Let me take a step back and explain how I am looking at this from a high-level design viewpoint
Bookkeeper (BK) is like an LSM implementation of a KV store. Writes to all keys are appended to a single file; deletes are logical. Compaction reclaims space. An Index is used locate entries, tracking logical deletes and reclaim space. The index in BK is another LSM. Again, writes are appended, deletes are logical, and an index is used to locate entries , account for deletes and compaction to reclaim space (the implementation within rocksdb is far more complex with bloom filters and memtables, but you get the idea ) BK just uses a sophisticated index (rocksdb) which is tiny and cacheable and rocksdb has within it a sophisticated index which is small and cacheable So when I look at this proposal, what I see is the same - another attempt to build an LSM with a sophisticated index/cache mechanism using log structured storage. So I am quite skeptical that this needs to solved this way, within Pulsar. Joe On Wed, Jan 20, 2021 at 12:30 AM linlin <lin...@apache.org> wrote: > We can look at ManagedCursorImpl.buildIndividualDeletedMessageRanges > > What is saved in the entry is not a bitSet, but a messageRange one by one, > which contains information such as ledgerId and entryId. BitSet only exists > in the memory and is used to quickly determine whether it already exists. > In addition, the position of each ack will be stored in the > individualDeletedMessages queue. When persisted to the entry, the queue > will be traversed, and the position information of each ack will generate a > messageRange. > A messageRange contains lowerEndpoint (ledgerId+entryId), upperEndpoint > (ledgerId+entryId), 4 longs, about 256 bits. > > We assume a more extreme scenario, 300K messages, every other ack has an > unacknowledged, that is, 150K location information will be stored in > individualDeletedMessages. 150K * 256/8/1024 /1024 ≈ 4.6MB > Of course, there are also scenarios where the customer's ack spans several > ledgers. > > > On 2021/01/20 00:38:47, Joe F <j...@gmail.com> wrote: > > I have a simpler question. Just storing the message-ids raw will fit > ~300K> > > entries in one ledger entry. With the bitmap changes, we can store a> > > couple of million within one 5MB ledger entry. So can you tell us what> > > numbers of unacked messages are creating a problem? What exactly are > the> > > issues you face, and at what numbers of unacked messages/memory use etc?> > > > > I have my own concerns about this proposal, but I would like to > understand> > > the problem first> > > > > Joe> > > > > On Sun, Jan 17, 2021 at 10:16 PM Sijie Guo <gu...@gmail.com> wrote:> > > > > > Hi Lin,> > > >> > > > Thanks you and Penghui for drafting this! We have seen a lot of pain > points> > > > of `managedLedgerMaxUnackedRangesToPersist` when enabling delayed > messages.> > > > Glad that you and Penghui are spending time on resolving this!> > > >> > > > Overall the proposal looks good. But I have a couple of questions about > the> > > > proposal.> > > >> > > > 1. What happens if the broker fails to write the entry marker? For > example,> > > > at t0, the broker flushes dirty pages and successfully writes an entry> > > > marker. At t1, the broker tries to flushes dirty pages but failed to > write> > > > the new entry marker. How can you recover the entry marker?> > > >> > > > 2. When a broker crashes and recovers the managed ledger, the cursor> > > > ledger is not writable anymore. Are you going to create a new cursor > ledger> > > > and copy all the entries from the old cursor ledger to the new one?> > > >> > > > It would be good if you can clarify these two questions.> > > >> > > > - Sijie> > > >> > > > On Sun, Jan 17, 2021 at 9:48 PM linlin <li...@apache.org> wrote:> > > >> > > > > Hi, community:> > > > > Recently we encountered some problems when using individual> > > > > acknowledgments, such as:> > > > > when the amount of acknowledgment is large, entry writing fails; a > large> > > > > amount of cache causes OOM, etc.> > > > > So I drafted a PIP in `> > > > >> > > > >> > > > > > https://docs.google.com/document/d/1uQtyb8t6X04v2vrSrdGWLFkuCkBcGYZbqK8XsVJ4qkU/edit?usp=sharing` > <https://docs.google.com/document/d/1uQtyb8t6X04v2vrSrdGWLFkuCkBcGYZbqK8XsVJ4qkU/edit?usp=sharing> > > > > > > < > > https://docs.google.com/document/d/1uQtyb8t6X04v2vrSrdGWLFkuCkBcGYZbqK8XsVJ4qkU/edit?usp=sharing > >> > > > > > <> > > > > > https://docs.google.com/document/d/1uQtyb8t6X04v2vrSrdGWLFkuCkBcGYZbqK8XsVJ4qkU/edit?usp=sharing > > > > > > >> > > > > ,> > > > > any voice is welcomed.> > > > >> > > >> > > >
