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I don't quite get why SQLite is the right primitive to compose a large scale database system out of... If the design goal is write throughput, SQLite can be be

I don't quite get why SQLite is the right primitive to compose a large scale database system out of... If the design goal is write throughput, SQLite can be beat really easily by the client/server systems since each SQLite instance only supports one concurrent writer. I guess users of Bedrock could partition their datasets into different pieces that aren't often written in tandem, but why go through all the trouble instead of just using a database with real MVCC? If the design goal is geo replication, Bedrock seems to ignore the past many years of innovation in the field. MySQL and company have methodically built up features to allow safe synchronous and asynchronous replication for minimizing the risk of downtime or data loss like GTIDs over a long time If the design goal is read throughput, I don't think Bedrock can be faster than just pure SQLite if your data can live beside your application, and if you have more than one node, you need a complicated SQL optimizer that understands how to push down things like predicates and aggregates to the leaves, and then recombine results at the top level to actually efficiently read in parallel, which I don't think Bedrock has built yet. This thing kind of seems reminiscent of Jetpants or one of the other MySQL orchestration tools that allow for scaling the DB beyond many nodes automatically... but... why SQLite?

quinthar 10y ago
Thanks for asking! Re: "SQLite can be beat really easily by the client/server systems since each SQLite instance only supports one concurrent writer" -- That's not actually true, sqlite supports concurrent writers via their page-locking branch (and changesets allow for effectively row-level locks). But none of that matters, because single-threaded replication means any multi-threaded write capability is irrelevant. Regardless, when we add multi-threaded replication (on the way), we'll take advantage of SQLite's multi-thread write capabilities. Re: MySQL's replication. What specifically are you referring to? It's distributed transaction features are actually quite new -- and I think were developed after Bedrock was already in production for years. Furthermore, MySQL doesn't support automatic master failover (or recovery), and struggles over high-latency, low-reliability WAN connections. Anyway, if I'm wrong on any of that, I'm eager to be corrected. Thanks! Re: Read throughput. Agreed it doesn't have "parallel reads" (eg, it doesn't split a large read up into multiple smaller reads that are joined automatically). However, I don't think MySQL does either. Regardless, Bedrock does quite well for normal read queries, and uses all of the node's CPUs efficiently. (To be clear, I love this idea of adding "super threaded reads", and have some ideas. But at the moment we don't have any application that requires it, so haven't built it.) Re: Jetpants, I haven't heard of that before. Thanks for the tip! But as for why SQLite over MySQL, I'd ask quite the opposite: why add a networked layer on top of MySQL, thereby ignoring all of MySQL's networking? That just adds all the overhead of MySQL, without any of the benefit. If you're going to build a networking layer atop a database, SQLite seems the clear choice because it is explicitly designed to be a database library -- and not a database server. Thanks for all these comments!
- chucky_z 10y ago
  Automatic failover -- https://dev.mysql.com/doc/mysql-utilities/1.5/en/mysqlfailover.html https://dev.mysql.com/doc/mysql-utilities/1.5/en/mysqlfailov... Guides to doing auto failover and recovery: https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-autofailover.html https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-... https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-restore-master.html https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-...
  - quinthar 10y ago
    Cool, thanks! It looks like that came out in 2012? Neat, I'll take a look!
    - quinthar 10y ago
      Incidentally, if anybody has experience with this I'd love to know: 1) What happens if "mysqlfailover" itself dies? For example, if I have 6 servers split equally between 2 datacenters, and the datacenter running mysqlfailover loses power -- how does the other datacenter get reconfigured? 2) If you run two copies of mysqlfailover (one in each datacenter), how does it solve the "split brain" problem? If you have 6 servers split equally between two datacenters, and a clean network severance down the middle, what prevents both sides from configuring and operating a master? (This is the nightmare scenario.) 3) If mysqlfailover dies, it sounds like it will prevent any other copy from running without manual intervention: "At startup, the console will attempt to register itself with the master. If another console is already registered, and the failover mode is auto or elect, the console will be blocked from running failover. When a console quits, it unregisters itself from the master. If this process is broken, the user may override the registration check by using the --force option." Overall, this sounds like a great improvement over what existed before (eg, nothing), but still a pretty brittle, manual, and (in the case of split-brain) very dangerous approach. Have you had good experience with it in practice?
      - brusch64 10y ago

quinthar 10y ago

Thanks for asking! Re: "SQLite can be beat really easily by the client/server systems since each SQLite instance only supports one concurrent writer" -- That's not actually true, sqlite supports concurrent writers via their page-locking branch (and changesets allow for effectively row-level locks). But none of that matters, because single-threaded replication means any multi-threaded write capability is irrelevant. Regardless, when we add multi-threaded replication (on the way), we'll take advantage of SQLite's multi-thread write capabilities. Re: MySQL's replication. What specifically are you referring to? It's distributed transaction features are actually quite new -- and I think were developed after Bedrock was already in production for years. Furthermore, MySQL doesn't support automatic master failover (or recovery), and struggles over high-latency, low-reliability WAN connections. Anyway, if I'm wrong on any of that, I'm eager to be corrected. Thanks! Re: Read throughput. Agreed it doesn't have "parallel reads" (eg, it doesn't split a large read up into multiple smaller reads that are joined automatically). However, I don't think MySQL does either. Regardless, Bedrock does quite well for normal read queries, and uses all of the node's CPUs efficiently. (To be clear, I love this idea of adding "super threaded reads", and have some ideas. But at the moment we don't have any application that requires it, so haven't built it.) Re: Jetpants, I haven't heard of that before. Thanks for the tip! But as for why SQLite over MySQL, I'd ask quite the opposite: why add a networked layer on top of MySQL, thereby ignoring all of MySQL's networking? That just adds all the overhead of MySQL, without any of the benefit. If you're going to build a networking layer atop a database, SQLite seems the clear choice because it is explicitly designed to be a database library -- and not a database server. Thanks for all these comments!

chucky_z 10y ago
Automatic failover -- https://dev.mysql.com/doc/mysql-utilities/1.5/en/mysqlfailover.html https://dev.mysql.com/doc/mysql-utilities/1.5/en/mysqlfailov... Guides to doing auto failover and recovery: https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-autofailover.html https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-... https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-restore-master.html https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-...
- quinthar 10y ago
  Cool, thanks! It looks like that came out in 2012? Neat, I'll take a look!
  - quinthar 10y ago
    Incidentally, if anybody has experience with this I'd love to know: 1) What happens if "mysqlfailover" itself dies? For example, if I have 6 servers split equally between 2 datacenters, and the datacenter running mysqlfailover loses power -- how does the other datacenter get reconfigured? 2) If you run two copies of mysqlfailover (one in each datacenter), how does it solve the "split brain" problem? If you have 6 servers split equally between two datacenters, and a clean network severance down the middle, what prevents both sides from configuring and operating a master? (This is the nightmare scenario.) 3) If mysqlfailover dies, it sounds like it will prevent any other copy from running without manual intervention: "At startup, the console will attempt to register itself with the master. If another console is already registered, and the failover mode is auto or elect, the console will be blocked from running failover. When a console quits, it unregisters itself from the master. If this process is broken, the user may override the registration check by using the --force option." Overall, this sounds like a great improvement over what existed before (eg, nothing), but still a pretty brittle, manual, and (in the case of split-brain) very dangerous approach. Have you had good experience with it in practice?
    - brusch64 10y ago