Thanks. We didn't specify the number of mappers, so it's giving us 4. I understand your explanation, but it seems to conflict with the Sqoop user guide ( http://sqoop.apache.org/docs/1.4.3/SqoopUserGuide.html#_controlling_parallelism ):
"When performing parallel imports, Sqoop needs a criterion by which it can split the workload. Sqoop uses a *splitting column* to split the workload. By default, Sqoop will identify the primary key column (if present) in a table and use it as the splitting column. The low and high values for the splitting column are retrieved from the database, and the map tasks operate on evenly-sized components of the total range. For example, if you had a table with a primary key column of id whose minimum value was 0 and maximum value was 1000, and Sqoop was directed to use 4 tasks, Sqoop would run four processes which each execute SQL statements of the form SELECT * FROM sometable WHERE id >= lo AND id < hi, with (lo, hi) set to (0, 250), (250, 500), (500, 750), and (750, 1001) in the different tasks." On Wed, Jun 19, 2013 at 3:14 PM, Abraham Elmahrek <[email protected]> wrote: > Hey David, > > Here's the algorithm: > Split lengths are defined by (max - min)/(# mappers) and whatever is left > is tacked on at the end. So in this case, (288272191-2110)/3 = > 96090027.33... So I'm assuming the .33... is rounded down and split lengths > will be of length 96090027. Sqoop will then create splits with the > following points: (min) + (range length)*(n). We can see that 2110 + > 96090027*0 > = 2110, 2110 + 96090027*1 = 96092137, 2110 + 96090027*2 = 192182164, and 2110 > + 96090027*3 = 288272191 will be generated based off of this algorithm. > The last point to be added will be 288272192 because the max value is not > part of the generated split points. Then sqoop will distributed accordingly > based off of these points as you've pointed out above. > > Just to be sure, did you configure sqoop to use 3 mappers? > > Hope this helps, > -Abe > > > On Wed, Jun 19, 2013 at 8:33 AM, David Kincaid <[email protected]>wrote: > >> We're seeing a strange thing happen with a sqoop import job with the way >> the key range is getting distributed among the 4 mappers that are running. >> The minimum key value is 2110 and the maximum value is 288272191. We are >> getting one mapper that is only getting one record to import. Here is the >> distribution among the mappers: >> >> [2110, 96092137) >> [96092137, 192182164) >> [192182164, 288272191) >> [288272191, 288272192) >> >> you can see that the fourth mapper is given a range with only one value >> in it. Could someone help me understand what is going on? >> >> Thanks, >> >> Dave >> > >
