Hmm, so far, chaning this single line seems to do the trick. I successfully
created a simple projection applying the following patch:
diff --git a/src/bord.cpp b/src/bord.cpp
index 1f2ffa5..a9c34ba 100755
--- a/src/bord.cpp
+++ b/src/bord.cpp
@@ -1859,7 +1859,7 @@ int ibis::bord::backup(const char* dir, const char* tname,
}
ibis::bitvector msk0, msk1;
- msk0.set(0, nEvents);
+ msk0.set(1, nEvents);
md << "# meta data for data partition " << tname
<< " written by bord::backup on " << stamp << "\n\n"
<< "BEGIN HEADER\nName = " << tname << "\nDescription = "
I’m really not sure of what i’m doing, but as far as i understood, msk0 is the
bitvector of the values we are supposed to write, so it seems to make sense...
John, feel free to comment/ammend this.
Thanks,
From: [email protected]
[mailto:[email protected]] On Behalf Of Dominique Prunier
Sent: Monday, January 16, 2012 3:06 PM
To: FastBit Users
Subject: Re: [FastBit-users] Convert a bundle into a partition
Hmm, maybe not... It seems that it always save NULL values, i’ll keep
investigating and keep you posted...
Thanks,
From: [email protected]
[mailto:[email protected]] On Behalf Of Dominique Prunier
Sent: Monday, January 16, 2012 2:37 PM
To: FastBit Users
Subject: Re: [FastBit-users] Convert a bundle into a partition
Hey,
I found a pretty easy way to create an on-disk projection.
ibis::table* tbl = ibis::table::create("<partition directory>");
ibis::table* sel = tbl->select("<cols>", "<where>");
ibis::table* dev = sel->groupby("<cols> ");
dev->backup("<projection directory>", "<projection name>", "<projection
description>");
It seems to do pretty much what you’d expect.
John, please tell us if this is a decently efficient way of doing it. More
specifically, i have no idea about the memory overhead of the intermediate sel
and the dev tables (does it only store a hit vector and reference the tbl table
? i see that groupby uses a bundle, but what about the dev table itself ?).
Thanks,
From: Jon Strabala [mailto:[email protected]]
Sent: Monday, January 16, 2012 1:35 PM
To: K. John Wu
Cc: Dominique Prunier
Subject: Re: [FastBit-users] Convert a bundle into a partition
John,
This might be a very usefull enhancement, e.g. imagine a system where fasbit
could a created directed permenate materialized views (manged explicitly for
say a DSS) or a alternatively a cache of materialized views from the most
recent queries.
I can image several use cases for such functionality.
Best Regards,
Jon Strabala
On Mon, Jan 16, 2012 at 7:59 AM, K. John Wu <[email protected]<mailto:[email protected]>>
wrote:
Hi, Dominique,
There is an in-memory data partition known as ibis::bord which can
take a select clause and a data partition as input argument. This
might be the closest to what you want. A little bit more work is
needed to get to where you need it.. I am out of office during the
day, might have time to look into this in the night..
John
On 1/16/12 6:25 AM, Dominique Prunier wrote:
> Hi,
>
>
>
> I was wondering if there were a way to convert a a bundle into a
> partition. My goal here would be to create some projection of my
> partition grouped by a subset of columns. For ex, my main partition
> would be:
>
>
>
> Col1 Col2 Col3
>
> 1 A B
>
> 2 C D
>
> 3 A B
>
> 4 A B
>
>
>
> And i’d like the following projection (Col2 and Col3), which is the
> result of “SELECT Col2,Col3 GROUP BY Col2,Col3”:
>
>
>
> Col2 Col3
>
> A B
>
> C D
>
>
>
> Thanks,
>
>
>
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