[GitHub] [incubator-pinot] kishoreg commented on a change in pull request #4435: Onboarding best practices doc

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kishoreg commented on a change in pull request #4435: Onboarding best practices doc
URL: https://github.com/apache/incubator-pinot/pull/4435#discussion_r304615454
 
 

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 File path: docs/onboarding_best_practices.rst
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+
+.. _onboarding-best-practices:
+
+Onboarding Best Practices
+==========================
+
+Here's a checklist of things to consider before you begin the process of modelling your data and onboarding to Pinot
+
+This has been split up into 2 sections: 
+
+1) Data Preparation 
+2) Querying Pinot
+
+
+
+Data Preparation
+^^^^^^^^^^^^^^^^^
+These are the best practices and considerations when preparing your data schema and data format
+
+Considerations common to offline and realtime
+**********************************************
+
+1. Pre-aggregations
+###################
+Pre aggregate the data as much as the application logic allows. This means **rolling up the metric values for the unique dimensions and time column combinations**. This is beneficial as we will reduce the size of the data being stored in Pinot, as well as avoid aggregations to be done in Pinot for every query, hence improving query performance. 
+
+- For offline, perform the aggregations in your data preparation hadoop/spark job. 
+- For realtime, a samza job can be used to aggregate data at intervals based on the freshness requirements of the usecase.
+
+2. Time column
+###################
+Think about what **granularity of time column** is needed for your application. This will usually be *HOURS, DAYS, (sometimes 15 MINUTES)*. It is not recommended to have the time column in MILLISECONDS or SECONDS granularity. If time granularity is in milliseconds, the cardinality of the time column becomes very high in realtime systems, causing the time column dictionary to get very big. Bucket your time column to the coarsest granularity possible (hoursSinceEpoch, daysSinceEpoch). A greater level of pre-aggregations can be achieved with coarser time granularity.
 
 Review comment:
   +1. We should just say use the pick the right granularity needed for your application and explain the trade-off. I would just remove ```It is not recommended to have the time column in MILLISECONDS or SECONDS granularity.```

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