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A comment on Ask HN: What was your experience using a graph database?.

Re:Ask HN: What was your experience using a graph database? by adamfeldman on Monday December 31, 2018 @01:54PM (#18796213)
What sort of problems are well-suited to graph databases? In other words, what are some scenarios where I will run into trouble using Postgres?

edit: I've previously looked into ArangoDB.com, Dgraph.io, JanusGraph.org, and Cayley.io (to run on top of CockroachDB). I understand all of these are scalable distributed systems, and Postgres is not (CitusData.com aside). Do the benefits of these other systems mainly come when you outgrow single-node Postgres (which has JSONB for "document" storage, PostGIS.net, Timescale.com, etc)?

edit 2: where can I find more technical, concrete examples than https://neo4j.com/use-cases?

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Re:Ask HN: What was your experience using a graph database? by chrisseaton on Monday December 31, 2018 @02:06PM (#18796281)
> What sort of problems are well-suited to graph databases?

If you have a graph, then a graph database, with built-in graph algorithms, will be able to run operations on your graph without pulling all the data out to a client. I'm not an expert in PostgreSQL but I don't think it has any graph algorithms?

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Re:Ask HN: What was your experience using a graph database? by vonholstein on Monday December 31, 2018 @08:43PM (#18798370)
My team opted for postgres over a graph db in one of our projects to model a network of devices. Primarily due to the pgRouting extension, which implements many graph algorithms in postgres.

https://pgrouting.org/

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Re:Ask HN: What was your experience using a graph database? by chadcmulligan on Monday December 31, 2018 @06:46PM (#18797871)
I've implemented graphs and trees in a relational DB quite a few times. For graphs you can just store an adjacency list. I think most of the large DB's now have tree traversal extensions to SQL (I know Oracle does). If you need to manipulate on the server then PL/Sql (or equivalent) can do the job.

The only time I could imagine that you'd need a specialist graph database would be if you had a very large number of nodes and some time / space intensive algorithm to run over them. Even in this case you could just store the data in a relational DB and use a low level interface (e.g. C) to write the specialist algorithm.

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Re:Ask HN: What was your experience using a graph database? by MichaelMoser123 on Monday December 31, 2018 @08:13PM (#18798260)
Yes, you need a nosql graph databases only for applications that require eventual consistency - and that's a hard thing to get right in any case; an application can do without that if does not have to scale to a very large user base.

In any case putting the graph nodes and links into sql tables is a much easier to do option.

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Re:Ask HN: What was your experience using a graph database? by allochthon on Monday December 31, 2018 @05:37PM (#18797493)
PG has recursive common table expressions, which allow you to traverse a tree or graph represented as an adjacency list in a single query. (No doubt there are other important things that graph DBs do.)
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Re:Ask HN: What was your experience using a graph database? by heurist on Monday December 31, 2018 @08:06PM (#18798238)
Are the built in graph algorithms useful these days? I tried neo4j a few years back and didnt find anything similar to eg networkx, which is the level of graph/network algorithms I use regularly. Neo4j made life much harder for me at the time, and I had to migrate that project back to postgres.
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Re:Ask HN: What was your experience using a graph database? by adamfeldman on Monday December 31, 2018 @02:11PM (#18796304)
Your question got me thinking, and led me to find this: https://github.com/bitnine-oss/agensgraph "AgensGraph, a transactional graph database based on PostgreSQL"
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Re:Ask HN: What was your experience using a graph database? by reaperducer on Monday December 31, 2018 @02:56PM (#18796581)
If you have a graph, then a graph database

How does one know if it's time to migrate to a graph database?

Right now I have a large (6.5GB) database that I have to sometimes work with, and the queries are getting more complex as more features are added to the project.

Right now the data is stored in MySQL, but to get anything interesting out of it requires multiple queries and then sifting through the data later. It all seems cumbersome.

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Re:Ask HN: What was your experience using a graph database? by chadcmulligan on Tuesday January 01, 2019 @01:44AM (#18799275)
It depends on the structure of the DB - 6.5GB is large if its attributes, if its documents then not so much. If its an index of documents then a different problem. Access patterns matter to. Like if its a 6.5 GB database that stores OLTP data, then yes thats large. If its a history of document modifications then probably small. If its historical data for a data cube sort of app, then its pretty small, I'd say tiny - I've worked on ones that get into the TB's.
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Re:Ask HN: What was your experience using a graph database? by reaperducer on Tuesday January 01, 2019 @11:31AM (#18800790)
It's all attributes; no documents being stored. About 2m records.
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Re:Ask HN: What was your experience using a graph database? by chadcmulligan on Tuesday January 01, 2019 @03:51PM (#18802275)
So thats a bit over 3k per record. Forgive my curiosity but whats the application domain? Thats a lot of info per record.
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Re:Ask HN: What was your experience using a graph database? by unixhero on Monday December 31, 2018 @08:15PM (#18798272)
Better port that sucker to Postgres sooner rather than later. You know, for future proofing.
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Re:Ask HN: What was your experience using a graph database? by dogweather on Monday December 31, 2018 @07:19PM (#18798057)
How about hierarchical data? E.g., a country's laws / statutes? Thousands of text files organized in a hierachy. I've resorted to relational denormalizing and hacks to get decent performance. So I'm wondering if a graph database would be a better fit.

E.g., I frequently need to query, "What is the list of ancestors from the object to the top of the tree?"

In a relational system, this needs to be stored in some kind of data structure, which is redundant. But theoretically in a graph database, it'd be a fast O(log n) query if I'm not mistaken.

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Re:Ask HN: What was your experience using a graph database? by jkern on Monday December 31, 2018 @02:54PM (#18796568)
My understanding is that graph databases are better suited to handling many-to-many relationships
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Re:Ask HN: What was your experience using a graph database? by chiefalchemist on Monday December 31, 2018 @03:25PM (#18796753)
I'd put it slightly different, and more simplified:

It's about the relationships (between the nodes).

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Re:Ask HN: What was your experience using a graph database? by tiuPapa on Monday December 31, 2018 @02:03PM (#18796264)
Good question, I should probably add this to my original question. Personally, I am trying to build a recommendation engine of sorts and I think Graph DB is suited for this but I am no expert.
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