Reload a window

Some tables keep changing for a while after their rows are written, and hold future dates: orders that ship later, deliveries scheduled up to two weeks ahead, bookings. A fixed window around today, replaced on every run, keeps them right without reloading the whole table. This guide reloads from 7 days ago to 7 days ahead.

Set the window

[sources.app.tables."public.deliveries"]
description = "Deliveries, one row per delivery, scheduled up to two weeks ahead."
write_strategy = "delete_insert"
cursor_column = "delivery_date"
lookback = "7d"
lookahead = "7d"
lookback_from = "now"

Setting	Here
write_strategy = "delete_insert"	Deletes the rows in the window it read, then inserts what it read. It needs a cursor_column and no key.
cursor_column	The date or timestamp the window is on.
lookback	How far back the window starts.
lookback_from = "now"	Count lookback back from the time of the run, not from the destination’s maximum. Needs a lookback.
lookahead	Read only cursor values before now plus this. A date cursor reads up to and including today plus that many days.

plan shows the window on the table’s cursor line. On 9 November 2026:

$ sqlload plan
…
Loads (1)                                           sqlload load
└── app__deliveries                                 delete_insert (cursor: delivery_date)
    ├── source  postgres  app  public.deliveries
    ├── route   read as Arrow -> DuckDB takes Arrow
    ├── batch   one commit for the whole read (committing part of an unordered cursor read could skip rows)
    └── cursor  delivery_date from 2026-11-02 (now minus lookback 7days), below 2026-11-17 (now plus lookahead 7days)

Every run reads delivery_date from 2 November up to and including 16 November, deletes those dates from the destination, and inserts what it read. A delivery deleted at the source while its date is in the window is deleted from the destination too.

How the window is counted

• Days are counted in UTC. A date cursor moves by whole days.

• A timestamp cursor reads from exactly now minus lookback to now plus lookahead.

• The first run reads the same window, so rows before it never load. To fill the table first, run --reload once (below), or backfill a range.

• --start-cursor and --end-cursor replace the window for one run:

  $ sqlload plan --start-cursor 2026-10-01 --end-cursor 2026-11-01
  …
      └── cursor  delivery_date from 2026-10-01 (--start-cursor), below 2026-11-01 (--end-cursor)

• --reload rebuilds the table from cursor_start, or from the first row, up to the lookahead:

  $ sqlload load --reload --yes
  …
      └── cursor  delivery_date reload, everything, below 2026-11-17 (now plus lookahead 7days)

Without lookback_from

Without lookback_from = "now", lookback counts back from the destination’s maximum of the cursor. Each run then re-reads a window behind the newest row it already has, such as the last 2 hours, and everything after it:

[sources.app.tables."public.page_views"]
description = "Page views, one row per view."
write_strategy = "delete_insert"
cursor_column = "viewed_at"
lookback = "2h"

That suits rows that arrive late, but not a table holding future dates: its maximum is already ahead of today. lookahead works with either, and caps the read at now plus the lookahead.

Limits

• lookahead and lookback_from = "now" need a date or timestamp cursor.
• append takes no lookback, which would insert the window again on every run. Use delete_insert, or merge when the table has a key.
• A files target takes neither lookahead nor lookback_from = "now": its window follows its newest partition.
• Python tables take lookback, but not lookahead or lookback_from.

See Cursors and state for how a run decides where to read, and delete_insert for how it replaces a range.