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
>
>
>
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