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" <[email protected]> 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 <[email protected]>:
> 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" <[email protected]> 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
> <[email protected]> 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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