Introduction to Riak

Introduction to Riak
Christopher Meiklejohn
BOBkonf 2015
@cmeik

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History

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Published SOSP 2007; key-value storage system
Amazon Dynamo

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Focused on high-availability and low-latency
Amazon Dynamo

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Collection of distributed systems techniques
Amazon Dynamo

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LinkedIn Voldemort, Facebook Cassandra
Amazon Dynamo

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Released 2009; Apache2 licensed Dynamo clone
Basho Riak

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Installing and Using Riak

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$ curl -O http://s3.amazonaws.com/downloads.basho.com/erlang/
otp_src_R16B02-basho5.tar.gz
$ tar -xvf otp_src_R16B02-basho5.tar.gz
$ cd otp_src_R16B02-basho5
$ ./configure && make && sudo make install
Installing Erlang

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$ git clone https://github.com/basho/riak.git
$ cd riak
$ make all
Building Riak

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$ make devrel DEVNODES=5
$ cd dev; ls
Building a devrel

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$ for node in dev*; do $node/bin/riak start; done
Starting a devrel

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$ for node in dev*; do $node/bin/riak ping; done
Pinging all nodes in a devrel

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$ dev2/bin/riak-admin cluster join [email protected]
Stage a join

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$ dev1/bin/riak-admin cluster plan
View a staged plan

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=============================== Staged Changes ================================
Action Nodes(s)
-------------------------------------------------------------------------------
join '[email protected]'
-------------------------------------------------------------------------------
NOTE: Applying these changes will result in 1 cluster transition
###############################################################################
After cluster transition 1/1
###############################################################################
================================= Membership ==================================
Status Ring Pending Node
-------------------------------------------------------------------------------
valid 100.0% 20.3% '[email protected]'
-------------------------------------------------------------------------------
Valid:5 / Leaving:0 / Exiting:0 / Joining:0 / Down:0
Transfers resulting from cluster changes: 51
12 transfers from '[email protected]' to '[email protected]'
View a staged plan

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$ dev2/bin/riak-admin cluster commit
Commit the plan

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$ dev1/bin/riak-admin member-status
View members of cluster

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================================= Membership ==================================
Status Ring Pending Node
-------------------------------------------------------------------------------
valid 20.3% -- '[email protected]'
-------------------------------------------------------------------------------
Valid:5 / Leaving:0 / Exiting:0 / Joining:0 / Down:0
View members of cluster

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$ curl -XPUT http://localhost:10018/buckets/welcome/keys/german -H
'Content-Type: text/plain' -d 'herzlich willkommen'
Storing data via HTTP

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$ curl http://localhost:10018/buckets/welcome/keys/german
Retrieving data via HTTP

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$ curl -XPUT http://localhost:10018/buckets/images/keys/
.jpg \
-H 'Content-Type: image/jpeg' \
--data-binary @.jpg
Storing an image via HTTP

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$ curl -O http://localhost:10018/buckets/images/keys/.jpg
Retrieving an image via HTTP

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Riak Architecture

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Consistent Hashing
hash(bucket/key)

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hash ring

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tokenize it

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node 0
node 1
node 2
hash(key)

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node 0
node 1
node 2
Replicas are stored to the N - 1
contiguous partitions

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node 0
node 1
node 2
hash(companies/cisco)
Replicas are stored to the N - 1
contiguous partitions

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node 0
node 1
node 2

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Scaling out
node 0
node 1
node 2
node 3 +

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Quorum
requests
N R W PR/PW DW

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Vector Clocks
establish temporality

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Anatomy of a Request
get(users/clay-davis)

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client
Riak

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Get Handler (FSM)
client
Riak

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Get Handler (FSM)
client
Riak
hash(users/clay-davis)
== 10, 11, 12

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Get Handler (FSM)
client
Riak
hash(users/clay-davis)
== 10, 11, 12
Coordinating node
Cluster
6 7 8 9 10 11 12 13 14 15 16
The Ring

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Get Handler (FSM)
client
Riak
Coordinating node
Cluster
6 7 8 9 10 11 12 13 14 15 16
The Ring

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Get Handler (FSM)
client
Riak
Coordinating node
Cluster
6 7 8 9 10 11 12 13 14 15 16
The Ring
R=2

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Get Handler (FSM)
client
Riak
Coordinating node
Cluster
6 7 8 9 10 11 12 13 14 15 16
The Ring
R=2 obj

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Get Handler (FSM)
client
Riak
R=2 obj obj

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Get Handler (FSM)
client
Riak
R=2 obj
obj

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obj

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Read Repair
(Anti-Entropy)

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replica replica replica

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X

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Active Anti-Entropy
(self healing clusters)

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real-time updates
persistent
non-blocking
disk-based

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merkle tree to track changes
coordinated at the vnode level
runs as a background process
exchange with
neighbor vnodes for inconsistencies
resolution semantics:
trigger read-repair

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= hashes marked dirty

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= keys to read-repair

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Riak and Consistency

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Riak Object

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BKey Value

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Consistent hashing; dynamic membership
Data Placement

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Replication per-value across ring
Data Placement

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Replica Replica Replica

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High Availability
…any non-failing node can respond to any request
Gilbert & Lynch

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Eventual Consistency
Eventual consistency is a consistency model used in
distributed computing that informally guarantees that, if no
new updates are made to a given data item, eventually all
accesses to that item will return the last updated value.
Wikipedia

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Take the form: {Writer, Value, Time}
Concurrent writes

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[{a, v1, t1}] [{b, v1, t2}] [{a, v1, t1}]
Concurrent writes

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[{a, v1, t1}] [{b, v1, t2}] [{a, v1, t1}]
[{b, v1, t2}] [{b, v1, t2}] [{b, v1, t2}]
Last Writer Wins

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[{a, v1, t1}] [{b, v1, t2}] [{a, v1, t1}]
[[{a, v1, t1}, {b, v1, t2}] [[{a, v1, t1}, {b, v1, t2}] [[{a, v1, t1}, {b, v1, t2}]
Allow Mult

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User specificed
Merge

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Two Approaches

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Strong
Eventual Consistency

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Designed for convergence; allows divergence
Conflict-free Replicated Data Types

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Strong
Consistency

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Provides atomicity and recency
Strong Consistency

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Prohibits partial writes
Strong Consistency

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A A A

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A A A
Val = B

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B A A

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B A A
Get Operation with Read Repair

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B A A
Get Operation with Read Repair
B B

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Single key atomic operations
Strong Consistency

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Requires read/modify/write cycle (CAS)
Strong Consistency

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Consensus

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Distributed Consensus
The problem of reaching agreement among remote
processes is one of the most fundamental problems in
distributed computing and is at the core of many
algorithms for distributed data processing,
distributed file management, and fault-tolerant
distributed applications.
Fischer, Lynch, Paterson

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Termination, agreement, validity
The Consensus Problem

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All processes eventually decide on a value
Termination

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All processes decide on the same value
Agreement

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Value decided on had to have been proposed
Validity

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Consensus Algorithms

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Paxos, ZAB, Raft, etc.
Consensus Algorithms

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Coordinated requests with a chosen leader
The Paxos Algorithm

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Node 1 Node 2 Node 3
N++ prepare(N)
promise(N, Vb) promise(N, Vc)
Vn = f(Va, Vb, Vc) commit(N, Vn)
accept(N)

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First request
Multi-Paxos

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N++; I = 0 prepare(N, I)
promise(N, I, Vb) promise(N, I, Vc)
Vn = f(Va, Vb, Vc) commit(N, I, Vn)
accept(N, I)

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Each additional request
Multi-Paxos

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I++ commit(N, I, V)
accept(N, I)

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Ship entire state!
Multi-Paxos

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Riak

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Key-value store; keys are independent state
Riak

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Multi-Paxos per key; CAS on isolated state
Riak

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Consensus Groups

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Participants in decisioning; ensembles
Consensus Groups

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Use the preference list!
Consensus Groups

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preflist

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One ensemble per preference list; ring size
Consensus Groups

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Ensembles

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election of leader; get/put operations
Riak Ensembles

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read local; refresh, if old
Get Operations

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obj.epoch < epoch get(key)
reply(Epochb, Seqb, Valb)
Val = latest(Vala, Valb, Valc)
Val.epoch = epoch
write(Epoch, ++Seq, Val)
ack(Epoch, Seq)
reply(Epochc, Seqc, Valc)

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obj.epoch == epoch
Reply = local_get(Key)

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Worst Case: 2 roundtrips / write
Get Operations
Best Case: 0 roundtrips / write

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read local; refresh, modify and commit if old
Put Operations

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obj.epoch < epoch get(key)
reply(Epochb, Seqb, Valb)
Latest = latest(Vala, Valb, Valc)
Val = modify(Latest)
ack(Epoch, Seq)
reply(Epochc, Seqc, Valc)

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obj.epoch == epoch
Latest = local_get(Key)
Val = modify(Latest)
ack(Epoch, Seq)

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Worst Case: 2 roundtrips / write
Put Operations
Best Case: 1 roundtrips / write

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Elect a new leader; start a new epoch
Failed Quorums

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Cluster Membership

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Use joint consensus from multi paxos
Dynamic Membership

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Existing Ensemble Joining Ensemble
riak_01
riak_02
riak_03
riak_07
riak_08
riak_09
[{riak_01}, {riak_02}, {riak_03}] [{riak_07}, {riak_08}, {riak_09}]

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Joint-Consensus Ensemble
[{riak_01}, {riak_02}, {riak_03}, {riak_07}, {riak_08}, {riak_09}]

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New Ensemble
riak_07
riak_08
riak_09
[{riak_07}, {riak_08}, {riak_09}]

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Distributed batch processing for Riak
MapReduce

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Data locality for map; coordinator for reduce
MapReduce

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$ curl -XPUT http://localhost:10018/buckets/training/keys/foo \
-H 'Content-Type: text/plain' \
-d 'caremad data goes here'
$ curl -XPUT http://localhost:10018/buckets/training/keys/bar \
-d 'caremad caremad caremad caremad'
$ curl -XPUT http://localhost:10018/buckets/training/keys/baz \
-d 'nothing to see here'
$ curl -XPUT http://localhost:10018/buckets/training/keys/bam \
-d 'caremad caremad caremad'
Create some objects; http://docs.basho.com/riak/latest/dev/using/mapreduce/

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> ReFun = fun(O, _, Re) ->
case re:run(riak_object:get_value(O), Re, [global]) of
{match, Matches} -> [{riak_object:key(O), length(Matches)}];
nomatch -> [{riak_object:key(O), 0}]
end
end.
> {ok, Re} = re:compile("caremad").
> {ok, Riak} = riakc_pb_socket:start_link("127.0.0.1", 8087).
> riakc_pb_socket:mapred_bucket(Riak, <>,
[{map, {qfun, ReFun}, Re, true}]).
Run Erlang MapReduce; http://docs.basho.com/riak/latest/dev/using/mapreduce/

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Distributed secondary indexing over values
Secondary Indexes (2i)

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Requires LevelDB or memory backend

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Tag objects; perform equality or range queries

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$ curl -XPOST localhost:8098/types/mytype/buckets/users/keys/
john_smith \
-H 'x-riak-index-twitter_bin: jsmith123' \
-H 'x-riak-index-email_bin: [email protected]' \
-H 'Content-Type: application/json' \
-d '{"userData":"data"}'
Create values with secondary index tags; http://docs.basho.com/riak/latest/dev/using/2i/

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$ curl http://localhost:10018/buckets/users/index/twitter_bin/
jsmith123
Query secondary index; http://docs.basho.com/riak/latest/dev/using/2i/

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Riak integration with Solr Distributed Search
Riak Search

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Schemas explain how to index fields
Riak Search Components

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Indexes are built and queried against

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Bucket-Index associations say when to index

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Default schema covers many content-types

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$ curl -XPUT http://localhost:10018/search/index/famous
Create default index using default schema; http://docs.basho.com/riak/latest/dev/using/search/

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$ curl -XPUT http://localhost:10018/search/index/famous \
-d '{"schema":"_yz_default"}'
Create default index using default schema; http://docs.basho.com/riak/latest/dev/using/search/

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$ riak-admin bucket-type create animals '{"props":{}}'
$ riak-admin bucket-type activate animals
Create bucket type for search; http://docs.basho.com/riak/latest/dev/using/search/

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$ curl -XPUT http://localhost:10018/types/animals/buckets/cats/props \
-d '{"props":{"search_index":"famous"}}'
Associate bucket, bucket type, and index; http://docs.basho.com/riak/latest/dev/using/search/

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$ curl -XPUT http://localhost:10018/types/animals/buckets/cats/keys/liono \
-d '{"name_s":"Lion-o", "age_i":30, "leader_b":true}'
$ curl -XPUT http://localhost:10018/types/animals/buckets/cats/keys/cheetara \
-d '{"name_s":"Cheetara", "age_i":28, "leader_b":false}'
$ curl -XPUT http://localhost:10018/types/animals/buckets/cats/keys/snarf \
-d '{"name_s":"Snarf", "age_i":43}'
$ curl -XPUT http://localhost:10018/types/animals/buckets/cats/keys/panthro \
-d '{"name_s":"Panthro", "age_i":36}'
Store some values; http://docs.basho.com/riak/latest/dev/using/search/

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$ curl “http://localhost:10018/search/query/famous?
wt=json&q=name_s:Lion*” | jsonpp
$ curl “http://localhost:10018/search/query/famous?wt=json&q=age_i:
%5B30%20TO%20*%5D” | jsonpp
$ curl “http://localhost:10018/search/query/famous?
wt=json&q=leader_b:true%20AND%20age_i:%5B25%20TO%20*%5D” | jsonpp
Perform search queries; http://docs.basho.com/riak/latest/dev/using/search/

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Single-key linearizability; reduced availability
Strong Consistency

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$ riak-admin bucket-type create strongly_consistent \
‘{"props":{"consistent":true}}'
$ riak-admin bucket-type status strongly_consistent
$ riak-admin bucket-type activate strongly_consistent
Enable strong consistency; http://docs.basho.com/riak/latest/dev/advanced/strong-consistency/

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Read and write a value to SC bucket
Exercise

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Conflict-Free Replicated Data Types
Strong Eventual Consistency

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Converge correctly under concurrent ops *
Strong Eventual Consistency
* See the next talk from Annette Bieniusa!

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$ riak-admin bucket-type create maps \
'{"props":{"datatype":"map"}}'
$ riak-admin bucket-type create sets \
'{"props":{"datatype":"set"}}'
$ riak-admin bucket-type create counters \
‘{“props":{"datatype":"counter"}}'
$ riak-admin bucket-type status maps
$ riak-admin bucket-type activate maps
Create bucket type for data types; http://docs.basho.com/riak/latest/dev/using/data-types/

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$ curl -XPOST http://localhost:10018/types/counters/buckets/counters/
datatypes/traffic_tickets \
-H "Content-Type: application/json" \
-d '{"increment": 1}’
$ curl http://localhost:10018/types/counters/buckets/counters/
datatypes/traffic_tickets
Operate on counters; http://docs.basho.com/riak/latest/dev/using/data-types/

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$ curl -XPOST http://localhost:10018/types/sets/buckets/travel/
datatypes/cities \
-d '{"add_all":["Toronto", “Montreal"]}'
$ curl -XPOST http://localhost:10018/types/sets/buckets/travel/
datatypes/cities \
-d '{"remove": “Montreal"}'
$ curl http://localhost:10018/types/sets/buckets/travel/datatypes/
cities
Operate on sets; http://docs.basho.com/riak/latest/dev/using/data-types/

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$ curl -XPOST http://localhost:10018/types/maps/buckets/customers/
datatypes/ahmed_info \
-d '
{
"update": {
"first_name_register": "Ahmed",
"phone_number_register": "5551234567"
}
}'
$ curl -XPOST http://localhost:8098/types/maps/buckets/customers/
datatypes/ahmed_info \
-d '
{
"update": {
"annika_info_map": {
"update": {
"interests_set": {
"add": "tango dancing"
}
}
}
}
}
' Operate on maps; http://docs.basho.com/riak/latest/dev/using/data-types/

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Read and write a value to map
Exercise

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Questions?

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Introduction to Riak

Introduction to Riak

Christopher Meiklejohn

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