aws glue tables created by athena are read twice by emr spark - amazon-web-services

When I create a table in athena with CTAS syntax (example below), tables are registered to glue in a way that when I read the same table on an EMR cluster with (py)spark, every partition is read twice, but when I read it with athena, it is alright. When I create a table through spark with write.saveAsTable syntax, it's registered to glue properly and this table is read properly with spark and with athena.
I didn't find anything in the spark/athena/glue documentation about this. After some trial and errors I found out that there is a glue table property that is set by spark and not set by athena: spark.sql.sources.provider='parquet'. When I set this manually on tables created via athena, spark will read it properly. But this feels like an ugly workaround and I would like to understand what's happening in the background. And I didn't find anything about this table property.
Athena create table syntax:
CREATE TABLE {database}.{table}
WITH (format = 'Parquet',
parquet_compression = 'SNAPPY',
external_location = '{s3path}')
AS SELECT

Related

Populate external schema table in Redshift from S3 bucket file

I am new to AWS and trying to figure out how to populate a table within an external schema, residing in Amazon Redshift. I used Amazon Glue to create a table from a .csv file that sits in a S3 bucket. I can query the newly created table via Amazon Athena.
Here is where I am stuck because my task is to take the data and populate a table living in an RedShift external schema. I tried created a Job within Glue, but had no luck.
This is where I am stuck. Am I supposed to first create an empty destination table that mirrors the table that I can query using Athena?
Thank you to anyone in advance who might be able to assist!!!
Redshift Spectrum and Athena both use the Glue data catalog for external tables. When you create a new Redshift external schema that points at your existing Glue catalog the tables it contains will immediately exist in Redshift.
-- Create the Redshift Spectrum schema
CREATE EXTERNAL SCHEMA IF NOT EXISTS my_redshift_schema
FROM DATA CATALOG DATABASE 'my_glue_database'
IAM_ROLE 'arn:aws:iam:::role/MyIAMRole'
;
-- Review the schema info
SELECT *
FROM svv_external_schemas
WHERE schemaname = 'my_redshift_schema'
;
-- Review the tables in the schema
SELECT *
FROM svv_external_tables
WHERE schemaname = 'my_redshift_schema'
;
-- Confirm that the table returns data
SELECT *
FROM my_redshift_schema.my_external_table LIMIT 10
;

While Running AWS Athena query Query says Zero Records Returned

SELECT * FROM "sampledb"."parquetcheck" limit 10;
Trying to use Parquet file in S3 and created a table in AWS Athena and it is created perfectly.
However when I run the select query, it says "Zero Records Returned."
Although My Parquet file in S3 has data.
I have created partition too. IAM has full access on Athena.
If your specified columns names are correct, then you may need to load the partitions using: MSCK REPAIR TABLE EnterYourTableName;. This will add new partitions to the Glue Catalog.
If any of the above fails, you can create a temporary Glue Crawler to crawl your table and then validate the metadata in Athena by clicking the 3 dots next to the table name. Then select Generate Create Table DDL. You can then compare any differences in DDL.

HIVE_UNKNOWN_ERROR when running AWS Athena query on Glue table (RDS)

I'm getting an error when running an Athena query against a Glue table created from an RDS database:
HIVE_UNKNOWN_ERROR: Unable to create input format
The tables are created using a crawler. The tables show up correctly in the Glue interface:
However, they do not show up in the Athena interface under the database. It says: "The selected database has no tables"
I do not see this behaviour when using a database created using an S3 file. Maybe this is related to the error. Does anybody have an idea?
I had the same problem. This is the answer that I have got from AWS Support:
I understand that you set up a Glue crawler to crawl our RDS postresql database but the tables are not visible in Athena.
Athena service is designed to query tables that point to S3 as data-source. It cannot read data from non-S3 resources as of today.
So, unfortunately not possible at the moment.

AWS Glue Crawler overwrite custom table properties

I have a data catalog managed by AWS Glue, and any update that my developers does in our S3 bucket with new tables or partitions we are using the crawlers to update that every day to keep the new partitions healthy.
But, we also need custom table properties. In our hive we have the data source of each table as a table property, and we added to the tables in the Data Catalog in glue but, every time we run the crawler it overwrites the custom table properties like Description.
Am I doing anything wrong? Or is this a bug from AWS Glue?
Have you checked Schema change policy in your crawler definition?

Exporting Spark Dataframe to Athena

I'm running a pyspark job which creates a dataframe and stores it to S3 as below:
df.write.saveAsTable(table_name, format="orc", mode="overwrite", path=s3_path)
I can read the orcfile without a problem, just by using spark.read.orc(s3_path), so there's schema information in the orcfile, as expected.
However, I'd really like to view the dataframe contents using Athena. Clearly if I wrote to my hive metastore, I can call hive and do a show create table ${table_name}, but that's a lot of work when all I want is a simple schema.
Is there another way?
One of the approaches would be to set up a Glue crawler for your S3 path, which would create a table in the AWS Glue Data Catalog. Alternatively, you could create the Glue table definition via the Glue API.
The AWS Glue Data Catalog is fully integrated with Athena, so you would see your Glue table in Athena, and be able to query it directly:
http://docs.aws.amazon.com/athena/latest/ug/glue-athena.html