Good day, Cole. Glad to exchange more ideas with you in this thread.
>I think it would make sense for TinkerPop to adopt a default language for the >new match step, which is some heavily restricted form of GQL (read-only, >limited to basic MATCH, WHERE, and RETURN statements). This "standard" >language could then be used in the new match step without a language >with-modulator. Providers would still be free to support their own languages >via that modulator if they choose. That makes sense, I agree with you. It would be even better, IMHO, if the TP project added an ANTLR4 parser for GQL match statements (there is already at least one ANTLR spec in the public domain) that vendors can use to work on the AST level. We can talk about possible collaboration on this task. > I'd be interested if you have any examples where embedded parameters present > a clear advantage. I expected that this question would be raised :-) But decided to move the discussion to a follow-up thread to avoid polluting the main proposal. Except for obvious query injection cases, which, in the absence of query parameters, should be handled by users themselves, another important argument for the presence of query parameters is that query parsing is quite a heavy process, and the consumption of 20% of CPU resources on query parsing is not a rare exception. To avoid this overhead, query parsing results (likely ASTs) are cached by a simple string hash code (likely the only way, as they are not parsed in this phase). Of course, the absence of query parameters very often increases the variability of queries by several orders of magnitude and voids caching efforts. >I would prefer to solve that problem at the broader gremlin level, instead of >isolating it to the match step. Would you happen to have any other applications in mind? > I will take some time next week to work through some example queries and get > a better sense of how I feel on each option here. Looking forward to reading your conclusions. >. I think that all "variables" bound in the match query should be stored such >that they are later selectable. Yeah, cool idea! >Overall I think this would be a great change to gremlin. I look forward to >keeping this discussion going and ultimately seeing the changes land in >TinkerPop. Thank you, Cole! Once the discussion comes to a natural conclusion, I will summarize all the ideas again to ensure that we are all on the same page. Then, we will add it to our roadmap. On Sat, Aug 23, 2025 at 12:01 AM Cole Greer <[email protected]> wrote: > > Hi Andrii, > > Thanks for starting this discussion and putting together this proposal. I > want to start by saying that overall, I'm massively in favour of the proposed > overhaul of match(). This is a topic that has come up many times in the past, > and taking advantage of an established declarative language like GQL always > seems to be the preferred solution. > > The idea of having the language configurable via something like > `.with(“language”, > “GQL”)` is quite interesting, and something I haven't seen in previous > discussions. There is clear value in allowing providers to support their own > preferred declarative languages here, but I also worry about the loss of > query portability if TinkerPop is too hands off on the choice of declarative > language. I believe the vast majority of usages here will be seeing a > traversal with a simple GQL-like match pattern. I think it would make sense > for TinkerPop to adopt a default language for the new match step, which is > some heavily restricted form of GQL (read-only, limited to basic MATCH, > WHERE, and RETURN statements). This "standard" language could then be used in > the new match step without a language with-modulator. Providers would still > be free to support their own languages via that modulator if they choose. > > I will take a bit more time to consider the withParameter() proposal. My > initial reaction is that I prefer to tie it into the existing parameter > bindings included in remote requests to gremlin-server. I would like query > parameters to function in a unified manner across the entire traversal if > possible, instead of a separate detached system isolated to the new match > step. I understand the current limitation of only supporting parameters in > remote traversals. I'm not immediately seeing the need to support parameters > for embedded traversals here, I'd be interested if you have any examples > where embedded parameters present a clear advantage. If we do decide there is > a need for embedded parameters, I would prefer to solve that problem at the > broader gremlin level, instead of isolating it to the match step. > > I totally agree that the start and mid-step behaviour of the new match step > should be modeled after V() and E(). > > I think the trickiest part of getting this right is the return types. The > most common use cases I expect is where the RETURN clause only includes a > single node or edge. In this case I completely agree with returning the > element itself. I definitely want to support usages such as g.match("MATCH > (n{name:'Cole'}) RETURN n").out()... My main tenet here is that results > should naturally flow from the declarative match into the subsequent gremlin > and be easy to consume. If multiple objects are returned, I would agree that > it is necessary to return a Map<String, ?> as in g.match("MATCH > (p:person)-[e:created]->(s:software) RETURN *") -> {"p": V[1], "e": E[9], > "s": V[3]} ... > > I'm still on the fence for how to handle single returns of non-elements. I > see the value in your recommendation to return a map of size 1, but I also > see some convenience to directly returning the value (usually a single > property). I will take some time next week to work through some example > queries and get a better sense of how I feel on each option here. > > There is one final item which I would like to see added to the proposal. I > think that all "variables" bound in the match query should be stored such > that they are later selectable. Essentially I think it's important to support > something like this: > > g.match("MATCH (n1{name:'Cole'})-[]->(n2) RETURN > n1").where(...)...select(n2).out()... > > The ability to select other bound variables later in the traversal should > greatly limit the number of times users are forced to return multiple items > at once, which reduces the amount of use cases where users will be forced to > break down maps in gremlin to complete their query. > > Overall I think this would be a great change to gremlin. I look forward to > keeping this discussion going and ultimately seeing the changes land in > TinkerPop. > > Thanks, > Cole > > On 2025/08/22 15:46:10 Andrii Lomakin wrote: > > Good day. > > > > I propose new semantics for the match step in Gremlin, which we discussed > > briefly in the Discord chat. The current ideas listed partially summarize > > ideas suggested by several discussion participants. > > > > The current semantics of the match step are complex to optimize, so users > > do not use this step in practice, and DB vendors do not recommend using > > match step in queries. > > > > Instead, what is proposed is to provide a new match step based on > > declarative semantics. > > > > Signature of this step is quite simple: Travervsal<S, E> match(String > > matchQuery). > > > > Where matchQuery is a match statement written in declarative query language > > supported by the provider, I will use GQL as an example below. > > > > This step will require the language as a configuration parameter provided > > using with the step. > > > > So the simplest query will look like: > > > > g.match(“MATCH (person:Person)-[:knows]->(friend:Person)”).with(“language”, > > “GQL”) > > > > match step can accept query parameters, so if we provide a query like > > g.match(“MATCH > > (p:Person WHERE p.name = $personName)RETURN p.email”).with(“language”, > > “GQL”) > > > > we may use parameter bindings, but it will work only for interaction with > > Gremlin Server, so instead, I propose an additional modulator step: > > withParameter(String > > name, Object value) > > > > In such case final version will look like: g.match(“MATCH (p:Person WHERE > > p.name = $personName) RETURN p.email”).with(“language”, > > “GQL”).withParameter(“personName”, “Stephen”) > > > > Alongside the version of withParameter step that provides the name of the > > query parameter, a version with the following signature should also be > > provided: withParameter(int index, Object value) for query languages that > > support indexed parameters with/instead of named parameters. > > > > Because we already introduced one modulator step, it is reasonable to > > consider replacing it with step by more specific withQueryLanguage() > > modulator step that will allow us to add more expressiveness to the > > resulting queries. > > > > In such case final version will look like: g.match(“MATCH (p:Person WHERE > > p.name = $personName) RETURN > > p.email”).withQueryLanguage(“GQL”).withParameter(“personName”, “Stephen”) > > > > As for the scope of application of this step, I recommend making it behave > > exactly as it is implemented for the V() and E() steps. It could be added > > in the middle of GraphTraversal, but the execution result will be the same > > pattern matching execution applied to the whole graph stored in the > > database (not to the item filtered/transformed by the previous steps). > > > > It also means that match step will be added to the GraphTraversalSource. > > > > As for the format of the output of the match step, I would recommend the > > following: > > > > 1. If the match statement returns an Element instance, it is returned as > > is. > > > > 2. Otherwise, it should return any value that is allowed to be a property > > value in Element. > > > > 3. I would add an optional recommendation to return either Element or > > Map<String, > > ?> where the key of the map is the result a projection of the query result > > which in case of query g.match(“MATCH (p:Person WHERE p.name = > > $personName) RETURN > > p.email”).withQueryLanguage(“GQL”).withParameter(“personName”, “Stephen”) > > > > will look like {“p.email”: “[email protected]”}. Following this optional > > recommendation will, IMHO, improve user experience. > > > > This step should be restricted to executing only idempotent queries. > > > > I would also recommend adding versions of withParameter() that accept > > Traversal as a value of the parameters, namely: > > 1. withParameter(String name, TraversalSource value) > > > > 2. withParameter(int index, TraversalSource value) > > > > > > > > The current version of the match step should be deprecated and then removed. > > > > I want to thank Stephen Mallette, whose initial idea closely aligned with > > ours and who actively contributed to our discussions. > > > > I'm looking forward to your thoughts, observations, and any other feedback > > you may have. > > > > Best Regards, > > YouTrackDB development lead > > Andrii Lomakin > >
