F1: A Distributed SQL Database That Scales(research.google.com)
research.google.com
F1: A Distributed SQL Database That Scales
http://research.google.com/pubs/pub41344.html
4 comments
Your point about change history and its poor support in SQL is spot-on; at my employer we've gone through (1) and (2) and are trying to figure out (3) at the moment.
From what I understand of Datomic temporal support is baked in, but it's about the only database I can think of that does that, and I haven't heard stories about it being used in production for large volumes of data.
From what I understand of Datomic temporal support is baked in, but it's about the only database I can think of that does that, and I haven't heard stories about it being used in production for large volumes of data.
Snodgrass wrote an entire book about dealing with the temporal blindness of SQL which might help you:
http://www.cs.arizona.edu/people/rts/tdbbook.pdf
More generally, you can usually build a model that handles (2), the changing state, by generalising your original model. I've done in both of classical ways, having either validity period fields (thus pushing complexity into every query), or by having audit tables (thus relying on triggers).
But building a changing model is hard, because at the schema level, SQL only supports (1). That is, it provides primitives to change the current state of the model.
So you wind up having to build a meta-model. The deficiencies of SQL (and I'm an RDBMS bigot) mean that we wind up building inner platforms. Or outer platforms -- witness migration toolkits.
Yet support for changing models is essential. No model is ever constant. Most of my work is for a public-sector client whose legal reporting requirements are constantly changing. You cannot throw away old reports which were made under old regulations; you must be able to recreate the world at any point in time. Which requires either a lot of bookkeeping code or taking periodic snapshots.
Datomic looks neat. I see that I'm not the only one who made the leap from transactional memory to transactional models.
Edit: I just found notes I wrote in 2009 on database languages while looking for something else. Spooky: http://chester.id.au/2013/08/28/notes-towards-a-set-objectiv...
http://www.cs.arizona.edu/people/rts/tdbbook.pdf
More generally, you can usually build a model that handles (2), the changing state, by generalising your original model. I've done in both of classical ways, having either validity period fields (thus pushing complexity into every query), or by having audit tables (thus relying on triggers).
But building a changing model is hard, because at the schema level, SQL only supports (1). That is, it provides primitives to change the current state of the model.
So you wind up having to build a meta-model. The deficiencies of SQL (and I'm an RDBMS bigot) mean that we wind up building inner platforms. Or outer platforms -- witness migration toolkits.
Yet support for changing models is essential. No model is ever constant. Most of my work is for a public-sector client whose legal reporting requirements are constantly changing. You cannot throw away old reports which were made under old regulations; you must be able to recreate the world at any point in time. Which requires either a lot of bookkeeping code or taking periodic snapshots.
Datomic looks neat. I see that I'm not the only one who made the leap from transactional memory to transactional models.
Edit: I just found notes I wrote in 2009 on database languages while looking for something else. Spooky: http://chester.id.au/2013/08/28/notes-towards-a-set-objectiv...
Databases which use MVCC handle (2) - and if they have transactional DDL, then they cover (3). But they don't keep the history permanently. Who wants all that old data?
The one exception to this that i know of is Oracle, which although not fashionable round here, does expose the MVCC log through "flashback queries", where one can simply write "SELECT * FROM USER AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)":
http://docs.oracle.com/cd/B28359_01/appdev.111/b28424/adfns_...
I don't know what the logistics of keeping an infinite history are. I do know that an e-commerce system i worked with before kept a few days, and that that saved our bacon on a couple of occasions.
The one exception to this that i know of is Oracle, which although not fashionable round here, does expose the MVCC log through "flashback queries", where one can simply write "SELECT * FROM USER AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)":
http://docs.oracle.com/cd/B28359_01/appdev.111/b28424/adfns_...
I don't know what the logistics of keeping an infinite history are. I do know that an e-commerce system i worked with before kept a few days, and that that saved our bacon on a couple of occasions.
They have the technological underpinnings, but it's not properly exposed via SQL. In practice you wind up having to do it all by hand.
What the F1 guys seem to have done is said "well that's just silly, let's take advantage of it".
Oracle is my day job, I've been saved by a flashback query once. A DBA misunderstood a request I was making and applied a dev change to production.
> I don't know what the logistics of keeping an infinite history are.
I'd say they're not much different than asking a database developer to be able to generate reports for any given span of time. Or keeping a complete audit trail of changes. Or, more broadly, complete website logs, complete source revision history etc etc.
That is: in theory it creates an infinite downside. In practice it is more valuable than not, especially with the ever-plunging cost of storage.
What the F1 guys seem to have done is said "well that's just silly, let's take advantage of it".
Oracle is my day job, I've been saved by a flashback query once. A DBA misunderstood a request I was making and applied a dev change to production.
> I don't know what the logistics of keeping an infinite history are.
I'd say they're not much different than asking a database developer to be able to generate reports for any given span of time. Or keeping a complete audit trail of changes. Or, more broadly, complete website logs, complete source revision history etc etc.
That is: in theory it creates an infinite downside. In practice it is more valuable than not, especially with the ever-plunging cost of storage.
PostgreSQL used to allow this via "Time Travel", but it has long since been removed (I think because it was rarely used and supporting it interfered with other optimizations.)
Also, Datomic is not open source :(
> [I] guess they've privileged this model in their storage because that's what a lot of their AdWords schema looks like.
This is actually the model they've used in things like AppEngine as well - nested entities allow them to take advantage of locality in transactions.
This is actually the model they've used in things like AppEngine as well - nested entities allow them to take advantage of locality in transactions.
How do hierarchical tables compare to Postgres' hstore?
I think recursive structures like lists and trees are one weakness of the relational model, and haven't found a fully satisfying relational answer to the limitations. It seems to me like the assumption of atomic column types is a major weakness inherent in the relational model itself when it comes to recursion. Any thoughts/comments?
I think recursive structures like lists and trees are one weakness of the relational model, and haven't found a fully satisfying relational answer to the limitations. It seems to me like the assumption of atomic column types is a major weakness inherent in the relational model itself when it comes to recursion. Any thoughts/comments?
> How do hierarchical tables compare to Postgres' hstore?
If I am reading them correctly, it's a storage strategy, not a specific "feature" per se. The closest analogy to hstore is that they provide native support for storing and querying protobuf blobs.
> I think recursive structures like lists and trees are one weakness of the relational model, and haven't found a fully satisfying relational answer to the limitations.
It depends on why you're using trees or graphs.
If it's inherent in the data, then modern SQL has recursive queries that make it much easier than the old methods.
If it's inherent in the model, you will find it harder. You might need to pick a non-standard approach, such as PostgreSQL's inherited tables. I'd think long and hard before saying it's inherent in the model, by the way. Strictly speaking you can represent the same thing as sets of relations or as a graph; it's better to utilise the strengths of the tool in front of you.
If I am reading them correctly, it's a storage strategy, not a specific "feature" per se. The closest analogy to hstore is that they provide native support for storing and querying protobuf blobs.
> I think recursive structures like lists and trees are one weakness of the relational model, and haven't found a fully satisfying relational answer to the limitations.
It depends on why you're using trees or graphs.
If it's inherent in the data, then modern SQL has recursive queries that make it much easier than the old methods.
If it's inherent in the model, you will find it harder. You might need to pick a non-standard approach, such as PostgreSQL's inherited tables. I'd think long and hard before saying it's inherent in the model, by the way. Strictly speaking you can represent the same thing as sets of relations or as a graph; it's better to utilise the strengths of the tool in front of you.
Both Oracle and Postgres have objects and collections. This allows you to build hierarchical structures.
Postgres unfortunately doesn't allow for recursive structures ;(
If you are interested in how to do it take a look here: https://blog.dsl-platform.com/postgres-bridge-between-worlds...
If you are interested in how to do it take a look here: https://blog.dsl-platform.com/postgres-bridge-between-worlds...
It should be noted that Oracle's object types are a feature of PL/SQL, their imperative programming language.
PostgreSQL's concept of object-relational databases is baked into the SQL. Into the logical model of the data itself.
Put another way: Oracle doesn't have table inheritance.
PostgreSQL's concept of object-relational databases is baked into the SQL. Into the logical model of the data itself.
Put another way: Oracle doesn't have table inheritance.
We are using Oracle object types in plain SQL, so no, they are not PL/SQL exclusive. But yeah, you can do a lot less with them outside of PL/SQL.
Right, you're right, I overlooked CREATE TABLE OF.
I posted this question on StackOverflow regarding TrueTime (used by Spanner) a few days ago and haven't received any responses:
<http://stackoverflow.com/questions/18384883/why-is-googles-t...
However, I think this HN thread seems like it might be a good place to get comments on why my line of reasoning may be incorrect. Does anyone have any thoughts on why building something like Spanner on top of basic Paxos quorums and NTP would be a bad idea?
<http://stackoverflow.com/questions/18384883/why-is-googles-t...
However, I think this HN thread seems like it might be a good place to get comments on why my line of reasoning may be incorrect. Does anyone have any thoughts on why building something like Spanner on top of basic Paxos quorums and NTP would be a bad idea?
Check this out.
http://muratbuffalo.blogspot.com/2013/08/beyond-truetime-usi...
Thanks for the link -- I'm working through it now.
Can someone enlighten me as to why google doesn't want to make an enterprise play? Many companies tout that they are offering data infrastructures similar to those used at google..why wouldn't google commercialize that technology themselves? It should be pretty obvious as to how that could be of huge financial benefit to the company.
> Can someone enlighten me as to why google doesn't want to make an enterprise play?
They do. They have a range of commercial, including enterprise, offerings (many of which are based on originally-internal technologies, including their MySQL-based distributed database that preceded F1.)
> why wouldn't google commercialize that technology themselves?
They probably will, just as they have commercialized their previous internal storage technologies.
They do. They have a range of commercial, including enterprise, offerings (many of which are based on originally-internal technologies, including their MySQL-based distributed database that preceded F1.)
> why wouldn't google commercialize that technology themselves?
They probably will, just as they have commercialized their previous internal storage technologies.
This is not new by any mean...
The paper was only published in conference proceedings yesterday.
"not new" != "not interesting"
-- Secret sauce
A lot of the magic of F1 comes from Spanner, the distributed storage system. The name "F1" itself is an allusion to "inheriting" some of the properties of Spanner.
-- Hierarchical tables
What they call hierarchical tables, I would think best be viewed as one-to-many relationships. In guess they've privileged this model in their storage because that's what a lot of their AdWords schema looks like.
-- Change History
I like the observation that keeping full histories is relatively straightforward with atomic, granular timestamping and indeed that it should be baked in. Every database schema I've ever worked with always goes through a similar evolutionary cycle:
1. We only need to capture the current state of the model.
2. Wait, we do need to capture historical states of the model.
3. Wait, the model is changed, we need to capture historical states and the models that were current.
(You can think of this as taking progressive differentials of incoming transactions).
The F1 designers have baked that right into the database, where it belongs. Weak temporal support has long been the sore point in SQL.
-- Remote data
I was struck by their observation that most database storage engines are built around the concept of seeks and reads, whereas theirs is necessarily built around batching and pipelining over a network. If I am reading them correctly, their engine takes advantage of having multiple copies of data by sending reads to multiple disk nodes and then working from the first copy that is returned.