45 lines
2.4 KiB
Text
45 lines
2.4 KiB
Text
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The Google 2019 Borg cluster traces analysis were conducted by using Apache
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Spark and its Python 3 API (pyspark). Spark was used to execute a series of
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queries to perform various sums and aggregations over the entire dataset
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provided by Google.
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In general, each query follows a general Map-Reduce template, where traces are
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first read, parsed, filtered by performing selections, projections and computing
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new derived fields. Then, the trace records are often grouped by one of their
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fields, clustering related data toghether before a reduce or fold operation is
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applied to each grouping.
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Most input data is in JSONL format and adheres to a schema Google profided in
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the form of a protobuffer specification located here:
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https://github.com/google/cluster-data/blob/master/clusterdata_trace_format_v3.proto
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On of the main quirks in the traces is that fields that have a "zero" value
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(i.e. a value like 0 or the empty string) are often omitted in the JSON object
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records. When reading the traces in Apache Spark is therefore necessary to check
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for this possibility and populate those zero fields when omitted.
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Most queries use only two or three fields in each trace records, while the
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original records often are made of a couple of dozen fields. In order to save
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memory during the query, a projection is often applied to the data by the means
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of a .map() operation over the entire trace set, performed using Spark's RDD
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API.
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Another operation that is often necessary to perform prior to the Map-Reduce core of
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each query is a record filtering process, which is often motivated by the
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presence of incomplete data (i.e. records which contain fields whose values is
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unknown). This filtering is performed using the .filter() operation of Spark's
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RDD API.
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The core of each query is often a groupBy followed by a map() operation on the
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aggregated data. The groupby groups the set of all records into several subsets
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of records each having something in common. Then, each of this small clusters is
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reduced with a .map() operation to a single record. The motivation behind this
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computation is often to analyze a time series of several different traces of
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programs. This is implemented by groupBy()-ing records by program id, and then
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map()-ing each program trace set by sorting by time the traces and computing the
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desired property in the form of a record.
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Sometimes intermediate results are saved in Spark's parquet format in order to
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compute and save intermediate results beforehand.
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