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Why SQL?
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Streaming Storage
Map
Reduce
NoSQL
SQL
Database
SELECT ...
Application
Application
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SQL databases are
general-purpose data platforms
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but SQL doesn’t scale
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but SQL doesn’t scale
SQL is hard to scale
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FROM table R
SELECT x Project
x
(R) → R’
WHERE f(x) Filter
f(x)
(R) → R’
… JOIN … R × S → R’
SQL ↔ Relational Algebra
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FROM sharded_table Collect(R
1
,R
2
,...) → R’
Distributed Relational Algebra
R
1
R
2
C
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Project
x
(Collect(R
1
,R
2
,...)) = Collect(Project
x
(R
1
), Project
x
(R
2
)...)
Commutative property
R
1
R
2
C
R
1
R
2
C
P
x
P
x
P
x
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Collect(R
1
,R
2
,...) × Collect(S
1
,S
2
,...) = Collect(R
1
× S
1
,R
2
× S
2,
...)
Distributive property
R
1
R
2
C
×
C
S
1
S
2
R
1
R
2
C
×
S
1
S
2
×
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SELECT sum(price) FROM orders, nation
WHERE orders.nation = nation.name AND
orders.date >= '2017-01-01' AND
nation.region = 'Asia';
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No content
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No content
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No content
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SELECT sum(intermediate_col)
FROM ;
SELECT sum(price)
FROM orders_2 JOIN nation_2
ON (orders_2.name = nation_2.name)
WHERE
orders_2.date >= '2017-01-01'
AND
nation_2.region = 'Asia';
SELECT sum(price)
FROM orders_2 JOIN nation_1
ON (orders_2.name = nation_1.name)
WHERE
orders_2.date >= '2017-01-01'
AND
nation_2.region = 'Asia';
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Executing Distributed SQL
SQL database
orders_1
nation_1
orders
nation SELECT sum(price)
FROM orders_2 o JOIN nation_1
ON (o.name = n.name)
WHERE o.date >= '2017-01-01'
AND n.region = 'Asia';
SELECT sum(price)
FROM orders_1 o JOIN nation_1
ON (o.name = n.name)
WHERE o.date >= '2017-01-01'
AND n.region = 'Asia';
SELECT sum(price) FROM ;
SQL database
orders_2
nation_1
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Why PostgreSQL?
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PostgreSQL
Planner
Executor
Custom scan
Commit / abort
Extension (shared library)
Access methods
Foreign tables
Functions
...
...
...
...
...
...
...
SELECT ... CREATE EXTENSION ...
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PostgreSQL PostgreSQL
PostgreSQL
shards
shards
shard
shards
shards
shard
SELECT … FROM distributed_table …
SELECT … FROM shard… SELECT … FROM shard…
Citus
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PostgreSQL
Citus
PostGIS PL/Python
JSONB
2PC
Replication
...
Sequences
Indexes
Full-Text Search
Transactions
…
dblink
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PostgreSQL is becoming an extensible,
scalable general-purpose data platform