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DM-46248: Few small improvements for the new query system #1146

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merged 5 commits into from
Jan 31, 2025
Merged

DM-46248: Few small improvements for the new query system #1146

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3d42102
Fix SQL type of the run column in case it is set to NULL.
andy-slac Nov 11, 2024
488a32d
Skip some dataset searches joins with materialized queries.
andy-slac Nov 21, 2024
e9c7ef5
Set cursor_tuple_fraction parameter for Postgres
andy-slac Jan 9, 2025
1eab6b0
Add indices to temporary tables.
andy-slac Jan 22, 2025
5903c60
Add Query option to suppress DISTINCT in skypix overlaps.
andy-slac Jan 28, 2025
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4 changes: 3 additions & 1 deletion python/lsst/daf/butler/direct_query_driver/_driver.py
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Original file line number Diff line number Diff line change
Expand Up @@ -311,7 +311,9 @@ def materialize(
#
sql_select, _ = plan.finish_select(return_columns=False)
table = self._exit_stack.enter_context(
self.db.temporary_table(make_table_spec(plan.final_columns, self.db, plan.postprocessing))
self.db.temporary_table(
make_table_spec(plan.final_columns, self.db, plan.postprocessing, make_indices=True)
)
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I recall you saying earlier that adding the indexes before doing the inserts sometimes made the inserts much more expensive. Did that get resolved by other changes, or is it just an overall win even if it's occasionally worse.

And would it be worth it to try to move index creation to just after insert in this method?

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That was a false alarm - I have added indices and filling temp table became terribly slow, the real reason was that query planner went into a dumb state on the same exact query (this was before I dropped DISTINCT). With disabled DISTINCT I have not noticed any significant slow down due to indices.
It is true that for bulk data insert it is better to load the data before adding indices. I tried to implement it, but it is not trivial with our code now, the simple idea did not work, and I did not want to start restructuring a bunch of code just for that. Still, if we see it later, it should be possible to delay index creation until after filling the data.

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Just in case we want to do index creation separately later - my initial idea was that I run the same _convertTableSpec but do not add Index instances to Table constructor arguments, instead the indices are returned as a separate list so you can later iterate and create them manually. It happens, that even if you do not add an Index to the Table() arguments, the metadata already knows about all indices for that table (as Index is created for a specific table) and will create that index anyways. So delaying just did not work.

)
self.db.insert(table, select=sql_select)
if key is None:
Expand Down
26 changes: 24 additions & 2 deletions python/lsst/daf/butler/direct_query_driver/_sql_builders.py
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,8 @@
import sqlalchemy

from .. import ddl
from ..dimensions import DimensionGroup
from ..dimensions._group import SortedSequenceSet
from ..nonempty_mapping import NonemptyMapping
from ..queries import tree as qt
from ._postprocessing import Postprocessing
Expand Down Expand Up @@ -638,7 +640,7 @@ def to_select_builder(


def make_table_spec(
columns: qt.ColumnSet, db: Database, postprocessing: Postprocessing | None
columns: qt.ColumnSet, db: Database, postprocessing: Postprocessing | None, *, make_indices: bool = False
) -> ddl.TableSpec:
"""Make a specification that can be used to create a table to store
this query's outputs.
Expand All @@ -652,18 +654,22 @@ def make_table_spec(
postprocessing : `Postprocessing`
Struct representing post-query processing in Python, which may
require additional columns in the query results.
make_indices : `bool`, optional
If `True` add indices for groups of columns.

Returns
-------
spec : `.ddl.TableSpec`
Table specification for this query's result columns (including
those from `postprocessing` and `SqlJoinsBuilder.special`).
"""
indices = _make_table_indices(columns.dimensions) if make_indices else []
results = ddl.TableSpec(
[
columns.get_column_spec(logical_table, field).to_sql_spec(name_shrinker=db.name_shrinker)
for logical_table, field in columns
]
],
indexes=indices,
)
if postprocessing:
for element in postprocessing.iter_missing(columns):
Expand All @@ -679,3 +685,19 @@ def make_table_spec(
ddl.FieldSpec(name=SqlSelectBuilder.EMPTY_COLUMNS_NAME, dtype=SqlSelectBuilder.EMPTY_COLUMNS_TYPE)
)
return results


def _make_table_indices(dimensions: DimensionGroup) -> list[ddl.IndexSpec]:

index_columns: list[SortedSequenceSet] = []
for dimension in dimensions.required:
minimal_group = dimensions.universe[dimension].minimal_group.required

for idx in range(len(index_columns)):
if index_columns[idx] <= minimal_group:
index_columns[idx] = minimal_group
break
else:
index_columns.append(minimal_group)

return [ddl.IndexSpec(*columns) for columns in index_columns]
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