Abstractions

"Project": each is described by a URL.
Each has its own database and control server.

"Application": a particular program.
A project may have several applications.

"Account": each user has a separate account with each project.
Each account has a unique email address and a server-assigned authenticator.

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Client files
two files:

account.xml
    list of projects; for each:
        user ID
        password
    preferences

client_state.xml
    hostid
    rpc_seqno (per project)
    files, WUs, results etc.

NOTE: to "clone" an installation on a new computer,
just need to copy the core client (or run the installer)
then copy the account.xml file.

NOTE: a scheduler request can specify that no client_state.xml
was found, so a new host record should be created.
If a scheduler gets a request with an unexpected seqno,
it sends back a reply saying
--------------------
When does client contact scheduling server?
Each result has a max notification delay,
so when a client completes it there's a deadline for notification.

Contact a scheduling server if:
- you're below the low-water mark in work for that project,
  or you have a result past its deadline
- AND there's no delay in effect for that project.
    A delay may be explicitly returned by the scheduling server,
    or may be because of exponential backoff after failed attempts.
--------------------
Given that we can estimate the time it will take to get back
a result from a given host, it might be possible to assign
deadlines to results, and only send them to hosts that are fast enough
--------------------
Client logging
write events to log file:
    start/stop client
    start/finish file xfer
    start/finish application execution
    start/finish scheduling server call
    error messages

logging flag is part of preferences
--------------------
division between database and XML
proposal: move as much info as possible out of the DB into XML files.
examples:
- workunits and results
    WUs and results are described by XML files listing
    their inputs, outputs, etc.
    The DB entry for a WU contains only info relevant to scheduling:
        memory/disk/communication requirement
- user info
    A configuration is an XML file, opaque to the scheduling server
    
--------------------
WUs and results
- WUs and results are desribed by XML files that describe their
    input and output files.
- each client computation is represented by a "result" DB record,
    which is created BEFORE the client requests it.
    The application server system must keep the DB supplied
    with result records, or clients will starve.

    NOTE: this is necessary to control where output files go.
    Could also have a scheme where each application has a
    "template" result file.
    This instructs the client to create its own output file names.
    When the client returns the result,
    the server creates the result record and plugs in file names.
--------------------
File info
    input files
        "sticky": don't delete after result done
        URL (if not already on client)
    output files
        "sticky": don't delete after result done
        URL (optional; send here after result done)
--------------------
file xfer commands
    implemented as WU/result pairs whose app is "file_xfer".
    Can have just one input file, one output.
    Application servers can leaves these in a "message" directory,
    where the scheduling server can find them and give to
    client next time they contact.
--------------------
result states in client
    don't have files yet
    have files, not started
    have files, started
    completed, sending output files
    output files sent
    output files sent, some sticky files deleted

--------------------
result attributes in DB, sched server
    state:
        unsent
        sent, in progress
        timed out
    file state
        all output files are openly available
        (i.e. have been uploaded)

WU attributes in DB, sched server
    input file state (set by app server)
        all input files are available
        not all input files available

--------------------
Workunit affinity

This mechanism allows a sequence of WUs to get executed on the same host,
but allows the sequence to migrate (or be duplicated) if needed.

result attributes:
previous_resultid
    This result is a "successor" to the previous one.
    If all the sticky input and output files of the previous WU are present,
    this WU can be executed efficiently.
has_successor
    This result has a successor.

How it works:
The project generates a sequence of WUs,
each with one or more results.
It chains the results together into sequences.

When a client completes a result with successor,
it retains the result record.

NOTE: one goal of this design is to avoid the scheduler
having to know about individual files
--------------------
Scheduler request

The client sends all its results with successors

scheduler algorithm:
    if there any results with predecessors
    for which the client has all sticky files,
    send them in preference to any other results



--------------------
database tables

application
platform
app_version
core_version
account
file
workunit
    applicationid
    file1 name1
    file2 name2
    nresults
result
    workunitid
    accountid
    fileid
    boolean verified
host
--------------------
State maintained on client
Config file (XML)

<config>
    <update-time>123123</update-time>
        // last time user added project or changed CPU shares
    <max-disk-mb>1000</max-disk-mb>
    <min-work-hrs>10</min-work-hrs>
        // if estimated work falls below this, try to get more
    <max-work-hrs>10</max-work-hrs>
        // don't get more work if estimate is above this
    <max_ram_while_user_active>20</max_ram_while_user_active>
        // zero means don't work while user active
    <projects>
        <project>
            <url>http://wjwjwj</url>
            <dont-contact-until>123123</dont_contact_until>
            <control-server>blah.blah</control-server>
            </control-server>blah.blah</control-server>
            <cpu-share>1</cpu-share>
            <max-disk-mb>100</max-disk-mb>
            <cpu-total>5.44</cpu-total>
                // this is zeroed out each time shares updated
            <password>123123123</password>
                // stored on client only; not sent to server in general
            <email-address>foo@bar</email-address>
            </home-project>

            <file>
                <md5>sfkjf</md5>
                <url>akdjsfd</url>
                <size>123123</size>
                <complete/>
            </file>
            <workunit>
                <name>skdjf</name>
                <file>
                    <name>foo</name>
                    <appname>blah</appname>
                        // name by which app refers to file
                </file>
            </workunit>
            <result>
                <workunit-name>12938</workunit-name>
            <result>
        </project>
        ...
    </projects>
</config>

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Security notes:
--------------------
Client directory structure
top-level dir
    project dir (one per project)
    CPU dir (one per CPU)
        contains symbolic links to application file,
        all input and output files
--------------------
Client logic
    ["network xfer" object encapsulates a set of file xfers in progress]
    ["processor" object: one for each CPU]

    read config file
    loop
        check user activity - turn off computations if needed
        start a computation if possible
            all necessary files present,
            and workunit not done or in progress.
        check processes (fail, done)
        start new network xfers if possible
        xfer 16KB if possible (use select)
            if xfer complete, update state
        if estimated work below low-water mark
            while estimated work below high-water mark
                pick project with work due, OK dont_contact_until
                contact a control server; request high-current work
                if can't get connection, update dont_contact_until
            end
        end
    end
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Application logic
--------------------
Control RPC protocol
--------------------
Web site functions
--------------------
Startup scenarios

- How a user initially signs up:
Visit the project's URL.
Create an account:
    enter email address
    wait for password to arrive in email.
    download installer
    installer installs agent, initial config file
    run agent; type in password.

- How a user adds a project
Same as above, but don't download agent.
Go to "home" web site and add project.

- How a user removes a project
Go to "home" web site and remove project

------------------------------
Versions

Core client:

When and how does a scheduler tell a core agent
that a newer version can/should be downloaded?

How is compatibility between application agents
and core agents represented?
--------------------------------------
Distributed storage

Projects can use clients for storage using "sticky" files
(which are either sent to clients, or generated by the client).

The core client is free to delete sticky files any time.

Scheduler requests include a list of the sticky files held by the host.
This list is stored in a blob in the host record.

Scheduler replies can include <file_info> tags
instructing the client to download files.
These files need not be associated with applications or workunits.

Scheduler replies can include <file_info> tags
instructing the client to upload

--------------------------------
Preferences

CPU usage
    don't run or communicate if on batteries
    don't run or communicate if user is active
    confirm before making network connection
    minimum, maximum work buffer

Disk usage
    use at most X GB
    leave at least X GB free
    leave at least X% free

Projects
    For each project:
        master URL
        email address
        authenticator
        resource %
        show email address on web site?
        accept emails from project?
        project-specific prefs