[DB-1625] Indexing without sequences (suggestions) #5238
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…scribing to a position but the position is not yet available in the stream/log. In that case the subscriptions will go live directly and wait - there are no retries involved
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…reading them: * If in-flight records are committed/cleared while reading them, stop where we have reached and return a partial result. * Always read in-flight records before reading database records: * If in-flight records are committed while reading, we can be sure that they will be present in the subsequent query of database records. * After we've read the database records, some of them may overlap with in-flight records: deduplicate the result. * Simplify inclusive/exclusive log position queries * Simplify sorting by RowId: Always sort in ascending order (return negative RowIds for backwards database reads)
…es event by event, not transaction by transaction (Using only the `PreparePosition` means that the checkpoint could move backwards when processing events from an explicit transaction)
…dditional complexity. There were some issues with the implementation: * "" ($all) was being passed as the index name to SubscriptionMessage.PollStream * The position being polled was incorrect (it was using the main index's position instead of the secondary index's position) * Long polls are not suitable for backward index reads - only forward reads * MissedEvents: the lastIndexedPosition is the main index's position, not the secondary index's position
* cosmetic fixes * don't exclude first event when subscribing to the beginning of the index
…n reached (instead of potentially reading an extra page)
- Throw ObjectDisposedException when disposed - Use the prepare/commit positions from resolvedEvent.OriginalPosition - Track the stream index processor's commit time as part of the commit time
- Separate initialization of the last appended record to avoid the need for synchronization. If the last event in the log was a system event, it was also previously filtered out by RecordAppended() - Use the commit position instead of prepare position of events
…tion when reading events This is required as prepares written with explicit transactions will not have an expected version set - the event number is derived from the commit record.
- Clear in-flight records after flushing the appender to make sure that concurrent reads will see the record either in the in-flight records or in the database
The data in the secondary indexes is already committed to a quorum number of nodes, so it might be ok. But it might be risky, as disposal could be happening due to a fatal error. for e.g consider the case where the system ran out of disk space: we are trying to write even more data.
…irectory by default: - Indexes are usually stored on a separate disk so that IOPS are not shared with the DB for better performance - It's better if DuckDB related files (like the write-ahead log, etc.) are stored in its own directory so that the database code doesn't accidentally modify them. (for e.g all .tmp files are deleted on startup)
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