In this commit for example I can see that the sort of messages is being made inside the client
What if we have a chat with something like 50k+ messages? And this sort happens at every new signal? And this implies that pagination is not a feature of RSM yet?
see if you can do what you need with granularity of Path rather than pagination
path trees represent a more general approach than āpageā
see this conversation for an example - https://forum.holochain.org/t/how-to-structure-implement-a-sorted-linked-list-on-the-dht/4478/12
Oops! Looks like Iād have to make that conversation public,
Give me a min.
Quoting David,
So you can sort-of have your DNA programmed such that messages follow a time-ordered BST (Binary Search Tree) branch (not the whole tree, just a branch, or you may call it a linked-list; https://appliedgo.net/media/balancedtree/BinTreeShapes.png).
So for a simple scenario, the full-parsed-path may look like this:
public_posts.post_xxx(the-entry-hash-of-the-post-youāre-interested-in-reading).messages.msg_xxx(the-entry-hash-of-the-latest-message; if you follow the hash, youāll find the message āThank you so much; issue resolvedā).msg_xxx(the-previous-post; follow to discover āTry rebooting the systemā)ā¦ and so onā¦
It works great for messages, 'cause youāre mostly interested in the latest messages and donāt have to follow a long trail just to read the latest ones. Linking a new post is trivial; only takes a few calls to create_link() and delete_link(). Moreover, it mimics the order in which messenger clients have to call get_previous_message() when the user keeps scrolling up to reach and read some arbitrarily old message.
However, I generally donāt like using the pure-path method in which the full-traversed-path may look like:
public-posts.Windows-10-broke-again.messages.Thank-you-so-much.Try-rebooting.
Though I prefer the linked-list workaround hack.
Anyways, thatās all I have to addā¦
blogs pretty commonly create urls like posts/2020/01/06/my-blog-post and a similar thing happens for the media files they save on the file system to prevent the scenario where you end up with 50k images in a single directory
Path tackles two problems:
the first is solved by just doing something with hashes but the second needs something domain specific
examples:
2020.01.07
the limitation of pagination is that you need to page over some field
https://developer.twitter.com/en/docs/twitter-api/v1/tweets/timelines/guides/working-with-timelines
e.g. twitter uses since_id
so the question for me is that after you solve the hot spot problem, which implies data is being spread across many agents, how would āpagesā be created
This post is still 404āing for me. Can you guys open it up? Id love to take a look.
which post?
This one:
https://forum.holochain.org/t/how-to-structure-implement-a-sorted-linked-list-on-the-dht/4478/12
aaah, that is because it was a private message that i thought was a public forum thread haha
Hahha, np just grant me a cap token to view the thread 
done. (would do all talks publicly now onā¦ :-))
Sorting the data ad-hoc at the client is a terrible idea; it may work in the short term, but beyond that, for any real-world use-case, Iād highly recommend against itā¦
what is āthe clientā where there are no servers?
someone needs to do the sorting, if you foist off heavy sorting āto the DHTā then someone is going to be asking you to do the same at some point for them.
try to create some bounds on how much data youāre sorting at once by building granularity into large sets of data - https://docs.rs/hdk/0.0.100-alpha.1/hdk/hash_path/index.html
even better, try to include rough ordering into the granularity itself
The client in the sense that the UI consumes the DNA, so it is in essence a client to the DNA. Of course, thereāre no client and servers, but what better name to give to the UI (PWA, SPA, electron app, a windows binary, or simply a CLI interface) than a client.
what is the main concern re: sorting in the UI vs. the wasm?
At https://docs.rs/hdk/0.0.100-alpha.1/hdk/hash_path/index.html,
- Holochain neighbourhoods (who needs to hold the data) center around the content address so the poor nodes closest to āchat-messagesā will be forced to hold all messages (DHT hotspots)
Needs correction.
It should rather say,
āthe poor nodes closest to āchat-messagesā will be forced to hold the links to all messagesā
They wonāt be storing all messages, obviously! If that were the case, weād be calling it a āfatspotā.
It is a hotspot in the sense that almost all users trying to read messages will have to do so through the āall-messagesā entry, i.e., all users would, all day long, be calling the get-links on that one single entry (the āanchorā entry that simply says āall-messagesā).
Correct me if Iām wrong though (in which case it would mean that Iāve been wrong all this timeā¦ :ā(
[Indeed, one can argue that holding the links (i.e., the hashes plus some Holochain link-related data) to all messages is kinda like the same as holding all entries themselves, especially from a storage-perspective, and I agreeā¦ It indeed is a hell of a bulk load; but itās not the same as holding all the entries themselves.]
Will be waiting the next noonā¦ My technical doubts regarding your tree vs a linked-list approach is all thatās remaining to be sortedā¦ Would love to finally have that clarified too.
Ideally the tree structure embeds some domain specific granularity
Examples of granularity include:
- Orders of magnitude
try to find a way to create buckets of granularity
(That way) we never need to fetch all messages because we can start as deeply down the tree as is appropriate
I get it. Makes perfect sense.
Imagine a clutter-twitter app, where people post tweets, and users should be able to see the latest tweets. It has no concept of Profiles or whatever. Everyone kinda posts in a universal feed.
Given a tree-based (āPathā-based, in HDKās terminology) solution, users who want to read last hourās posts can simply retrieve the entry for ā1/3/2021: 23.00 to 24.00ā and simply do a get-all-links on it and get all the messages posted in that hour (assuming the granularity of partitioning/pagination is 1 hour).
But the problem is that not all use-cases that the end-developers ((h)app developers) have exhibit that sort of a granularity; they simply donāt fit in that domain. Thus, the tree-style solution fails them (as it once failed me)ā¦
Imagine that fresh Ford Model 1 cars are on sale, and that buyers would have to purchase it in exchange for US Dollars. And, for this specific use-case, imagine that no single manufacturer is churning out those cars; rather people who have a 3D-printer are printing those cars (at home) and offering it for sale at an arbitrary price that they think there hard-work is worth for; this transaction has to take place on a Holochain app (Yippee!!!).
Hereās the catch: the user has absolutely no idea what a Ford Model 1 should be worth.
One can see that a tree-based solution wonāt be of any help hereā¦ For example, you may store āall-cars-for-dollarsā entry, and link them to āall-cars-for-0-to-100-dollarsā, āall-cars-for-100-to-200-dollarsā, āall-cars-for-500-to-600-dollarsā and so onā¦ Further down, one may have other subtree-roots that say āall-cars-for-100-to-150-dollarsā and so onā¦
Now what can you, as a rational user, query to this (h)app so as to strike the best deal? Nothing! Youāre absolutely hopeless due to such an architectureā¦
You can make a guess and search for the subtree-root (i.e., an entry) that says āall-cars-for-0-to-100ā, in which case youād just be right on the money (meaning very lucky). But what if those 3D printers costed a billion dollars each? Well then would forever be searching in the wrong places! Plus doing a get-all-links to the rootest-root isnāt an option ('cause what would be the point then; I mean, that way weād be back to the same problem we started with!)
Imagine another architecture of organizing such diverse prices on the DHT.
Thereās an entry that says ābest-dealā, to which is linked the Ford Model 1 thatās up for sale for the least amount of money. That car (or rather, the entry of that car) further links to the next best deal, and so onā¦
The user gets() the ābest-dealā entry, gets its link (tagged ānextā), and guess what? Heās found the cheapest Ford Model 1!
[Replace Ford Model 1 with, letās say, Starbucks coffee-coupons, and US Dollars with Amazon-coupons and youāve got the Vrilās token exchange system. Just so as a side-noteā¦]
[Note that for this use-case, new sellers might have to be placed anywhere within the listā¦ However, for the use case of messages, this is a great approach; in fact, Iād say even better than HDK::Path based approach. The āLatest-Messageā entry would, upon the arrival (i.e., the posting) of a new message, would simply delete the previous link that it held, and rather create a new one that points to this newer message, while the new message would now (and forever from then on) hold the link of the last latest message (the previous latest message, in other words). This way, a user can read the latest message, the one posted before it, the one posted before that one, and so onā¦ Trust me, nobody reads the messages posted on āTuesday, July 21st 2019ā; they simply scroll up and up until they reach what they had been looking for. And my experience with distributed databased has taught me to always āstore data the way it would be retrievedā, i.e. time-sorted ālatest-firstā manner, in this example.
One doubt I have is whether deleting and creating (or simply updating, as updates are nothing but sequential deletes and creates) the link on the ālatest-messageā entry would be an efficient thing to do, especially from a storage perspective. Because there would always be some remnant leftovers (such as the link-headers, etc)ā¦ But, from a storage-optimization perspective, your Tree solution also ends up creating a great many ārootsā and āsub-rootsā, such as āall-cars-for-0-to-100-dollarsā which do not hold any valuable information in and of themselvesā¦ Plus, youāve already assured me that itās best to ignore such silly storage-costs (How exactly does holochain support micro-payments?).
As for the hotspot thing, then yeah, I would mostly be hitting the ālatest-messages-between-the-a-man-and-davidā entry (substitute the string with a well-formatted chat-room entry that stores the hashes of the participants and not their names; you get the ideaā¦) because thatās what I care about (i.e., I care about the latest messages). But note that it always has just one link. Plus it (or rather, the neighbourhood of that entry) would only be receiving get() requests from me and you; not that hot a spot. Even if the whole world were in that room, the same argument would apply to, letās say, a famous personās tweet/message when everyone wants to read it at the same time (i.e., would incur a huge traffic influx on that neighbourhood, so as to make their deviceās wifi glow red hot).
Interesting points, althought I think the linked list approach has too many issues to be really viable.
So, from write costs: every action (create_link, create_entry, delete_entryā¦) creates a number of DhtOps (1 DHT OP = 1 thing that has to change in the DHT). Doing too many of these is bad not so much because of storage, but because of gossip and processing. You need to be gossiping at all times with your neighborhood to guarantee that all DHTOps stay online, and recruit new nodes if that doesnāt look likely. Those new nodes are going to need to validate itā¦ Quite a bit of background processing. Here is how many DHTOps every action creates:
create_entry: 3update_entry: 5delete_entry: 3create_link: 3So yes, be careful when deleting things away. Also, they are not really deleted and cleaned away from the DHT, they are kept there for integrity and only āmarked deletedā. So you actually gain no storage benefit.
Also, nodes or entries cannot really āreactā to an DHTOp being validated and held in the DHT by themselves, it has to be one of the agents who actively takes and action after that happens. Youād have problems otherwiseā¦ Which of the 25 nodes holding the entry executes the action? How do validation rules work in that sense? What about partitionsā¦?
About the querying of the linked listā¦ How are they going to maintain order? Letās say that the cheapest one is $50, and I have to commit one with $100: do I need to go over the whole list just to find the one I need to link from? What if just then the $50 one is deleted? What if two people commit two different $50 at the same time, or while being in different partitions?
While interesting and maybe useful in specific cases, in general I think this kind of approach does not really play well with the CRDT behaviour in holochain IMO, in which the data structure doesnāt depend on the āorder of arrivalā of events.
Another thing is that the UI may very well obscure the details of querying for paths. I think itās been already 3 projects in which we are doing time indexing via trees of paths, and I think only one of them had explicit time range filter, the other were just infite-scrolling UX patterns like the ones you are describing.