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https://issues.apache.org/jira/browse/OAK-8523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17150231#comment-17150231
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Thomas Mueller commented on OAK-8523:
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Target: the node that is referenced. Source: the node where the target is
referenced.
I understand that someone might want to use paths instead of UUIDs. It can
still be done using an index.
Storing the *path* of the target node in the source node:
* Easy to read for humans.
* Simple lookup to the target from the source: Session.getNode(absPath).
* Disadvantage: need to update if the target is moved.
* Disadvantage: need to run a query to get the list of sources.
Storing the *UUID* of the target node in the source node:
* Disadvantage: Hard to read for humans.
* Simple to lookup the target from the source:
Session.getNodeByIdentifier(uuid).
* No need to update anything is the target is moved.
* Simple to get the list of sources: Node.getReferences()
* Disadvantage: best only add a UUID if the node is actually referenced, to
avoid an unnecessary entry in the UUID index.
Storing the *list of sources* in the target node:
* Potentially a huge number of entries in the target (for example: if a
"header" or "footer" referenced in millions of nodes). Needs to be updated
whenever a reference is added or removed, which can lead to an exponential time
algorithm and storage requirement.
* Potentially can result in out-of-memory during indexing or other operations.
> Best Practices - Property Value Length Limit
> --------------------------------------------
>
> Key: OAK-8523
> URL: https://issues.apache.org/jira/browse/OAK-8523
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: core, jcr
> Reporter: Thomas Mueller
> Priority: Major
>
> Right now, Oak supports very large properties (e.g. String). But 1 MB (or
> larger) properties are problematic in multiple areas like indexing. It is
> more important for software-as-a-service, where we need to guarantee SLOs,
> but it also helps other cases. So we should:
> * (1) Document best practises, e.g. "Property values should be smaller than
> 100 KB".
> * (2) Introduce "softLimit" and "hardLimit", where softLimit is e.g. 100 KB
> and hardLimit is configurable, and (initially) by default Integer.MAX_VALUE.
> Setting the hard limits to a lower value by default is problematic, because
> it can break existing applications. With default value infinity, customers
> can set lower limits e.g. in tests first, and once they are happy, in
> production as well.
> * (3) Log a warning if a property is larger than "softLimit". To avoid
> logging many warnings (if there are many such properties) we then set
> softLimit = softLimit * 1.1 (reset to 100 KB in the next repository start).
> Logging is needed to know what _exactly_ is broken (path, stack trace of the
> actual usage...)
> * (4) Add a metric (monitoring) for detected large properties. Just logging
> warnings might not be enough.
> * (5) Throttling: we could add flow control (pauses; Thread.sleep) after
> violations, to improve isolation (to prevent affecting other threads that
> don't violate the contract).
> * (6) We could expose the violation info in the session, so a framework could
> check that data after executing custom code, and add more info (e.g. log).
> * (7) If larger than the configurable hardLimit, fail the commit or reject
> setProperty (throw an exception).
> * (8) At some point, in a new Oak version, change the default value for
> hardLimit to some reasonable number, e.g. 1 MB.
> The "property length" is just one case. There are multiple candidates:
>
> * Number of properties for a node
> * Number of elements for multi-valued properties
> * Total size of a node (including inlined properties)
> * Number of direct child nodes for orderable child nodes
> * Number of direct child nodes for non-orderable child nodes
> * Size of transaction
> * Adding observations listeners that listen for all changes (global listeners)
> For those cases, new Jira issue should be made.
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