f8015ff68d
Minor compactions can compact several delta directories into a single
delta directory. The current directory filtering algorithm had to be
modified to handle minor compacted directories and prefer those over
plain delta directories. This happens in the Frontend, mostly in
AcidUtils.java.
Hive Streaming Ingestion writes similar delta directories, but they
might contain rows Impala cannot see based on its valid write id list.
E.g. we can have the following delta directory:
full_acid/delta_0000001_0000010/0000 # minWriteId: 1
# maxWriteId: 10
This delta dir contains rows with write ids between 1 and 10. But maybe
we are only allowed to see write ids less than 5. Therefore we need to
check the ACID write id column (named originalTransaction) to determine
which rows are valid.
Delta directories written by Hive Streaming don't have a visibility txn
id, so we can recognize them based on the directory name. If there's
a visibilityTxnId and it is committed => every row is valid:
full_acid/delta_0000001_0000010_v01234 # has visibilityTxnId
# every row is valid
If there's no visibilityTxnId then it was created via Hive Streaming,
therefore we need to validate rows. Fortunately Hive Streaming writes
rows with different write ids into different ORC stripes, therefore we
don't need to validate the write id per row. If we had statistics,
we could validate per stripe, but since Hive Streaming doesn't write
statistics we validate the write id per ORC row batch (an alternative
could be to do a 2-pass read, first we'd read a single value from each
stripe's 'currentTransaction' field, then we'd read the stripe if the
write id is valid).
Testing
* the frontend logic is tested in AcidUtilsTest
* the backend row validation is tested in test_acid_row_validation
Change-Id: I5ed74585a2d73ebbcee763b0545be4412926299d
Reviewed-on: http://gerrit.cloudera.org:8080/15818
Reviewed-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Welcome to Impala
Lightning-fast, distributed SQL queries for petabytes of data stored in Apache Hadoop clusters.
Impala is a modern, massively-distributed, massively-parallel, C++ query engine that lets you analyze, transform and combine data from a variety of data sources:
- Best of breed performance and scalability.
- Support for data stored in HDFS, Apache HBase, Apache Kudu, Amazon S3, Azure Data Lake Storage, Apache Hadoop Ozone and more!
- Wide analytic SQL support, including window functions and subqueries.
- On-the-fly code generation using LLVM to generate lightning-fast code tailored specifically to each individual query.
- Support for the most commonly-used Hadoop file formats, including Apache Parquet and Apache ORC.
- Support for industry-standard security protocols, including Kerberos, LDAP and TLS.
- Apache-licensed, 100% open source.
More about Impala
To learn more about Impala as a business user, or to try Impala live or in a VM, please visit the Impala homepage. Detailed documentation for administrators and users is available at Apache Impala documentation.
If you are interested in contributing to Impala as a developer, or learning more about Impala's internals and architecture, visit the Impala wiki.
Supported Platforms
Impala only supports Linux at the moment.
Export Control Notice
This distribution uses cryptographic software and may be subject to export controls. Please refer to EXPORT_CONTROL.md for more information.
Build Instructions
See Impala's developer documentation to get started.
Detailed build notes has some detailed information on the project layout and build.