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 > > > > > > > > > >
