get_delta_channel_history(
self,
*,
config: RunnableConfig,
channels: Sequence[str]
) -> Fast-path override of BaseCheckpointSaver.get_delta_channel_history.
Two-stage query, both stages cover ALL requested channels:
Stage 1 (paged): dynamic SELECT over checkpoints with K parallel
JSONB key lookups (one column pair per channel) — no subquery, no
aggregation. Pages newest-first by checkpoint_id with a cursor;
page size is _DELTA_PAGE_SIZE. Stops paging when every channel
has found its seed or the chain is exhausted.
Stage 2 (per-channel UNION ALL): one branch per channel reading
checkpoint_writes filtered to that channel's specific
chain_cids, plus one branch per channel that has a seed reading
checkpoint_blobs for that channel + version. Avoids the
over-fetch of a single channel = ANY(channels) filter when
channels have different chain depths.