I am using spark streaming to write the aggregated output as parquet files to the hdfs using SaveMode.Append. I have an external table created like :
CREATE TABLE if not exists rolluptable
USING org.apache.spark.sql.parquet
OPTIONS (
path "hdfs:////"
);
I had an impression that in case of external table the queries should fetch the data from newly parquet added files also. But, seems like the newly written files are not being picked up.
Dropping and recreating the table every time works fine but not a solution.
Please suggest how can my table have the data from newer files also.
Are you reading those tables with spark?
if so, spark caches parquet tables metadata (since schema discovery can be expensive)
To overcome this, you have 2 options:
Set the config spark.sql.parquet.cacheMetadata to false
refresh the table before the query: sqlContext.refreshTable("my_table")
See here for more details: http://spark.apache.org/docs/latest/sql-programming-guide.html#hive-metastore-parquet-table-conversion
Related
I am trying to understand the spark DataFrame API method called saveAsTable.
I have following question
If I simply write a dataframe using saveAsTable API
df7.write.saveAsTable("t1"), (assuming t1 did not exist earlier), will the newly created table be a hive table which can be read outside spark using Hive QL ?
Does spark also create some non-hive table (which are created using saveAsTable API but can not be read outside spark using HiveQL)?
How can check if a table is Hive Table or Non-Hive table ?
(I am new to big data processing, so pardon me if question is not phrased properly)
Yes. Newly created table will be hive table and can be queried from Hive CLI(Only if the DataFrame is created from single input HDFS path i.e. from non-partitioned single input HDFS path).
Below is the documentation comment in DataFrameWriter.scala class. Documentation link
When the DataFrame is created from a non-partitioned
HadoopFsRelation with a single input path, and the data source
provider can be mapped to an existing Hive builtin SerDe (i.e. ORC and
Parquet), the table is persisted in a Hive compatible format, which
means other systems like Hive will be able to read this table.
Otherwise, the table is persisted in a Spark SQL specific format.
Yes, you can do. You table can be partitioned by a column, but can not use bucketing (its a problem between spark and hive).
I have a simple Hive-External table which is created on top of S3 (Files are in CSV format). When I run the hive query it shows all records and partitions.
However when I use the same table in Spark ( where the Spark SQL has a where condition on the partition column) it does not show that a partition filter is applied. However for a Hive Managed table , Spark is able to use the information of partitions and apply the partition filter.
Is there any flag or setting that can help me make use of partitions of Hive external tables in Spark ? Thanks.
Update :
For some reason, only the spark plan is not showing the Partition Filters. However, when you look at the data loaded its only loading the data needed from the partitions.
Ex: Where rating=0 , loads only one file of 1 MB, when I don't have filter its reads all 3 partition for 3 MB
tl; dr set the following before the running sql for external table
spark.sql("set spark.sql.hive.convertMetastoreOrc=true")
The difference in behaviour is not because of extenal/managed table.
The behaviour depends on two factors
1. Where the table was created(Hive or Spark)
2. File format (I believe it is ORC in this case, from the screen capture)
Where the table was created(Hive or Spark)
If the table was create using Spark APIs, it is considered as Datasource table.
If the table was created usng HiveQL, it is considered as Hive native table.
The metadata of both these tables are store in Hive metastore, the only difference is in the provider field of TBLPROPERTIES of the tables(describe extended <tblName>). The value of the property is orcor empty in Spark table and hive for a Hive.
How spark uses this information
When provider is not hive(datasource table), Spark uses its native way of processing the data.
If provider is hive, Spark uses Hive code to process the data.
Fileformat
Spark gives config flag to instruct the engine to use Datasource way of processing the data for the floowing file formats = Orc and Parquet
Flags:
Orc
val CONVERT_METASTORE_ORC = buildConf("spark.sql.hive.convertMetastoreOrc")
.doc("When set to true, the built-in ORC reader and writer are used to process " +
"ORC tables created by using the HiveQL syntax, instead of Hive serde.")
.booleanConf
.createWithDefault(true)
Parquet
val CONVERT_METASTORE_PARQUET = buildConf("spark.sql.hive.convertMetastoreParquet")
.doc("When set to true, the built-in Parquet reader and writer are used to process " +
"parquet tables created by using the HiveQL syntax, instead of Hive serde.")
.booleanConf
.createWithDefault(true)
I also ran into this kind of problem having multiple joins of internal and external tables.
None of the tricks work including：
spark.sql("set spark.sql.hive.convertMetastoreParquet=false")
spark.sql("set spark.sql.hive.metastorePartitionPruning=true")
spark.sql("set spark.sql.hive.caseSensitiveInferenceMode=NEVER_INFER")
anyone who knows how to solve this problem.
I am having an issue with pyspark sql module. I created a partitioned table and saved it as parquet file into hive table by running spark job after multiple transformations.
Data load is successful into hive and also able to query the data. But when I try to query the same data from spark it says file path doesn't exist.
java.io.FileNotFoundException: File hdfs://localhost:8020/data/path/of/partition partition=15f244ee8f48a2f98539d9d319d49d9c does not exist
The partition which is mentioned in above error was the old partitioned column data which doesn't even exist now.
I have run the spark job which populates a new partition value.
I searched for solutions but all I can see is people say there was no issue in spark version 1.4 and there is an issue in 1.6
Can someone please suggest me the solution for this problem.
I am using Spark 2.2.1 which has a useful option to specify how many records I want to save in each partition of a file; this feature allows to avoid a repartition before writing a file.
However, it seems this option is usable only with the FileWriter interface and not with the DataFrameWriter one:
in this way the option is ignored
df.write.mode("overwrite")
.option("maxRecordsPerFile", 10000)
.insertInto(hive_table)
while in this way it works
df.write.option("maxRecordsPerFile", 10000)
.mode("overwrite").orc(path_hive_table)
so I am directly writing orc files in the HiveMetastore folder of the specified table. The problem is that if I query the Hive table after the insertion, this data is not recognized by Hive.
Do you know if there's a way to write directly partition files inside the hive metastore and make them available also through the Hive table?
Debug steps :
1 . Check the type of file your hive table consumes
Show create table table_name
and check "STORED AS " ..
For better efficiency saves your output in parquet and on the partition location (you can see that in "LOCATION" in above query) ..If there are any other specific types create file as that type.
2 . If you are saving data in any partition and manually creating the partition folder , avoid that .. Create partition using
alter table {table_name} add partition ({partition_column}={value});
3 .After creating the output files in spark .. You can reload those and check for "_corrupt_record" (you can print the dataframe and check this)
Adding to this, I also found out that the command 'MSCK REPAIR TABLE' automatically discovers new partitions inside the hive table folder
I am trying to generate parquet files in S3 file using spark with the goal that presto can be used later to query from parquet. Basically, there is how it looks like,
Kafka-->Spark-->Parquet<--Presto
I am able to generate parquet in S3 using Spark and its working fine. Now, I am looking at presto and what I think I found is that it needs hive meta store to query from parquet. I could not make presto read my parquet files even though parquet saves the schema. So, does it mean at the time of creating the parquet files, the spark job has to also store metadata in hive meta store?
If that is the case, can someone help me find an example of how it's done. To add to the problem, my data schema is changing, so to handle it, I am creating a programmatic schema in spark job and applying it while creating parquet files. And, if I am creating the schema in hive metastore, it needs to be done keeping this in consideration.
Or could you shed light on it if there is any better alternative way?
You keep the Parquet files on S3. Presto's S3 capability is a subcomponent of the Hive connector. As you said, you can let Spark define tables in Spark or you can use Presto for that, e.g.
create table hive.default.xxx (<columns>)
with (format = 'parquet', external_location = 's3://s3-bucket/path/to/table/dir');
(Depending on Hive metastore version and its configuration, you might need to use s3a instead of s3.)
Technically, it should be possible to create a connector that infers tables' schemata from Parquet headers, but I'm not aware of an existing one.