Thanks for the responses.
Raph, thank you again. I very much appreciate your "humble offering".
I'll take a further look into your gist.
Steven, I'm happy to use the right tool for the job...so long as I have an
idea of what it is. Would you care to offer more insights or suggestions
for the ill-informed (such as myself)?
---Zachary
On Sunday, October 16, 2016 at 7:51:19 AM UTC-4, Steven Sagaert wrote:
>
> 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
>>>>
>>>
