Can you grant me the permissions for editing the wiki page? - Gerrit
On Thu, Nov 17, 2016 at 1:37 AM, Gerrit Sundaram <gerritsunda...@gmail.com> wrote: > > > On Tue, Nov 15, 2016 at 2:14 AM, Sijie Guo <si...@apache.org> wrote: > >> On Sat, Nov 12, 2016 at 2:30 AM, Gerrit Sundaram < >> gerritsunda...@gmail.com> >> wrote: >> >> > On Fri, Nov 11, 2016 at 1:09 PM, Sijie Guo <si...@apache.org> wrote: >> > >> > > I liked this topic. A better name might be 'stream storage >> primitives', >> > as >> > > we treat DL as a stream storage. Comments inline. >> > > >> > > On Wed, Nov 9, 2016 at 3:09 AM, Gerrit Sundaram < >> > gerritsunda...@gmail.com> >> > > wrote: >> > > >> > > > As what Sijie suggested in the other email thread, I started this >> email >> > > > thread for discussing the stream operation primitives. >> > > > >> > > > The stream operations that I am aware of that DL supports are >> > > > >> > > > * Open a distributedlog stream >> > > > * Delete a distributedlog stream >> > > > * List all the distributedlog streams under a namespace >> > > > >> > > >> > > Are you also looking for listing streams under a 'sub-namespace' - (or >> > > streams have common prefix)? (Based on my understanding on your >> proposal, >> > > you might need this for a filesystem-like API?) >> > > >> > >> > Yes. However it seems like DL is more designed with flat namespace with >> > just streams. >> >> >> Ah, yes. The original thought is to tight a namespace to a user or an >> application. Under a namespace, application can manage the streams by >> their >> own. So that's why it was designed with a flat namespace. >> >> >> > There is no concept about 'sub-namespace'. Although I >> > probably can hack it by just naming the stream names in a filesystem >> > path-like way. >> > >> > However I am still curious do you guys want to introduce any sort of >> naming >> > hierarchy in the naming within a namespace. For example, can you have a >> > 'StreamSet', which is a set of streams? (like in filesystem, a directory >> > has a list of children). If you have similar hierarchical, it definitely >> > will simply my work. >> > >> >> In the write proxy, we have a similar concept like 'StreamSet' to group >> some physical DL streams into one virtual stream. However that was mostly >> used for exporting metrics for grouped virtual streams. We don't quite >> emphasize the concept of 'virtual stream' in DL. As we tended to let the >> application decide what the virtual stream looks like. >> >> However, for metadata organization and management, it might make sense to >> think of such hierarchy. >> >> What do you have in your mind about 'StreamSet'? Can you explain a little >> more? > > > I was thinking a group of streams that might be used for same application > but store different parts of data. It is like the 'virtual' stream that you > mentioned. > > - Gerrit > > >> >> > >> > >> > > >> > > >> > > > * Seal a distributedlog stream >> > > > * Truncate a distributedlog stream >> > > > >> > > >> > > Just to clarify this, the 'truncate' in DL is to trim the head of the >> > > stream not the tail. >> > > The 'truncate' in filesystem world is to a size of precisely *length* >> > > bytes, it is truncating the tail. >> > > >> > > Make sure we clarified it and are on same page. >> > > >> > >> > Yes, we are on the same page. >> > >> > >> > > >> > > >> > > > >> > > > I am looking for a more filesystem-like API. for example, >> > > > >> > > > * Get the status/attributes of a stream (like stat in filesystem) >> > > > >> > > >> > > +1 for stream status/attributes. I think we might actually already >> have >> > > this in DL. since in kestrel, we use that for storing customized >> > metadata. >> > > It might make sense to formalize it into 'stream status'. >> > > >> > >> > Gotcha. >> > >> > >> > > >> > > >> > > > * Rename a stream >> > > > >> > > >> > > we've talked about this for a while. +1. >> > > >> > > >> > > > * Symlink a stream >> > > >> > > >> > > Symlink a stream is probably easy to do. +1 we've thought about that >> for >> > > having the flexibility to move stream between different storage >> backend. >> > > Symlink would help this. >> > > >> > > But a more fundamental thought here is symlinks for log segments. So >> > when a >> > > symlinked stream is deleted, the underneath log segments might not be >> > > deleted until its link count decreased to zero. >> > > >> > > >> > > >> > > > >> > > > Another operations that I can think of might be useful. >> > > > >> > > > * Split/Fork a stream (it can be useful for dynamic data >> partitioning) >> > > > >> > > >> > > >> > > >> > > Split and fork a stream sounds interesting. But it sounds like a more >> > > high-level feature rather than storage primitives. Actually, it might >> be >> > a >> > > good separate discussion feature. >> > > >> > > >> > > >> > > >> > > > * Merge/Concat streams >> > > > >> > > >> > > >> > > I think there is already one outstanding jira for concatenating two DL >> > > streams. Jia and Arvind are working on that. >> > > >> > > https://issues.apache.org/jira/browse/DL-46 >> > >> > >> > I will watch that lira. >> > >> > >> > > >> > > >> > > >> > > >> > > > >> > > > The above operations are based on my knowledge about DL. Feel free >> to >> > add >> > > > more. >> > > >> > > >> > > > >> > > > - Gerrit >> > > > >> > > >> > >> > >
