And final update…
It turns out that ExecuteSql doesn’t distribute processing across the nodes in
the cluster – not unsurprising really when I think about it, so refinement to
the below was to just have the text file on one node so that it effectively
only runs on that node. Of course I could have set the ExecuteSql processor
just to run on Primary Node but I fear that that node would become overloaded
as I have a bunch of other stuff that runs on there exclusively.
I don’t know if on roadmap, but would be useful to be able to indicate for a
processor to run on any specific node in cluster other than just primary (so a
manual load balancing could be under control of user). I think this has been
discussed before though).
Conrad
On 05/08/2016, 15:35, "Conrad Crampton" <conrad.cramp...@secdata.com> wrote:
Thanks for the input on this.
As a follow-up this is what I have done…
Created a text file which contains single value of the lowest ID of the
data I am retrieving, save on each node of cluster.
Then
GetFile (to read file)
ExtractText (to get the value – and set to attribute)
UpdateAttribute (to create another attribute which is the upper bound of
the ID to use in sql i.e. lower >= ID < upper)
ExecuteSql (using the attribute as above as parameters) – using DBPool for
connection
Branch1
MergeContent
PutHDFS
Branch2
ReplaceText (replace flowfile content with upper attribute from above)
PutFile (same filename as came in)
Rinse…Repeat
Appears to be working ok. Issue is that if ExecuteSQL fails, then as I have
it now, the file is original deleted – probably better to get this moved so
always have a backup of the last id used.
Conrad
On 03/08/2016, 15:34, "Yohann Lepage" <yoh...@lepage.info> wrote:
Hi,
I have exactly the same use case to periodically get rows from some
security appliances with just a read only access.
Currently (without NiFi), we use an SQL query to track the maximum
value, depending on the DB/appliance/vendor, it could be a simple
"SELECT getdate()" or "select max(SW_TIME) from log_table" or a more
complex query with INNER JOIN.
So, it would be great to have an option to customize the tracking query.
Regards
2016-08-03 16:02 GMT+02:00 Conrad Crampton
<conrad.cramp...@secdata.com>:
> Hi,
> Thanks for this.
> I did think about a MV but unfortunately I haven’t access to create
views – just read access. That would have been my simplest option ;-) Life’s
never that easy though is it?
> The only part of the sql I need to be dynamic is the date parameter
(I could even use the id column). Instead of using the MapCache (if that isn’t
a good idea), could I use the GetFile to just pull a single txt file with the
parameter (i.e. last run or max id value from the last run), which creates
flowfile, read that value and pass that into ExecuteSql (using the
aforementioned value as the parameter in the sql) as the select query can be
dynamically constructed from attributes/ flowfile content (as per docs)? And
then finally write text file back to file system to be picked up next time?
> Thanks
> Conrad
>
> On 03/08/2016, 14:02, "Matt Burgess" <mattyb...@gmail.com> wrote:
>
> Conrad,
>
> Is it possible to add a view (materialized or not) to the RDBMS?
That
> view could take care of the denormalization and then
> QueryDatabaseTable could point at the view. The DB would take
care of
> the push-down filters, which functionally is like if you had a
> QueryDatabaseTable for each table then did the joins.
>
> In NiFi 1.0 there is a GenerateTableFetch processor which is like
> QueryDatabaseTable except it generates SQL instead of executing
SQL.
> That might be used in your a) option above but you'd have to
reconcile
> the SQL statements into a JOIN. A possible improvement to
either/both
> processors would be to add attributes for the maximum value
columns
> whose values are the maximum observed values. Then you wouldn't
have
> to parse or manipulate the SQL if you really just want the max
values.
>
> I have been thinking about how QueryDatabaseTable and
> GenerateTableFetch would work if they accepted incoming flow
files (to
> allow dynamic table names for example). It's a bit more tricky
because
> those processors run without input to get max values, so their
> behavior would change when a flow file is present but would
return to
> the original behavior if no flow file is present. Since the
> ListDatabaseTables processor is also in 1.0, it would be nice to
use
> that as input to the other two processors.
>
> I'm definitely interested in any thoughts or discussion around
these things :)
>
> Regards,
> Matt
>
> On Wed, Aug 3, 2016 at 8:37 AM, Conrad Crampton
> <conrad.cramp...@secdata.com> wrote:
> > Hi,
> >
> > My use case is that I want to ship a load of rows from an RDMS
periodically
> > and put in HDFS as Avro.
> >
> > QueryTable processor has functionality that would be great i.e.
maxcolumn
> > value (there are couple of columns I could use for this from
the data) and
> > it is this functionality I am looking for, BUT the data is not
from one
> > single table. The nature of the RDBMS is that the business view
on the data
> > requires a bunch of joins from other tables/schemas to get the
correct Avro
> > file so the options I appear to have are
> >
> > a) Use QueryTable for each table that make up the
business view and do
> > the joins etc. in HDFS (Spark or something) – or potentially do
the
> > reconciliation within NiFi???
> >
> > b) Use ExecuteSQL to run the complete SQL to get the rows
which can
> > easily be put into HDFS as Avro given that the line will be the
business
> > (denormalised) data that is required.
> >
> > The problem with a) is the reconciliation (denormalisation) of
the data and
> > the problem with b) is how to maintain the maxcolumn value so I
only get the
> > data since the last run.
> >
> >
> >
> > In order to address b) can I use the DistrubutedMapCacheServer
& Client to
> > hold a key/value pair of last run date and extract from this
date as a
> > parameter?
> >
> >
> >
> > Thanks for any suggestions.
> >
> >
> >
> > Conrad
> >
> >
> >
> > SecureData, combating cyber threats
> >
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