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A second live query over a refetched on-demand source keeps a short joined window

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Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
12/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
typescript
Ambito
data

Direzione di ricerca

The payload names no source files, so start from the ordered-work oracle in #2132 and replay seed 3103989100, which is pinned as an it.fails case. Find where the second live-query Collection's ordered loader decides whether to request more rows after a refetch. The fix is done when that replay passes, the it.fails marker is removed, and the refetching-provider plus second-Collection combination can return to the random grammar.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Problem

Two live-query Collections can read the same on-demand source. After a refetch, the second Collection can show a short ordered window. It stays short until a different change starts a load.

The ordered-work oracle in #2132 found this with a generated history. The failure also occurs with the production code on main, so #2132 does not cause it.

Minimal trace

  • On-demand source with a refetching provider. The provider sends no change until a refetch, and each refetch keeps every served ordered range whole.
  • Query: rows LEFT JOIN markers on the row's join key (link), WHERE the marker exists, ORDER BY rank ASC with an index on rank.
  • Collection A has limit 2. Collection B (the second live-query Collection) has limit 3.
  • Rows 9, 0 and 1 have rank 0 and a marker. Row 2 has rank 1 and no marker. 200 filler rows have rank 100 and up, with markers.

Steps:

  1. The backend inserts row 10, with rank 1 and no marker. The provider does not send it yet.
  2. Row 0 changes its join key, so it no longer matches a marker. The provider does not send this yet.
  3. The provider refetches.

Expected window of Collection B: ranks [0, 0, 100] (rows 9, 1 and the first filler row). Actual window: [0, 0]. Collection A shows the expected window.

Ingredients

The failure needs all of these:

  • A refetching provider. A forwarding provider passes.
  • A second live-query Collection on the same source. One Collection with limit 3 passes.
  • A join on the row's join key. The same history with marker changes passes.
  • A tie at the window boundary with a row that the provider never sent. Without the insert of row 10, the history passes.

A source filter instead of a joined filter also passes.

Hypothesis

After the refetch, row 0 leaves both windows in one commit. Collection B must load past the rank-1 tie group, where every row fails the join. Two causes are possible:

  • Collection B's ordered loader does not request again, because its last page has the same count and boundary as before.
  • The rows that Collection A already loaded answer the request of Collection B.

Then nothing proves the window, and no request follows.

Evidence

  • Witness trace: oracle seed 3103989100 of the ordered-work oracle in #2132. #2132 pins it as an it.fails replay, and excludes the refetching-provider and second-Collection combination from the random grammar until this fix.

This issue was written by Isaac.

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