Hi Ted, Thank you very much for the reply! I didn't receive the reply in my email but I found it in ZK dev mail thread. So I could not reply directly to the thread.
I really appreciate a reply from the original author of multi()! And your blog (A Tour of the Multi-update For Zookeeper) is very helpful with understanding of multi(). Your reply helps convince my team that it is a real transaction. Regarding my 2nd question, maybe I should have described a bit of our challenge. When we have a large number of ZK write requests that cause high ZK write QPS, ZK sessions are expired by ZK. And this affects the application's connection to ZK. We wonder if we could apply multi() to batch the ZK write requests to reduce ZK write QPS so ZK wouldn't expire sessions. So in this case, do you think we could still not apply multi() to achieve the purpose? Thank you, Ted!! On Mon, Jul 27, 2020 at 1:40 PM Huizhi Lu <ihuizh...@gmail.com> wrote: > Hi Zookeeper Devs, > > Hope this email finds you well! > > I am working on some stuff that needs ZK multi(). I would like to confirm a > few things about this API. > > 1. Is this a real transaction operation in ZK? My understanding is, it is a > real transaction. If I put 3 write operations in this transaction request, > these 3 write operations are committed in 1 transaction with the same zxid > and 1 proposal. Observers should either see all the updates or none of the > updates. Observers should not see partial updates, eg. only 1 of the 3 > updates. > Yes. The multi() is atomic. It will happen or not and the program invoking the operation will be told why or why not. 2. We have a case to write multiple znodes. Currently it is sending the > requests one by one. With transaction, I believe we could batch writes in 1 > transaction request. This is intended to reduce ZK write pressure. Eg. we > are writing 100 znodes, putting it in one transaction request would reduce > write requests from 100 (single write request using create() or set()) to 1 > write request (transaction), right? And does this reduce ZK server write > request pressure? > Not really. The way that multi() works is that it does a group commit. There may be some economies in terms of number of network exchanges, but the internal work of testing whether the operations will succeed is the same. The point of multi() is to make use of and provide nuanced control over the normal group commit that Zookeeper is doing anyway. It should not generally be viewed as an efficiency improvement. Hopefully this helps. On Mon, Jul 27, 2020 at 1:23 PM Huizhi Lu <ihuizh...@gmail.com> wrote: > Hi Zookeeper Devs, > > Hope this email finds you well! > > I am working on some stuff that needs ZK multi(). I would like to confirm > a few things about this API. > > 1. Is this a real transaction operation in ZK? My understanding is, it is > a real transaction. If I put 3 write operations in this transaction > request, these 3 write operations are committed in 1 transaction with the > same zxid and 1 proposal. Observers should either see all the updates or > none of the updates. Observers should not see partial updates, eg. only 1 > of the 3 updates. > > 2. We have a case to write multiple znodes. Currently it is sending the > requests one by one. With transaction, I believe we could batch writes in 1 > transaction request. This is intended to reduce ZK write pressure. Eg. we > are writing 100 znodes, putting it in one transaction request would reduce > write requests from 100 (single write request using create() or set()) to 1 > write request (transaction), right? And does this reduce ZK server write > request pressure? > > Could you help explain? I am looking forward to your reply. Thank you very > much! > > Best, > -Huizhi >
