copy/fork running kdb+ instance

Community Support
1

Hi,I want to be able to do the following:1. Start a single instance of KDB2. Execute typical data transactions KDB instance 13. At a specific time during the day, start KDB instance 24. At that same time, COPY the entire executing data entity value set@KDB instance 1 to @KDB instance 25. @ KDB instance 1, continue processing transactions (not copy?g anymore data to @KDB instance 2)6. @ KDB instance 2 process new, separate transactions (never copy?gany data ever to @KDB instance 1)I basically want to do a DNA/KDB+ ?fork/exec? ? what is best way to dothis?

2

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Date: Sun, 31 Oct 2010 09:35:28 -0400
To: “personal-kdbplus@googlegroups.com”

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Hi Ben,

DNA is a Citi specific implementation so can’t help with doing it that way, b=
ut keep in mind any constant copying (ie large amounts of data) you do from=
q to q will halt a q process because it’s single threaded. Multi-threading i=
s out of the question. (hence DNA’s raison d’=C3=AAtre)

The only way around locking up both q processes is via replay-able log files=
a la -11! with a count specified.

Tim

3

I think that needs clarifying further.

kdb+ in single threaded mode sends as much data as the tcp connection can absorb, and then backs off to continue processing other input, resuming any pending sends later.

A receiving q process that issued a sync request and is awaiting a response will block until that response is received in full.

Blocking can be circumvented by using async messaging; however an applications required behavior may not allow such interleaving.

4

X-Mailer: Apple Mail (2.936)

you can retrieve everything in the root space by getting `.

be aware of the timing considerations charlie and timothy mentioned tho

$ q -p 5050
q)a:1
q)b:`foo
q)c:(x:())

$ q
q). upsert hopen[5050].
. q)a 1 q)b foo
q)c
x

5

One option would be to write a q plug in module in C and implement the q fork function.

regards,

Junan

6

Junan, if you’re referring to the fork system call, this will segfault q. If you mean something else, please elaborate.

7 
something like the following, I didn't try, but why will it segfault q?

# **include**** \<k.h\>**


K q_fork(K x)
{
int pid = fork();
**return** ki(pid);
}
8

qfork:qfork 2:(q_fork;1)
q)qfork 1
13178
q)0
q)\

q)\

I compiled the code and test it. the fork succeeded with no segfault.?

regards.

Junan