Materialises change-log rows from the events hot-store into the Feed database, using an independent change_seq cursor persisted in the feed DB. Implements events::IEventProjector so it can be driven by the existing EventsRuntime projection loop. More...

#include <feed_projector.hpp>

Inheritance diagram for dcn::feed::FeedProjector:

Public Member Functions
	FeedProjector (events::SQLiteHotStore &store, Feed &feed, const asio::strand< asio::io_context::executor_type > &write_strand, events::ProjectorRetryConfig retry={})
std::string_view	id () const override
std::int64_t	cursor () const override
asio::awaitable< std::size_t >	projectBatch (std::size_t limit, std::int64_t now_ms) override
Public Member Functions inherited from dcn::events::IEventProjector
virtual	~IEventProjector ()=default

Detailed Description

Materialises change-log rows from the events hot-store into the Feed database, using an independent change_seq cursor persisted in the feed DB. Implements events::IEventProjector so it can be driven by the existing EventsRuntime projection loop.

Cursor policy:

cursor is loaded from the Feed DB at construction (via Feed::getFeedCursor) and persisted after each successful batch (via Feed::setFeedCursor).

Failure policy (per applyChange):

on failure the cursor is left before the row and the row is retried on subsequent projectBatch passes, so transient failures (e.g. busy feed DB) heal on their own. After ProjectorRetryConfig::max_attempts consecutive failing passes the row is dead-lettered (FEED_DEAD_LETTER_BIT in the hot store) and the cursor advances past it: a permanently parked cursor would freeze the prune watermark for every projector and grow the hot store without bound. Dead-lettered rows are exempt from pruning, so no chain event data is lost; a periodic idle-time sweep (ProjectorRetryConfig::sweep_interval_ms) retries them and clears the bit once applyChange succeeds. If the dead-letter mark itself cannot be written, the cursor stays parked.

Constructor & Destructor Documentation

◆ FeedProjector()

dcn::feed::FeedProjector::FeedProjector	(	events::SQLiteHotStore &	store,
		Feed &	feed,
		const asio::strand< asio::io_context::executor_type > &	write_strand,
		events::ProjectorRetryConfig	retry = {} )