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Netflix/hollow

Hollow is a java library and toolset for disseminating in-memory datasets from a single producer to many consumers for high performance read-only access.

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Repo info

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Adrian Baker

@adrian-skybaker

I was extremely dismayed to discover this week that the producer validation listeners (eg DuplicateDataDetectionValidator) run after content has been written out to the persisted blob store.

Although it did prevent the faulty version from being announced, the resulting cleanup has proved hard enough that we've given up and will just create a brand new blob store and get all clients to switch.

Although this post-write validation behaviour is actually documented, it's extremely surprising and greatly reduces the usefulness of the validators.

Drew Koszewnik

@dkoszewnik

@adrian-skybaker can you please help me understand why this resulted in a difficult cleanup? CB failures happen very often for us, and we find it useful to be able to retrieve the "bad" blobs from the blob store. Once the underlying issue is corrected, the next produced state will have a delta from the last announced state (artifacts for which are also still around in the blob store). We never actually do any sort of manual cleanup of the blob store after this event.

2 replies

Sahith Nallapareddy

@snallapa

hello I am wondering is there some sort of delay that occurs after applying a delta? i have a hollow dataset that use daily producer jobs. In the consumer, we use the unique key index to query the dataset. Everyday I can see the logs that the deltas are applied, however sometimes it seems that when the consumer queries the data for keys that should exist, it returns null. I setup a test consumer and queried the snapshot myself and found that the key does exist. After restarting our consumer we find that the consumer does find the data this time. Wondering if we waited longer would the consumer eventually be able to query the key? or could there be some weird bug in our implementation of some of the hollow classes

2 replies

Sahith Nallapareddy

@snallapa

similarly are there cases where a delta is applied but unique key index do not update? i am finding weird issues with longer running consumers. Keys do not seem to be found, but I have confirmed that deltas were applied and that the snapshot itself contains those keys

3 replies

graham_ren

@graham_ren:matrix.org

[m]

Hello, I am using Hollow:7.1.1
producer init:
val producer = HollowProducer.withPublisher(publisher).withAnnouncer(announcer)
.withNumStatesBetweenSnapshots(5)
.buildIncremental()
write data:
s3Producer.runIncrementalCycle { writer ->
writer.addOrModify(data)
}

I have encountered such error: Caused by: java.io.IOException: Attempting to apply a delta to a state from which it was not originated!

Can someone help tell me how to fix this?

Jeeukrishnan Kayshyap

@Jeeukrishnan

Hi.

I am getting hollow files to generated at runtime , after these files get generated,I can use consumer because it is using .withgeneratedAPIClass() function. How can I get rid of this function or how can I generate entire Hollow files in compile time itself?

Jeeukrishnan Kayshyap

@Jeeukrishnan

And why Netflix decided to generate custom apis after execution of producer code ? What can be their use case ? Is there any ways to generate these apis at compile time?

Jeeukrishnan Kayshyap

@Jeeukrishnan

Hi , any sort of help anyone can provide?

Alexandru-Gabriel Gherguț

@AlexandruGhergut

@Jeeukrishnan check out this plugin https://github.com/nebula-plugins/nebula-hollow-plugin. It adds a gradle task that you can call at build time to generate the API before compilation. If you don't want to use the plugin, you could probably write some custom Java code yourself that you can call at build time

mailsanchu

@mailsanchu

@Jeeukrishnan Did you google this before posting it here?

Jeeukrishnan Kayshyap

@Jeeukrishnan

@mailsanchu yes I did sir

@AlexandruGhergut Hi, thanks for your response,But could you please help me with maven. I tried googling and tried using dependency that I found , but it seems APIs are still not getting generated, please give some guidance!

mailsanchu

@mailsanchu

@Jeeukrishnan Need to improve your googling skills. here is an example with my skills https://github.com/IgorPerikov/hollow-maven-plugin-examples/blob/master/single-module-example/pom.xml

learnerjava830

@learnerjava830

What is the best open source tool/software for performance verfiying to identify performance bugs in Java?

learnerjava830

@learnerjava830

Text Over Image with Java Web Application

https://www.baeldung.com/java-add-text-to-image
https://www.geeksforgeeks.org/java-program-to-add-text-to-an-image-in-opencv/

I want to display an image in the web application where user can add text on the image.

Finally i need to save in DB, later user has to view the editable text and edit if required

How to achieve this in java web application - UI? back-end? DB (json or image or co-ordinates) ?

Does any opensource can be used in all the levels? Can someone suggest some comments/feedback

learnerjava830

@learnerjava830

URL url = new URL(...); --> FAILS here when i try to download a https image - "javax.imageio.IIOException ... "Can't get input stream from URL!""

Note:
URL works from browser
URL works in standalone program
URL fails when used in java web application

Question:

Is any special treatment required to access https image from web app?
How does it works in standalone program but not via web app though the certs are not installed in local machine?

What is the correct/right approach and what is the underlying differences?

Thanks

eric

@eric:matrix.h.etbus.ch

[m]

@learnerjava830: This is not an appropriate forum for questions like these, and I suspect you are some kind of linkspam bot. Please try this elsewhere.

mailsanchu

@mailsanchu

Why the explorer is showing values as null in text mode.If I select json values displaying correctly

mailsanchu

@mailsanchu

Anybody noticed this behaviour and is there a solution to this problem?

Drew Koszewnik

@dkoszewnik

@mailsanchu I have seen that before! But it seems relatively rare and we haven't had an opportunity to dig into it. If you happen to have a record in a dataset that reliably reproduces this, would you be able to hook up a debugger and find the bug? We would be glad to accept a PR if you happen to have a good opportunity to diagnose the issue.

mailsanchu

@mailsanchu

@dkoszewnik Here it is Netflix/hollow#573

Drew Koszewnik

@dkoszewnik

@mailsanchu that's awesome. Thanks very much I'm releasing v7.1.5 right now with your fix.

mailsanchu

@mailsanchu

I realized this may have fixed bug other bugs too new GenericHollowObject(hollowReadStateEngine, tye, ordinal).toString() was returning null string in some cases

@dkoszewnik Thank you

Ivan Zemlyanskiy

@QIvan

hello! I know it's not a big deal, but the official site with a quick start https://hollow.how/quick-start/ has a reference to an utterly out-of-date repo https://github.com/Netflix/hollow-reference-implementation
the gradle wrapper can work only with java-8 and the hallow version is 2.6.8

I could've fixed that, but there are already a lot of PRs in the project with version updates https://github.com/Netflix/hollow-reference-implementation/pulls

could someone take a look at the PRs?
for example this one looks promising Netflix/hollow-reference-implementation#16

Ivan Zemlyanskiy

@QIvan

I know the current version is 7.1.7 but it's a reasonable start isn't it?

thank you

Ivan Zemlyanskiy

@QIvan

@dkoszewnik @toolbear @kination (it says you are the 3 main contributors for the reference implementation project )

Ivan Zemlyanskiy

@QIvan

is it dead?

Sunjeet

@Sunjeet

Hi Ivan, I can look into this, likely next week because traveling. Thanks for the suggestion, I haven't worked with that repo yet, my initial thought is to bring it up to date to hollow 7 but maybe we could at least do the thing you suggested. Either way, more next week.

Ivan Zemlyanskiy

@QIvan

cool! Thank you @Sunjeet yesterday I spend some time with it and I upgraded the dependencies even more.
I'll make a PR in the near future, and will ask you to take into account my work as well

if someone knows @IgorPerikov please let him know that I made an update for the maven plugin IgorPerikov/hollow-maven-plugin#17
I added it to the reference implementation, but I guess we will need to release my upgrade in the plugin first

Ivan Zemlyanskiy

@QIvan

@Sunjeet as far as you're here, could you tell me what needs to be done for this PR? Netflix/hollow#552
just resolve the conflicts, right?

Ivan Zemlyanskiy

@QIvan

@Sunjeet, I upgraded everything even further please review this PR Netflix/hollow-reference-implementation#26

and I guess this PR should address all the open issues in the project =)

Jörgen Rydenius

@rydenius

Hi. I opened Netflix/hollow#578 about a transitive security vulnerability that hollow-ui-tools brings. I submitted Netflix/hollow#579 as an attempt to fix it. Would appreciate if someone had time to review it.

Sunjeet

@Sunjeet

@QIvan I left a minor comment in Netflix/hollow-reference-implementation#26

@rydenius thanks for Netflix/hollow#579 , give us some time to test backwards compatibility

Sunjeet

@Sunjeet

@QIvan With Netflix/hollow#552 I think we're almost there but there is some ambiguity in rollout. I don't fully understand if there a better approach to meet all 3 use cases- write a unit test that depends on hollow-tools, Guice apps that depend on hollow-tools that ship with jetty, and Springboot apps that depend on hollow-tools that ship with tomcat. Some more investigation required before merging that one, and probably wont be able to get to it soon

Ivan Zemlyanskiy

@QIvan

got it, thanks!
But keep in mind that that jetty-server version has a number vulnerabilities
https://mvnrepository.com/artifact/org.eclipse.jetty/jetty-server/9.4.3.v20170317

and because this hollow thing might be used for some privacy sensitive data, it might be a problem if someone has an access to the whole UI or just the data itself

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