Thank you for responding. Forgive me if I'm missing something, but if I have a writer and separate readers, why would I want to have to communicate ledger ids between them? More specifically, we have a series of writers writing to a write-ahead log and a separate set of readers that are consuming these ledgers to move them into long term storage and send them to queues / workflows to be processed. This means I have to keep the state about which ledgers are available, and which are closed, which seems to be a complete duplication of the state that is already in BK.
I'm not sure named ledgers are helpful in this situation, except that we could keep less state (perhaps a sequential id.) On Mon, Feb 4, 2013 at 1:27 PM, Sijie Guo <[email protected]> wrote: > > Hello, Whitney: > > please check the replies inline. > > On Mon, Feb 4, 2013 at 8:47 AM, Whitney Sorenson <[email protected]>wrote: > >> Hey all, >> >> A couple questions about running BK stand-alone: >> >> 1) If I call openLedgerNoRecovery am I blocking writes or not? What are >> the guarantees I lose - just ordering? Can I use this to essentially read / >> tail an active ledger? >> > > open a ledger using openLedgerNoRecovery doesn't block any writes to it. > And you don't lose the ordering guarantee. You could use it to read/tail an > active ledger, but please keep in mind that you need to call > #readLastConfirmed to catch up to the latest confirmed entries added by the > writer. And the entries you could read from an openLedgerNoRecovery ledger, > is just between 0 and last confirmed. > > you could check: > http://zookeeper.apache.org/bookkeeper/docs/r4.2.0/apidocs/org/apache/bookkeeper/client/BookKeeper.html#asyncOpenLedgerNoRecovery(long, > org.apache.bookkeeper.client.BookKeeper.DigestType, byte[], > org.apache.bookkeeper.client.AsyncCallback.OpenCallback, java.lang.Object) > > >> >> 2) How can I access BK's metadata so that I can determine a list of >> ledgers, and which ledgers are closed/open? It doesn't appear in the client >> documentation ( >> http://zookeeper.apache.org/bookkeeper/docs/r4.2.0/apidocs/org/apache/bookkeeper/client/) >> Is this not an intended operation? Are clients supposed to track ledger ids >> on their own (we are currently doing this but it seems suboptimal) >> >> > currently we don't expose the API for client. Is there any special case > you are considering? We'd happy to expose it if necessary. > > Since most of the cases are working in following styles: a *standby* > writer observes the *active* writer state, if the *active* writer failed, > the *standby* writer would take over the responsibility, closed the ledger > written by *active* writer, replayed the ledger and created a new ledger to > write new entries. For now, clients needs to track ledger ids on their end. > > There is one proposal working on providing *named* ledgers on top of > bookkeeper to ease user's experience tracking ledger ids. You could check : > https://issues.apache.org/jira/browse/BOOKKEEPER-220 . And we are under > discussion on whether to provide ledger name internally in bookkeeper for > metadata access concerns. We'd like to hear your feedback on the usage of > API and make it better. > > > >> Thank you; >> >> -Whitney Sorenson >> HubSpot >> >> >
