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 three
columns per channel: its version, an EXISTS probe for a stored
blob at that version, and its inline value. Pages newest-first by
checkpoint_id, starting at the target; page size is
_DELTA_PAGE_SIZE.
Stops paging when every channel has found its seed or a page comes
back short.
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.
get_delta_channel_history(
self,
*,
config: RunnableConfig,
channels: Sequence[str]
) -> Mapping[str, DeltaChannelHistory]