Hi, I've been playing with HCatalog for the past couple weeks now, and I have a few questions regarding schemas in MR jobs.
>From what I read in the documentation, schemas are optional, and if not specified it defaults to the table level schemas. Here are some extracts from the documentation: You can use the setOutputSchema method to include a projection schema, to specify specific output fields. If a schema is not specified, this default to the table level schema. The schema for the data being written out is specified by the setSchema method. If this is not called on the HCatOutputFormat, then by default it is assumed that the the partition has the same schema as the current table level schema Now when I try to omit the schema for HCatInputFormat, it works fine and assumes the default. But when I try to omit the schema for HCatOutputFormat, I get the following error: org.apache.hcatalog.common.HCatException : 9001 : Exception occurred while processing HCat request : It seems that setSchema() is not called on HCatOutputFormat. Please make sure that method is called. >From what I read, it expects that I explicitely define the schema with HCatOutputFormat.setSchema(...), but this is exactly what I would like to omit to assume defaults. This is actually important because it seems that to define the schema, you have to know the order of your table columns in which you specify your List<HCatFieldSchema>, which may not always be obvious. Here is how I create my output table in Hive, which works fine when I'm manipulating it while specifying the schema: hive> create table inventory(word STRING, author STRING, frequency INT) stored as RCFILE; I would like to know if I'm doing something wrong, or if this is simply something not yet implemented in 0.2? Any thoughts would be useful. Thanks, Charles
