
        region : `lsst.sphgeom.Region`
            Region to search for DIASources.
        object_ids : iterable [ `int` ], optional
            List of DiaObject IDs to further constrain the set of returned
            sources. If list is empty then empty catalog is returned with a
            correct schema.
        visit_time : `lsst.daf.base.DateTime`
            Time of the current visit.
 
        Returns
        -------
        catalog : `pandas.DataFrame`, or `None`
            Catalog containing DiaSource records. `None` is returned if
            ``read_sources_months`` configuration parameter is set to 0.
 
        Raises
        ------
        NotImplementedError
            Raised if ``object_ids`` is `None`.
 
        Notes
        -----
        Even though base class allows `None` to be passed for ``object_ids``,
        this class requires ``object_ids`` to be not-`None`.
        `NotImplementedError` is raised if `None` is passed.
 
        This method returns DiaForcedSource catalog for a region with additional
        filtering based on DiaObject IDs. Only a subset of DiaSource history
        is returned limited by ``read_forced_sources_months`` config parameter,
        w.r.t. ``visit_time``. If ``object_ids`` is empty then an empty catalog
        is always returned with a correct schema (columns/types).
        """
 
        if self.configconfig.read_forced_sources_months == 0:
            _LOG.debug("Skip DiaForceSources fetching")
            return None
 
        if object_ids is None:
            # This implementation does not support region-based selection.
            raise NotImplementedError("Region-based selection is not supported")
 
        # TODO: DateTime.MJD must be consistent with code in ap_association,
        # alternatively we can fill midPointTai ourselves in store()
        midPointTai_start = _make_midPointTai_start(visit_time, self.configconfig.read_forced_sources_months)
        _LOG.debug("midPointTai_start = %.6f", midPointTai_start)
 
        table: sqlalchemy.schema.Table = self._schema_schema.forcedSources
        with Timer('DiaForcedSource select', self.configconfig.timer):
            sources = self._getSourcesByIDs_getSourcesByIDs(table, list(object_ids), midPointTai_start)
 
        _LOG.debug("found %s DiaForcedSources", len(sources))
        return sources
 
    def store(self,
              visit_time: dafBase.DateTime,
              objects: pandas.DataFrame,
              sources: Optional[pandas.DataFrame] = None,
              forced_sources: Optional[pandas.DataFrame] = None) -> None:
        # docstring is inherited from a base class
 
        # fill pixelId column for DiaObjects
        objects = self._add_obj_htm_index_add_obj_htm_index(objects)
        self._storeDiaObjects_storeDiaObjects(objects, visit_time)
 
        if sources is not None:
            # copy pixelId column from DiaObjects to DiaSources
            sources = self._add_src_htm_index_add_src_htm_index(sources, objects)
            self._storeDiaSources_storeDiaSources(sources)
 
        if forced_sources is not None:
            self._storeDiaForcedSources_storeDiaForcedSources(forced_sources)
 
    def dailyJob(self) -> None:
        # docstring is inherited from a base class
 
        if self._engine_engine.name == 'postgresql':
 
            # do VACUUM on all tables
            _LOG.info("Running VACUUM on all tables")
            connection = self._engine_engine.raw_connection()
            ISOLATION_LEVEL_AUTOCOMMIT = 0
            connection.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)
            cursor = connection.cursor()
            cursor.execute("VACUUM ANALYSE")
 
    def countUnassociatedObjects(self) -> int:
        # docstring is inherited from a base class
 
        # Retrieve the DiaObject table.
        table: sqlalchemy.schema.Table = self._schema_schema.objects
 
        # Construct the sql statement.
        stmt = sql.select([func.count()]).select_from(table).where(table.c.nDiaSources == 1)
        stmt = stmt.where(table.c.validityEnd == None)  # noqa: E711
 
        # Return the count.
        with self._engine_engine.begin() as conn:
            count = conn.scalar(stmt)
 
        return count
 
    def _getDiaSourcesInRegion(self, region: Region, visit_time: dafBase.DateTime
                               ) -> pandas.DataFrame:
        """Returns catalog of DiaSource instances from given region.
 
        Parameters
        ----------
        region : `lsst.sphgeom.Region`
            Region to search for DIASources.
        visit_time : `lsst.daf.base.DateTime`
            Time of the current visit.
 
        Returns
        -------
        catalog : `pandas.DataFrame`
            Catalog containing DiaSource records.
        """
        # TODO: DateTime.MJD must be consistent with code in ap_association,
        # alternatively we can fill midPointTai ourselves in store()
        midPointTai_start = _make_midPointTai_start(visit_time, self.configconfig.read_sources_months)
        _LOG.debug("midPointTai_start = %.6f", midPointTai_start)
 
        table: sqlalchemy.schema.Table = self._schema_schema.sources
        query = table.select()
 
        # build selection
        htm_index_column = table.columns[self.configconfig.htm_index_column]
        exprlist = []
        pixel_ranges = self._htm_indices_htm_indices(region)
        for low, upper in pixel_ranges:
            upper -= 1
            if low == upper:
                exprlist.append(htm_index_column == low)
            else:
                exprlist.append(sql.expression.between(htm_index_column, low, upper))
        time_filter = table.columns["midPointTai"] > midPointTai_start
        where = sql.expression.and_(sql.expression.or_(*exprlist), time_filter)
        query = query.where(where)
 
        # execute select
        with Timer('DiaSource select', self.configconfig.timer):
            with _ansi_session(self._engine_engine) as conn:
                sources = pandas.read_sql_query(query, conn)
        _LOG.debug("found %s DiaSources", len(sources))
        return sources
 
    def _getDiaSourcesByIDs(self, object_ids: List[int], visit_time: dafBase.DateTime
                            ) -> pandas.DataFrame:
        """Returns catalog of DiaSource instances given set of DiaObject IDs.
 
        Parameters
        ----------
        object_ids :
            Collection of DiaObject IDs
        visit_time : `lsst.daf.base.DateTime`
            Time of the current visit.
 
        Returns
        -------
        catalog : `pandas.DataFrame`
            Catalog contaning DiaSource records.
        """
        # TODO: DateTime.MJD must be consistent with code in ap_association,
        # alternatively we can fill midPointTai ourselves in store()
        midPointTai_start = _make_midPointTai_start(visit_time, self.configconfig.read_sources_months)
        _LOG.debug("midPointTai_start = %.6f", midPointTai_start)
 
        table: sqlalchemy.schema.Table = self._schema_schema.sources
        with Timer('DiaSource select', self.configconfig.timer):
            sources = self._getSourcesByIDs_getSourcesByIDs(table, object_ids, midPointTai_start)
 
        _LOG.debug("found %s DiaSources", len(sources))
        return sources
 
    def _getSourcesByIDs(self, table: sqlalchemy.schema.Table,
                         object_ids: List[int],
                         midPointTai_start: float
                         ) -> pandas.DataFrame:
        """Returns catalog of DiaSource or DiaForcedSource instances given set
        of DiaObject IDs.
 
        Parameters
        ----------
        table : `sqlalchemy.schema.Table`
            Database table.
        object_ids :
            Collection of DiaObject IDs
        midPointTai_start : `float`
            Earliest midPointTai to retrieve.
 
        Returns
        -------
        catalog : `pandas.DataFrame`
            Catalog contaning DiaSource records. `None` is returned if
            ``read_sources_months`` configuration parameter is set to 0 or
            when ``object_ids`` is empty.
        """
        sources: Optional[pandas.DataFrame] = None
        with _ansi_session(self._engine_engine) as conn:
            if len(object_ids) <= 0:
                _LOG.debug("ID list is empty, just fetch empty result")
                query = table.select().where(False)
                sources = pandas.read_sql_query(query, conn)
            else:
                for ids in _split(sorted(object_ids), 1000):
                    query = f'SELECT *  FROM "{table.name}" WHERE '
 
                    # select by object id
                    ids_str = ",".join(str(id) for id in ids)
                    query += f'"diaObjectId" IN ({ids_str})'
                    query += f' AND "midPointTai" > {midPointTai_start}'
 
                    # execute select
                    df = pandas.read_sql_query(sql.text(query), conn)
                    if sources is None:
                        sources = df
                    else:
                        sources = sources.append(df)
        assert sources is not None, "Catalog cannot be None"
        return sources
 
    def _storeDiaObjects(self, objs: pandas.DataFrame, visit_time: dafBase.DateTime) -> None:
        """Store catalog of DiaObjects from current visit.
 
        Parameters
        ----------
        objs : `pandas.DataFrame`
            Catalog with DiaObject records.
        visit_time : `lsst.daf.base.DateTime`
            Time of the visit.
        """
 
        ids = sorted(objs['diaObjectId'])
        _LOG.debug("first object ID: %d", ids[0])
 
        # NOTE: workaround for sqlite, need this here to avoid
        # "database is locked" error.
        table: sqlalchemy.schema.Table = self._schema_schema.objects
 
        # TODO: Need to verify that we are using correct scale here for
        # DATETIME representation (see DM-31996).
        dt = visit_time.toPython()
 
        # everything to be done in single transaction
        with _ansi_session(self._engine_engine) as conn:
 
            ids_str = ",".join(str(id) for id in ids)
 
            if self.configconfig.dia_object_index == 'last_object_table':
 
                # insert and replace all records in LAST table, mysql and postgres have
                # non-standard features
                table = self._schema_schema.objects_last
                do_replace = self.configconfig.object_last_replace
                # If the input data is of type Pandas, we drop the previous
                # objects regardless of the do_replace setting due to how
                # Pandas inserts objects.
                if not do_replace or isinstance(objs, pandas.DataFrame):
                    query = 'DELETE FROM "' + table.name + '" '
                    query += 'WHERE "diaObjectId" IN (' + ids_str + ') '
 
                    if self.configconfig.explain:
                        # run the same query with explain
                        self._explain_explain(query, conn)
 
                    with Timer(table.name + ' delete', self.configconfig.timer):
                        res = conn.execute(sql.text(query))
                    _LOG.debug("deleted %s objects", res.rowcount)
 
                extra_columns: Dict[str, Any] = dict(lastNonForcedSource=dt)
                with Timer("DiaObjectLast insert", self.configconfig.timer):
                    objs = _coerce_uint64(objs)
                    for col, data in extra_columns.items():
                        objs[col] = data
                    objs.to_sql("DiaObjectLast", conn, if_exists='append',
                                index=False)
            else:
 
                # truncate existing validity intervals
                table = self._schema_schema.objects
                query = 'UPDATE "' + table.name + '" '
                query += "SET \"validityEnd\" = '" + str(dt) + "' "
                query += 'WHERE "diaObjectId" IN (' + ids_str + ') '
                query += 'AND "validityEnd" IS NULL'
 
                # _LOG.debug("query: %s", query)
 
                if self.configconfig.explain:
                    # run the same query with explain
                    self._explain_explain(query, conn)
 
                with Timer(table.name + ' truncate', self.configconfig.timer):
                    res = conn.execute(sql.text(query))
                _LOG.debug("truncated %s intervals", res.rowcount)
 
            # insert new versions
            table = self._schema_schema.objects
            extra_columns = dict(lastNonForcedSource=dt, validityStart=dt,
                                 validityEnd=None)
            with Timer("DiaObject insert", self.configconfig.timer):
                objs = _coerce_uint64(objs)
                for col, data in extra_columns.items():
                    objs[col] = data
                objs.to_sql("DiaObject", conn, if_exists='append',
                            index=False)
 
    def _storeDiaSources(self, sources: pandas.DataFrame) -> None:
        """Store catalog of DiaSources from current visit.
 
        Parameters
        ----------
        sources : `pandas.DataFrame`
            Catalog containing DiaSource records
        """
        # everything to be done in single transaction
        with _ansi_session(self._engine_engine) as conn:
 
            with Timer("DiaSource insert", self.configconfig.timer):
                sources = _coerce_uint64(sources)
                sources.to_sql("DiaSource", conn, if_exists='append', index=False)
 
    def _storeDiaForcedSources(self, sources: pandas.DataFrame) -> None:
        """Store a set of DiaForcedSources from current visit.
 
        Parameters
        ----------
        sources : `pandas.DataFrame`
            Catalog containing DiaForcedSource records
        """
 
        # everything to be done in single transaction
        with _ansi_session(self._engine_engine) as conn:
 
            with Timer("DiaForcedSource insert", self.configconfig.timer):
                sources = _coerce_uint64(sources)
                sources.to_sql("DiaForcedSource", conn, if_exists='append', index=False)
 
    def _explain(self, query: str, conn: sqlalchemy.engine.Connection) -> None:
        """Run the query with explain
        """
 
        _LOG.info("explain for query: %s...", query[:64])
 
        if conn.engine.name == 'mysql':
            query = "EXPLAIN EXTENDED " + query
        else:
            query = "EXPLAIN " + query
 
        res = conn.execute(sql.text(query))
        if res.returns_rows:
            _LOG.info("explain: %s", res.keys())
            for row in res:
                _LOG.info("explain: %s", row)
        else:
            _LOG.info("EXPLAIN returned nothing")
 
    def _htm_indices(self, region: Region) -> List[Tuple[int, int]]:
        """Generate a set of HTM indices covering specified region.
 
        Parameters
        ----------
        region: `sphgeom.Region`
            Region that needs to be indexed.
 
        Returns
        -------
        Sequence of ranges, range is a tuple (minHtmID, maxHtmID).
        """
        _LOG.debug('region: %s', region)
        indices = self.pixelatorpixelator.envelope(region, self.configconfig.htm_max_ranges)
 
        if _LOG.isEnabledFor(logging.DEBUG):
            for irange in indices.ranges():
                _LOG.debug('range: %s %s', self.pixelatorpixelator.toString(irange[0]),
                           self.pixelatorpixelator.toString(irange[1]))
 
        return indices.ranges()
 
    def _add_obj_htm_index(self, df: pandas.DataFrame) -> pandas.DataFrame:
        """Calculate HTM index for each record and add it to a DataFrame.
 
        Notes
        -----
        This overrides any existing column in a DataFrame with the same name
        (pixelId). Original DataFrame is not changed, copy of a DataFrame is
        returned.
        """
        # calculate HTM index for every DiaObject
        htm_index = np.zeros(df.shape[0], dtype=np.int64)
        ra_col, dec_col = self.configconfig.ra_dec_columns
        for i, (ra, dec) in enumerate(zip(df[ra_col], df[dec_col])):
            uv3d = UnitVector3d(LonLat.fromDegrees(ra, dec))
            idx = self.pixelatorpixelator.index(uv3d)
            htm_index[i] = idx
        df = df.copy()
        df[self.configconfig.htm_index_column] = htm_index
        return df
 
    def _add_src_htm_index(self, sources: pandas.DataFrame, objs: pandas.DataFrame) -> pandas.DataFrame:
        """Add pixelId column to DiaSource catalog.
 
        Notes
        -----
        This method copies pixelId value from a matching DiaObject record.
        DiaObject catalog needs to have a pixelId column filled by
        ``_add_obj_htm_index`` method and DiaSource records need to be
        associated to DiaObjects via ``diaObjectId`` column.
 
        This overrides any existing column in a DataFrame with the same name
        (pixelId). Original DataFrame is not changed, copy of a DataFrame is
        returned.
        """
        pixel_id_map: Dict[int, int] = {
            diaObjectId: pixelId for diaObjectId, pixelId
            in zip(objs["diaObjectId"], objs[self.configconfig.htm_index_column])
        }
        # DiaSources associated with SolarSystemObjects do not have an
        # associated DiaObject hence we skip them and set their htmIndex
        # value to 0.
        pixel_id_map[0] = 0
        htm_index = np.zeros(sources.shape[0], dtype=np.int64)
        for i, diaObjId in enumerate(sources["diaObjectId"]):
            htm_index[i] = pixel_id_map[diaObjId]
        sources = sources.copy()
        sources[self.configconfig.htm_index_column] = htm_index
        return sources