Hi all,
The issue is solved.
I conducted a lot more testing and built checkers to verify at which size it's
going wrong.
When checking for specific edges, I could construct successful graphs up to
261k records.
When verifying all edges created, is breaks somewhere in the 200-250k records.
I didn't bother finding the specific error threshold, as runs take up to 7
minutes per slice.
I started looking at all underlying assumptions of my code along with my
supervisor.
We located the problem in the generate_ids() function.
I selected all distinct values to give them an ID and subsequently joining
those results back to the main DataFrame.
I replaced this by generating unique IDs for each value occurrence by hashing
them with 'withColumn' rather than joining them back.
This resolved my issues and ended up to be a significant performance boost as
well.
My fixed generate_ids() code
def generate_ids(df: DataFrame) -> DataFrame:
"""
Generates a unique ID for each distinct maintainer, prefix, origin and
organisation
Parameters
----------
df : DataFrame
DataFrame to generate IDs for
"""
df = df.withColumn(MAINTAINER_ID, psf.concat(psf.lit(PREFIX_M),
psf.sha2(df.mnt_by, 256)))
df = df.withColumn(PREFIX_ID, psf.concat(psf.lit(PREFIX_P),
psf.sha2(df.prefix, 256)))
df = df.withColumn(ORIGIN_ID, psf.concat(psf.lit(PREFIX_O),
psf.sha2(df.origin, 256)))
df = df.withColumn(ORGANISATION_ID, psf.concat(psf.lit(PREFIX_ORG),
psf.sha2(df.descr, 256)))
return df
Hope this email finds someone running into a similar issue in the future.
Kind regards,
Jelle
________________________________
From: Mich Talebzadeh <[email protected]>
Sent: Wednesday, May 1, 2024 11:56 AM
To: Stephen Coy <[email protected]>
Cc: Nijland, J.G.W. (Jelle, Student M-CS) <[email protected]>;
[email protected] <[email protected]>
Subject: Re: [spark-graphframes]: Generating incorrect edges
Hi Steve,
Thanks for your statement. I tend to use uuid myself to avoid collisions. This
built-in function generates random IDs that are highly likely to be unique
across systems. My concerns are on edge so to speak. If the Spark application
runs for a very long time or encounters restarts, the
monotonically_increasing_id() sequence might restart from the beginning. This
could again cause duplicate IDs if other Spark applications are running
concurrently or if data is processed across multiple runs of the same
application..
HTH
Mich Talebzadeh,
Technologist | Architect | Data Engineer | Generative AI | FinCrime
London
United Kingdom
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view my Linkedin
profile<https://www.linkedin.com/in/mich-talebzadeh-ph-d-5205b2/>
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Disclaimer: The information provided is correct to the best of my knowledge but
of course cannot be guaranteed . It is essential to note that, as with any
advice, quote "one test result is worth one-thousand expert opinions (Werner
<https://en.wikipedia.org/wiki/Wernher_von_Braun> Von
Braun<https://en.wikipedia.org/wiki/Wernher_von_Braun>)".
On Wed, 1 May 2024 at 01:22, Stephen Coy
<[email protected]<mailto:[email protected]>> wrote:
Hi Mich,
I was just reading random questions on the user list when I noticed that you
said:
On 25 Apr 2024, at 2:12 AM, Mich Talebzadeh
<[email protected]<mailto:[email protected]>> wrote:
1) You are using monotonically_increasing_id(), which is not
collision-resistant in distributed environments like Spark. Multiple hosts
can generate the same ID. I suggest switching to UUIDs (e.g., uuid.uuid4())
for guaranteed uniqueness.
It’s my understanding that the *Spark* `monotonically_increasing_id()` function
exists for the exact purpose of generating a collision-resistant unique id
across nodes on different hosts.
We use it extensively for this purpose and have never encountered an issue.
Are we wrong or are you thinking of a different (not Spark) function?
Cheers,
Steve C
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