that because SQLLite isn't a multi-user DB server but a single user
embedded (desktop) db. Use the right tool for the job.
On Saturday, October 15, 2016 at 7:02:58 PM UTC+2, Ralph Smith wrote:
>
> How are the processes supposed to interact with the database? Without
> extra synchronization logic, SQLite.jl gives (occasionally)
> ERROR: LoadError: On worker 2:
> SQLite.SQLiteException("database is locked")
> which on the face of it suggests that all workers are using the same
> connection, although I opened the DB separately in each process.
> (I think we should get "busy" instead of "locked", but then still have no
> good way to test for this and wait for a wake-up signal.)
> So we seem to be at least as badly off as the original post, except with
> DB calls instead of simple writes.
>
> We shouldn't have to stand up a separate multithreaded DB server just for
> this. Would you be kind enough to give us an example of simple (i.e. not
> client-server) multiprocess DB access in Julia?
>
> On Saturday, October 15, 2016 at 9:40:17 AM UTC-4, Steven Sagaert wrote:
>>
>> It still surprises me how in the scientific computing field people still
>> refuse to learn about databases and then replicate database functionality
>> in files in a complicated and probably buggy way. HDF5 is one example,
>> there are many others. If you want to to fancy search (i.e. speedup search
>> via indices) or do things like parallel writes/concurrency you REALLY
>> should use databases. That's what they were invented for decades ago.
>> Nowadays there a bigger choice than ever: Relational or non-relational
>> (NOSQL), single host or distributed, web interface or not, disk-based or
>> in-memory,... There really is no excuse anymore not to use a database if
>> you want to go beyond just reading in a bunch of data in one go in memory.
>>
>> On Monday, October 10, 2016 at 5:09:39 PM UTC+2, Zachary Roth wrote:
>>>
>>> Hi, everyone,
>>>
>>> I'm trying to save to a single file from multiple worker processes, but
>>> don't know of a nice way to coordinate this. When I don't coordinate,
>>> saving works fine much of the time. But I sometimes get errors with
>>> reading/writing of files, which I'm assuming is happening because multiple
>>> processes are trying to use the same file simultaneously.
>>>
>>> I tried to coordinate this with a queue/channel of `Condition`s managed
>>> by a task running in process 1, but this isn't working for me. I've tried
>>> to simiplify this to track down the problem. At least part of the issue
>>> seems to be writing to the channel from process 2. Specifically, when I
>>> `put!` something onto a channel (or `push!` onto an array) from process 2,
>>> the channel/array is still empty back on process 1. I feel like I'm
>>> missing something simple. Is there an easier way to go about coordinating
>>> multiple processes that are trying to access the same file? If not, does
>>> anyone have any tips?
>>>
>>> Thanks for any help you can offer.
>>>
>>> Cheers,
>>> ---Zachary
>>>
>>
