> The goal is to start from a known MessageId and read the N message > before this MessageId.
Have you looked at the seek implementation to see if it would be feasible to extend the implementation and add a method to "seekBefore" a message id in the way you described? I haven't considered all of the implications, but if the main goal is to move the cursor, I think the solution should be about moving the cursor, not about reading a topic in reverse. Thanks, Michael On Tue, Mar 7, 2023 at 6:50 AM Alexandre DUVAL <kanna...@gmail.com> wrote: > > Hi Yong, > > The goal is to start from a known MessageId and read the N message > before this MessageId. > > Best, > > Kannar > > > On 3/7/23 01:53, Yong Zhang wrote: > > Hi Kannar, > > > > Just interested in what exactly your case. > > > > Why do you need to read messages in a reversed order? What is your case? > > > > Best, > > Yong > > > > On Mon, 6 Mar 2023 at 23:37, Alexandre DUVAL<kanna...@gmail.com> wrote: > > > >> Hi, > >> > >> I'm wondering if it is possible to introduce a new feature on Pulsar > >> which will enable users to read topic from a defined MessageId to > >> previous messages until the begin of the topic. > >> > >> I tried to use Pulsar SQL but it requires so much RAM even for little > >> queries (due to Presto design). > >> > >> Currently, every read in Pulsar are expected to be going forward. So it > >> might be a bit tricky to prevent every weird behavior by introducing the > >> feature. > >> > >> I'm currently tried to make an MVP/POC by introducting a readReverse > >> field in the CommandSubscribe that is used by ReaderAPI and currently > >> looking for to create a getFirstMessageId() on ManagedLedger > >> (https://github.com/CleverCloud/pulsar/pull/3). I also removed > >> startPosition < endPosition sanity checks in BookKeeper locally > >> (https://github.com/CleverCloud/bookkeeper/pull/2). > >> > >> We definitely prefer a readPrevious(), hasPreviousMessageAvailable() in > >> the ReaderAPI. > >> > >> I'm not familiar with these internals such as NonDurableCursor, > >> RangeEntryCache, ManagedCursor so it's a bit tricky. > >> > >> So I wondering someone to help/guide me or even directly handle the > >> subject (or the discuss). > >> > >> Regards, > >> > >> Kannar > >> > >> > >> > -- > *Alexandre DUVAL* > @KannarFR > /+33 6 12 97 19 70/
