Sorry but I didn't get the question. It is possible that 1 record is present in multiple directories. That's why we do a reduceByKey after the union step.
On Wed, May 5, 2021 at 9:20 PM Mich Talebzadeh <mich.talebza...@gmail.com> wrote: > When you are doing union on these RDDs, (each RDD has one to one > correspondence with an HDFS directory), do you have a common key across all? > > > view my Linkedin profile > <https://www.linkedin.com/in/mich-talebzadeh-ph-d-5205b2/> > > > > *Disclaimer:* Use it at your own risk. Any and all responsibility for any > loss, damage or destruction of data or any other property which may arise > from relying on this email's technical content is explicitly disclaimed. > The author will in no case be liable for any monetary damages arising from > such loss, damage or destruction. > > > > > On Wed, 5 May 2021 at 16:23, Kapil Garg <kapi...@flipkart.com> wrote: > >> Hi Mich, >> I went through the thread and it doesn't relate to the problem statement >> I shared above. >> >> In my problem statement, there is a simple ETL job which doesn't use any >> external library (such as pandas) >> This is the flow >> >> *hdfsDirs := List<String>(); //contains N directories* >> >> *rddList := List<RDD>();* >> *for each directory in hdfsDirs:* >> * rdd = spark.read(directory)* >> * rdd.map() //augment the data with additional directory related data* >> * rddList.add(rdd)* >> >> *finalRdd = spark.union(rddList) // number of tasks = N*K // Files are >> distributed unevenly on executors here* >> >> *finalRdd.partionBy(hashpartitioner); // here tasks take uneven time* >> >> Is it possible to make the union step read the directory evenly on each >> executor, that way, each executor will have roughly the same amount of data >> >> >> >> On Wed, May 5, 2021 at 8:35 PM Mich Talebzadeh <mich.talebza...@gmail.com> >> wrote: >> >>> Hi, >>> >>> Have a look at this thread called >>> >>> Tasks are skewed to one executor >>> >>> and see if it helps and we can take it from there. >>> >>> HTH >>> >>> >>> >>> view my Linkedin profile >>> <https://www.linkedin.com/in/mich-talebzadeh-ph-d-5205b2/> >>> >>> >>> >>> *Disclaimer:* Use it at your own risk. Any and all responsibility for >>> any loss, damage or destruction of data or any other property which may >>> arise from relying on this email's technical content is explicitly >>> disclaimed. The author will in no case be liable for any monetary damages >>> arising from such loss, damage or destruction. >>> >>> >>> >>> >>> On Wed, 5 May 2021 at 15:46, Kapil Garg <kapi...@flipkart.com.invalid> >>> wrote: >>> >>>> Hi, >>>> I am facing issues while reading multiple HDFS directories. Please read >>>> the problem statement and current approach below >>>> >>>> *Problem Statement* >>>> There are N HDFS directories each having K files. We want to read data >>>> from all directories such that when we read data from directory D, we map >>>> all the data and augment it with additional information specific to that >>>> directory. >>>> >>>> *Current Approach* >>>> In current approach, we are iterating over the directories, reading it >>>> in RDD, mapping the RDD and the putting the RDD into a list. >>>> After all N directories have been read, we have a list of N RDDs >>>> We call spark Union on the list to merge them together. >>>> >>>> This approach is causing data skewness because there is 1 directory of >>>> size 12 GBs whereas other RDDs are less than 1 GB. So when the large RDD's >>>> turn comes, spark submits its task on available executors causing the RDD >>>> to present on few executors instead of spreading on all. >>>> >>>> Is there a way to avoid this data skewness ? I couldn't find any RDD >>>> API, spark config which could enforce the data reading tasks evenly on all >>>> executors. >>>> >>>> -- >>>> Regards >>>> Kapil Garg >>>> >>>> >>>> *-----------------------------------------------------------------------------------------* >>>> >>>> *This email and any files transmitted with it are confidential and >>>> intended solely for the use of the individual or entity to whom they are >>>> addressed. If you have received this email in error, please notify the >>>> system manager. This message contains confidential information and is >>>> intended only for the individual named. If you are not the named addressee, >>>> you should not disseminate, distribute or copy this email. Please notify >>>> the sender immediately by email if you have received this email by mistake >>>> and delete this email from your system. If you are not the intended >>>> recipient, you are notified that disclosing, copying, distributing or >>>> taking any action in reliance on the contents of this information is >>>> strictly prohibited.* >>>> >>>> >>>> >>>> *Any views or opinions presented in this email are solely those of the >>>> author and do not necessarily represent those of the organization. Any >>>> information on shares, debentures or similar instruments, recommended >>>> product pricing, valuations and the like are for information purposes only. >>>> It is not meant to be an instruction or recommendation, as the case may be, >>>> to buy or to sell securities, products, services nor an offer to buy or >>>> sell securities, products or services unless specifically stated to be so >>>> on behalf of the Flipkart group. Employees of the Flipkart group of >>>> companies are expressly required not to make defamatory statements and not >>>> to infringe or authorise any infringement of copyright or any other legal >>>> right by email communications. Any such communication is contrary to >>>> organizational policy and outside the scope of the employment of the >>>> individual concerned. The organization will not accept any liability in >>>> respect of such communication, and the employee responsible will be >>>> personally liable for any damages or other liability arising.* >>>> >>>> >>>> >>>> *Our organization accepts no liability for the content of this email, >>>> or for the consequences of any actions taken on the basis of the >>>> information *provided,* unless that information is subsequently >>>> confirmed in writing. If you are not the intended recipient, you are >>>> notified that disclosing, copying, distributing or taking any action in >>>> reliance on the contents of this information is strictly prohibited.* >>>> >>>> >>>> *-----------------------------------------------------------------------------------------* >>>> >>>> >> >> -- >> Regards >> Kapil Garg >> >> >> *-----------------------------------------------------------------------------------------* >> >> *This email and any files transmitted with it are confidential and >> intended solely for the use of the individual or entity to whom they are >> addressed. If you have received this email in error, please notify the >> system manager. This message contains confidential information and is >> intended only for the individual named. If you are not the named addressee, >> you should not disseminate, distribute or copy this email. Please notify >> the sender immediately by email if you have received this email by mistake >> and delete this email from your system. If you are not the intended >> recipient, you are notified that disclosing, copying, distributing or >> taking any action in reliance on the contents of this information is >> strictly prohibited.* >> >> >> >> *Any views or opinions presented in this email are solely those of the >> author and do not necessarily represent those of the organization. Any >> information on shares, debentures or similar instruments, recommended >> product pricing, valuations and the like are for information purposes only. >> It is not meant to be an instruction or recommendation, as the case may be, >> to buy or to sell securities, products, services nor an offer to buy or >> sell securities, products or services unless specifically stated to be so >> on behalf of the Flipkart group. Employees of the Flipkart group of >> companies are expressly required not to make defamatory statements and not >> to infringe or authorise any infringement of copyright or any other legal >> right by email communications. Any such communication is contrary to >> organizational policy and outside the scope of the employment of the >> individual concerned. The organization will not accept any liability in >> respect of such communication, and the employee responsible will be >> personally liable for any damages or other liability arising.* >> >> >> >> *Our organization accepts no liability for the content of this email, or >> for the consequences of any actions taken on the basis of the information * >> provided,* unless that information is subsequently confirmed in writing. >> If you are not the intended recipient, you are notified that disclosing, >> copying, distributing or taking any action in reliance on the contents of >> this information is strictly prohibited.* >> >> >> *-----------------------------------------------------------------------------------------* >> >> -- Regards Kapil Garg -- *-----------------------------------------------------------------------------------------* *This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. 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It is not meant to be an instruction or recommendation, as the case may be, to buy or to sell securities, products, services nor an offer to buy or sell securities, products or services unless specifically stated to be so on behalf of the Flipkart group. Employees of the Flipkart group of companies are expressly required not to make defamatory statements and not to infringe or authorise any infringement of copyright or any other legal right by email communications. Any such communication is contrary to organizational policy and outside the scope of the employment of the individual concerned. 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