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---
documentclass: usiinfbachelorproject
title: Understanding and Comparing Unsuccessful Executions in Large Datacenters
author: Claudio Maggioni
pandoc-options:
- --filter=pandoc-include
- --latex-engine-opt=--shell-escape
- --latex-engine-opt=--enable-write18
header-includes:
- |
```{=latex}
\usepackage{subcaption}
\usepackage{booktabs}
\usepackage{graphicx}
\captionsetup{labelfont={bf}}
%\subtitle{The (optional) subtitle}
\versiondate{\today}
\begin{committee}
\advisor[Universit\`a della Svizzera Italiana,
Switzerland]{Prof.}{Walter}{Binder}
\assistant[Universit\`a della Svizzera Italiana,
Switzerland]{Dr.}{Andrea}{Ros\'a}
\end{committee}
\abstract{The project aims at comparing two different traces coming from large
datacenters, focusing in particular on unsuccessful executions of jobs and
tasks submitted by users. The objective of this project is to compare the
resource waste caused by unsuccessful executions, their impact on application
performance, and their root causes. We will show the strong negative impact on
CPU and RAM usage and on task slowdown. We will analyze patterns of
unsuccessful jobs and tasks, particularly focusing on their interdependency.
Moreover, we will uncover their root causes by inspecting key workload and
system attributes such asmachine locality and concurrency level.}
```
---
\tableofcontents
\newpage
# Introduction (including Motivation)
# State of the Art
## Introduction
**TBD**
## Rosà et al. 2015 DSN paper
In 2015, Dr. Andrea Rosà, Lydia Y. Chen, Prof. Walter Binder published a
research paper titled "Understanding the Dark Side of Big Data Clusters:
An Analysis beyond Failures" performing several analysis on Google's 2011
Borg cluster traces. The salient conclusion of that research is that lots of
computation performed by Google would eventually fail, leading to large amounts
of computational power being wasted.
Our aim with this thesis is to repeat the analysis performed in 2015 on the new
2019 dataset to find similarities and differences with the previous analysis,
and ulimately find if computational power is indeed wasted in this new workload
as well.
## Google Borg
Borg is Google's own cluster management software. Among the various cluster
management services it provides, the main ones are: job queuing, scheduling,
allocation, and deallocation due to higher priority computations.
The data this thesis is based on is from 8 Borg "cells" (i.e. clusters) spanning
8 different datacenters, all focused on "compute" (i.e. computational oriented)
workloads. The data collection timespan matches the entire month of May 2019.
In Google's lingo a "job" is a large unit of computational workload made up of
several "tasks", i.e. a number of executions of single executables running on a
single machine. A job may run tasks sequentially or in parallel, and the
condition for a job's succesful termination is nontrivial.
Both tasks and jobs lifecyles are represented by several events, which are
encoded and stored in the trace as rows of various tables. Among the information
events provide, the field "type" provides information on the execution status of
the job or task. This field can have the following values:
- **QUEUE**: The job or task was marked not eligible for scheduling by Borg's
scheduler, and thus Borg will move the job/task in a long wait queue;
- **SUBMIT**: The job or task was submitted to Borg for execution;
- **ENABLE**: The job or task became eligible for scheduling;
- **SCHEDULE**: The job or task's execution started;
- **EVICT**: The job or task was terminated in order to free computational
resources for an higher priority job;
- **FAIL**: The job or task terminated its execution unsuccesfully due to a
failure;
- **FINISH**: The job or task terminated succesfully;
- **KILL**: The job or task terminated its execution because of a manual request
to stop it;
- **LOST**: It is assumed a job or task is has been terminated, but due to
missing data there is insufficent information to identify when or how;
- **UPDATE_PENDING**: The metadata (scheduling class, resource requirements,
...) of the job/task was updated while the job was waiting to be scheduled;
- **UPDATE_RUNNING**: The metadata (scheduling class, resource requirements,
...) of the job/task was updated while the job was in execution;
Figure \ref{fig:eventTypes} shows the expected transitions between event types.
![Typical transitions between task/job event types according to Google
\label{fig:eventTypes}](./figures/event_types.png)
## Traces contents
The traces provided by Google contain mainly a collection of job and task events
spanning a month of execution of the 8 different clusters. In addition to this
data, some additional data on the machines' configuration in terms of resources
(i.e. amount of CPU and RAM) and additional machine-related metadata.
Due to Google's policy, most identification related data (like job/task IDs,
raw resource amounts and other text values) were obfuscated prior to the release
of the traces. One obfuscation that is noteworthy in the scope of this thesis is
related to CPU and RAM amounts, which are expressed respetively in NCUs
(_Normalized Compute Units_) and NMUs (_Normalized Memory Units_).
NCUs and NMUs are defined based on the raw machine resource distributions of the
machines within the 8 clusters. A machine having 1 NCU CPU power and 1 NMU
memory size has the maximum amount of raw CPU power and raw RAM size found in
the clusters. While RAM size is measured in bytes for normalization purposes,
CPU power was measured in GCU (_Google Compute Units_), a proprietary CPU power
measurement unit used by Google that combines several parameters like number of
processors and cores, clock frequency, and architecture (i.e. ISA).
## Overview of traces' format
The traces have a collective size of approximately 8TiB and are stored in a
Gzip-compressed JSONL (JSON lines) format, which means that each table is
represented by a single logical "file" (stored in several file segments) where
each carriage return separated line represents a single record for that table.
There are namely 5 different table "files":
- `machine_configs`, which is a table containing each physical machine's
configuration and its evolution over time;
- `instance_events`, which is a table of task events;
- `collection_events`, which is a table of job events;
- `machine_attributes`, which is a table containing (obfuscated) metadata about
each physical machine and its evolution over time;
- `instance_usage`, which contains resource (CPU/RAM) measures of jobs and tasks
running on the single machines.
The scope of this thesis focuses on the tables `machine_configs`,
`instance_events` and `collection_events`.
## Remark on traces size
While the 2011 Google Borg traces were relatively small, with a total size in
the order of the tens of gigabytes, the 2019 traces are quite challenging to
analyze due to their sheer size. As stated before, the traces have a total size
of 8 TiB when stored in the format provided by Google. Even when broken down to
table "files", unitary sizes still reach the single tebibyte mark (namely for
`machine_configs`, the largest table in the trace).
Due to this constraints, a careful data engineering based approach was used when
reproducing the 2015 DSN paper analysis. Bleeding edge data science technologies
like Apache Spark were used to achieve efficient and parallelized computations.
This approach is discussed with further detail in the following section.
# Project requirements and analysis
**TBD** (describe our objective with this analysis in detail)
# Analysis methodology
**TBD**
## Introduction on Apache Spark
Apache Spark is a unified analytics engine for large-scale data processing. In
layman's terms, Spark is really useful to parallelize computations in a fast and
streamlined way.
In the scope of this thesis, Spark was used essentially as a Map-Reduce
framework for computing aggregated results on the various tables. Due to the
sharded nature of table "files", Spark is able to spawn a thread per file and
run computations using all processors on the server machines used to run the
analysis.
Spark is also quite powerful since it provides automated thread pooling
services, and it is able to efficiently store and cache intermediate computation
on secondary storage without any additional effort required from the data
engineer. This feature was especially useful due to the sheer size of the
analyzed data, since the computations required to store up to 1TiB of
intermediate data on disk.
The chosen programming language for writing analysis scripts was Python. Spark
has very powerful native Python bindings in the form of the _PySpark_ API, which
were used to implement the various queries.
## Query architecture
In general, each query follows a general Map-Reduce template, where traces are
first read, parsed, filtered by performing selections, projections and computing
new derived fields. Then, the trace records are often grouped by one of their
fields, clustering related data toghether before a reduce or fold operation is
applied to each grouping.
Most input data is in JSONL format and adheres to a schema Google profided in
the form of a protobuffer specification[^1].
[^1]: [Google 2019 Borg traces Protobuffer specification on Github](
https://github.com/google/cluster-data/blob/master/clusterdata_trace_format_v3.proto)
On of the main quirks in the traces is that fields that have a "zero" value
(i.e. a value like 0 or the empty string) are often omitted in the JSON object
records. When reading the traces in Apache Spark is therefore necessary to check
for this possibility and populate those zero fields when omitted.
Most queries use only two or three fields in each trace records, while the
original records often are made of a couple of dozen fields. In order to save
memory during the query, a projection is often applied to the data by the means
of a .map() operation over the entire trace set, performed using Spark's RDD
API.
Another operation that is often necessary to perform prior to the Map-Reduce
core of each query is a record filtering process, which is often motivated by
the presence of incomplete data (i.e. records which contain fields whose values
is unknown). This filtering is performed using the .filter() operation of Spark's
RDD API.
The core of each query is often a groupBy followed by a map() operation on the
aggregated data. The groupby groups the set of all records into several subsets
of records each having something in common. Then, each of this small clusters is
reduced with a .map() operation to a single record. The motivation behind this
computation is often to analyze a time series of several different traces of
programs. This is implemented by groupBy()-ing records by program id, and then
map()-ing each program trace set by sorting by time the traces and computing the
desired property in the form of a record.
Sometimes intermediate results are saved in Spark's parquet format in order to
compute and save intermediate results beforehand.
## General Query script design
**TBD**
## Ad-Hoc presentation of some analysis scripts
**TBD** (with diagrams)
# Analysis and observations
## Overview of machine configurations in each cluster
\input{figures/machine_configs}
Refer to figure \ref{fig:machineconfigs}.
**Observations**:
- machine configurations are definitely more varied than the ones in the 2011
traces
- some clusters have more machine variability
## Analysis of execution time per each execution phase
\input{figures/machine_time_waste}
Refer to figures \ref{fig:machinetimewaste-abs} and
\ref{fig:machinetimewaste-rel}.
**Observations**:
- Across all cluster almost 50% of time is spent in "unknown" transitions, i.e.
there are some time slices that are related to a state transition that Google
says are not "typical" transitions. This is mostly due to the trace log being
intermittent when recording all state transitions.
- 80% of the time spent in KILL and LOST is unknown. This is predictable, since
both states indicate that the job execution is not stable (in particular LOST
is used when the state logging itself is unstable)
- From the absolute graph we see that the time "wasted" on non-finish terminated
jobs is very significant
- Execution is the most significant task phase, followed by queuing time and
scheduling time ("ready" state)
- In the absolute graph we see that a significant amount of time is spent to
re-schedule evicted jobs ("evicted" state)
- Cluster A has unusually high queuing times
## Task slowdown
\input{figures/task_slowdown}
Refer to figure \ref{fig:taskslowdown}
**Observations**:
- Priority values are different from 0-11 values in the 2011 traces. A
conversion table is provided by Google;
- For some priorities (e.g. 101 for cluster D) the relative number of finishing
task is very low and the mean slowdown is very high (315). This behaviour
differs from the relatively homogeneous values from the 2011 traces.
- Some slowdown values cannot be computed since either some tasks have a 0ns
execution time or for some priorities no tasks in the traces terminate
successfully. More raw data on those exception is in Jupyter.
- The % of finishing jobs is relatively low comparing with the 2011 traces.
## Reserved and actual resource usage of tasks
\input{figures/spatial_resource_waste}
Refer to figures \ref{fig:spatialresourcewaste-actual} and
\ref{fig:spatialresourcewaste-requested}.
**Observations**:
- Most (mesasured and requested) resources are used by killed job, even more
than in the 2011 traces.
- Behaviour is rather homogeneous across datacenters, with the exception of
cluster G where a lot of LOST-terminated tasks acquired 70% of both CPU and
RAM
## Correlation between task events' metadata and task termination
\input{figures/figure_7}
Refer to figures \ref{fig:figureVII-a}, \ref{fig:figureVII-b}, and
\ref{fig:figureVII-c}.
**Observations**:
- No smooth curves in this figure either, unlike 2011 traces
- The behaviour of curves for 7a (priority) is almost the opposite of 2011, i.e.
in-between priorities have higher kill rates while priorities at the extremum
have lower kill rates. This could also be due bt the inherent distribution of
job terminations;
- Event execution time curves are quite different than 2011, here it seems there
is a good correlation between short task execution times and finish event
rates, instead of the U shape curve in 2015 DSN
- In figure \ref{fig:figureVII-b} cluster behaviour seems quite uniform
- Machine concurrency seems to play little role in the event termination
distribution, as for all concurrency factors the kill rate is at 90%.
## Correlation between task events' resource metadata and task termination
## Correlation between job events' metadata and job termination
\input{figures/figure_9}
Refer to figures \ref{fig:figureIX-a}, \ref{fig:figureIX-b}, and
\ref{fig:figureIX-c}.
**Observations**:
- Behaviour between cluster varies a lot
- There are no "smooth" gradients in the various curves unlike in the 2011
traces
- Killed jobs have higher event rates in general, and overall dominate all event
rates measures
- There still seems to be a correlation between short execution job times and
successfull final termination, and likewise for kills and higher job
terminations
- Across all clusters, a machine locality factor of 1 seems to lead to the
highest success event rate
## Mean number of tasks and event distribution per task type
\input{figures/table_iii}
Refer to figure \ref{fig:tableIII}.
**Observations**:
- The mean number of events per task is an order of magnitude higher than in the
2011 traces
- Generally speaking, the event type with higher mean is the termination event
for the task
- The # evts mean is higher than the sum of all other event type means, since it
appears there are a lot more non-termination events in the 2019 traces.
## Mean number of tasks and event distribution per job type
\input{figures/table_iv}
Refer to figure \ref{fig:tableIV}.
**Observations**:
- Again the mean number of tasks is significantly higher than the 2011 traces,
indicating a higher complexity of workloads
- Cluster A has no evicted jobs
- The number of events is however lower than the event means in the 2011 traces
## Probability of task successful termination given its unsuccesful events
\input{figures/figure_5}
Refer to figure \ref{fig:figureV}.
**Observations**:
- Behaviour is very different from cluster to cluster
- There is no easy conclusion, unlike in 2011, on the correlation between
succesful probability and # of events of a specific type.
- Clusters B, C and D in particular have very unsmooth lines that vary a lot for
small # evts differences. This may be due to an uneven distribution of # evts
in the traces.
## Potential causes of unsuccesful executions
**TBD**
# Implementation issues -- Analysis limitations
## Discussion on unknown fields
**TBD**
## Limitation on computation resources required for the analysis
**TBD**
## Other limitations ...
**TBD**
# Conclusions and future work or possible developments
**TBD**
<!-- vim: set ts=2 sw=2 et tw=80: -->

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@ -2,6 +2,11 @@
\title{Understanding and Comparing Unsuccessful Executions in Large Datacenters}
\author{Claudio Maggioni}
\usepackage[parfill]{parskip}
\setlength{\parskip}{7pt}
\setlength{\parindent}{0pt}
\usepackage{xcolor}
\usepackage{amsmath}
\usepackage{subcaption}
\usepackage{booktabs}
@ -12,6 +17,7 @@
\versiondate{\today}
\begin{committee}
\advisor[Universit\`a della Svizzera Italiana,
Switzerland]{Prof.}{Walter}{Binder}
@ -30,7 +36,7 @@ Moreover, we will uncover their root causes by inspecting key workload and
system attributes such asmachine locality and concurrency level.}
\begin{document}
\maketitle
\tableofcontents
\newpage
@ -89,7 +95,6 @@ the execution status of the job or task. This field can have the
following values:
\begin{itemize}
\tightlist
\item
\textbf{QUEUE}: The job or task was marked not eligible for scheduling
by Borg's scheduler, and thus Borg will move the job/task in a long
@ -125,12 +130,13 @@ following values:
execution;
\end{itemize}
Figure \ref{fig:eventTypes} shows the expected transitions between event
Figure~\ref{fig:eventTypes} shows the expected transitions between event
types.
\begin{figure}
\centering
\includegraphics{./figures/event_types.png}
\resizebox{\textwidth}{!}{%
\includegraphics{./figures/event_types.png}}
\caption{Typical transitions between task/job event types according to
Google\label{fig:eventTypes}}
\end{figure}
@ -173,7 +179,6 @@ single record for that table.
There are namely 5 different table ``files'':
\begin{itemize}
\tightlist
\item
\texttt{machine\_configs}, which is a table containing each physical
machine's configuration and its evolution over time;
@ -249,46 +254,66 @@ Spark has very powerful native Python bindings in the form of the
\hypertarget{query-architecture}{%
\subsection{Query architecture}\label{query-architecture}}
In general, each query follows a general Map-Reduce template, where
traces are first read, parsed, filtered by performing selections,
projections and computing new derived fields. Then, the trace records
are often grouped by one of their fields, clustering related data
toghether before a reduce or fold operation is applied to each grouping.
\subsubsection{Overview}
Most input data is in JSONL format and adheres to a schema Google
profided in the form of a protobuffer specification\footnote{\href{https://github.com/google/cluster-data/blob/master/clusterdata_trace_format_v3.proto}{Google
2019 Borg traces Protobuffer specification on Github}}.
In general, each query written to execute the analysis
follows a general Map-Reduce template.
On of the main quirks in the traces is that fields that have a ``zero''
value (i.e.~a value like 0 or the empty string) are often omitted in the
JSON object records. When reading the traces in Apache Spark is
therefore necessary to check for this possibility and populate those
zero fields when omitted.
Traces are first read, then parsed, and then filtered by performing selections,
projections and computing new derived fields. After this preparation phase, the
trace records are often passed through a \texttt{groupby()} operation, which by
choosing one or many record fields sorts all the records into several ``bins''
containing records with matching values for the selected fields. Then, a map
operation is applied to each bin in order to derive some aggregated property
value for each grouping. Finally, a reduce operation is applied to either
further aggregate those computed properties or to generate an aggregated data
structure for storage purposes.
Most queries use only two or three fields in each trace records, while
the original records often are made of a couple of dozen fields. In
order to save memory during the query, a projection is often applied to
the data by the means of a .map() operation over the entire trace set,
performed using Spark's RDD API.
\subsubsection{Parsing table files}
Another operation that is often necessary to perform prior to the
Map-Reduce core of each query is a record filtering process, which is
often motivated by the presence of incomplete data (i.e.~records which
contain fields whose values is unknown). This filtering is performed
using the .filter() operation of Spark's RDD API.
As stated before, table ``files'' are composed of several Gzip-compressed
shards of JSONL record data. The specification for the types and constraints
of each record is outlined by Google in the form of a protobuffer specification
file found in the trace release
package.\footnote{\href{https://github.com/google/cluster-data/blob/master/clusterdata_trace_format_v3.proto}{Google
2019 Borg traces Protobuffer specification on Github}}. This file was used as
the oracle specification and was a critical reference for writing the query
code that checks, parses and carefully sanitizes the various JSONL records
prior to actual computations.
The core of each query is often a groupBy followed by a map() operation
on the aggregated data. The groupby groups the set of all records into
several subsets of records each having something in common. Then, each
of this small clusters is reduced with a .map() operation to a single
record. The motivation behind this computation is often to analyze a
time series of several different traces of programs. This is implemented
by groupBy()-ing records by program id, and then map()-ing each program
trace set by sorting by time the traces and computing the desired
property in the form of a record.
The JSONL encoding of traces records is often performed with non-trivial rules
that required careful attention. One of these involved fields that have a
logically-wise ``zero'' value (i.e.~values like ``0'' or the empty string). For
these values the key-value pair in the JSON object is outright omitted. When
reading the traces in Apache Spark is therefore necessary to check for this
possibility and insert back the omitted record attributes.
Sometimes intermediate results are saved in Spark's parquet format in
order to compute and save intermediate results beforehand.
\subsubsection{The queries}
Most queries use only two or three fields in each trace records, while the
original table records often are made of a couple of dozen fields. In order to save
memory during the query, a projection is often applied to the data by the means
of a \texttt{.map()} operation over the entire trace set, performed using
Spark's RDD API.
Another operation that is often necessary to perform prior to the Map-Reduce
core of each query is a record filtering process, which is often motivated by
the presence of incomplete data (i.e.~records which contain fields whose values
is unknown). This filtering is performed using the \texttt{.filter()} operation
of Spark's RDD API.
The core of each query is often a \texttt{groupby()} followed by a \texttt{map()}
operation on the aggregated data. The \texttt{groupby()} groups the set of all records
into several subsets of records each having something in common. Then, each of
this small clusters is reduced with a \texttt{map()} operation to a single
record. The motivation behind this computation is often to analyze a time
series of several different traces of programs. This is implemented by
\texttt{groupby()}-ing records by program id, and then \texttt{map()}-ing each program
trace set by sorting by time the traces and computing the desired property in
the form of a record.
Sometimes intermediate results are saved in Spark's parquet format in order to
compute and save intermediate results beforehand.
\hypertarget{general-query-script-design}{%
\subsection{General Query script
@ -316,7 +341,6 @@ Refer to figure \ref{fig:machineconfigs}.
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
machine configurations are definitely more varied than the ones in the
2011 traces
@ -336,7 +360,6 @@ Refer to figures \ref{fig:machinetimewaste-abs} and
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
Across all cluster almost 50\% of time is spent in ``unknown''
transitions, i.e. there are some time slices that are related to a
@ -371,7 +394,6 @@ Refer to figure \ref{fig:taskslowdown}
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
Priority values are different from 0-11 values in the 2011 traces. A
conversion table is provided by Google;
@ -402,7 +424,6 @@ Refer to figures \ref{fig:spatialresourcewaste-actual} and
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
Most (mesasured and requested) resources are used by killed job, even
more than in the 2011 traces.
@ -424,7 +445,6 @@ Refer to figures \ref{fig:figureVII-a}, \ref{fig:figureVII-b}, and
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
No smooth curves in this figure either, unlike 2011 traces
\item
@ -459,7 +479,6 @@ Refer to figures \ref{fig:figureIX-a}, \ref{fig:figureIX-b}, and
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
Behaviour between cluster varies a lot
\item
@ -488,7 +507,6 @@ Refer to figure \ref{fig:tableIII}.
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
The mean number of events per task is an order of magnitude higher
than in the 2011 traces
@ -512,7 +530,6 @@ Refer to figure \ref{fig:tableIV}.
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
Again the mean number of tasks is significantly higher than the 2011
traces, indicating a higher complexity of workloads
@ -535,7 +552,6 @@ Refer to figure \ref{fig:figureV}.
\textbf{Observations}:
\begin{itemize}
\tightlist
\item
Behaviour is very different from cluster to cluster
\item

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default:
mkdir -p build
pdflatex -output-directory=build Claudio_Maggioni_report
pdflatex -output-directory=build Claudio_Maggioni_report
pdflatex -output-directory=build Claudio_Maggioni_report
mv build/Claudio_Maggioni_report.pdf ./
quick:
mkdir -p build
pdflatex -output-directory=build Claudio_Maggioni_report
mv build/Claudio_Maggioni_report.pdf ./
clean:
rm -r build