Skip to content

Use LAG for _prev_data #231

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
wants to merge 1 commit into
base: main
Choose a base branch
from
Draft

Use LAG for _prev_data #231

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
12 changes: 6 additions & 6 deletions pghistory/models.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -458,12 +458,12 @@ def _get_select(self, event_model):
) = self._get_context_clauses(event_model)

event_table = event_model._meta.db_table
prev_data_clause = f"""
(
SELECT row_to_json(_prev_event) FROM "{event_table}" _prev_event
WHERE _prev_event.pgh_obj_id = _event.pgh_obj_id
AND _prev_event.pgh_id < _event.pgh_id
ORDER BY _prev_event.pgh_id DESC LIMIT 1

# Use LAG window function instead of N+1 subquery for better performance
prev_data_clause = """
LAG(row_to_json(_event)) OVER (
PARTITION BY _event.pgh_obj_id
ORDER BY _event.pgh_id
) AS _prev_data
"""
pgh_obj_id_column_clause = "pgh_obj_id::TEXT"
Expand Down