What is deferred rebuild in Hive? REBUILD builds an index that was created using the WITH DEFERRED REBUILD clause, or rebuilds a previously built index on the table. You should provide PARTITION details if the table is partitioned.
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How do I create an index in Hadoop Hive?
hive> CREATE INDEX index_students ON TABLE students (id) > AS 'org.apache.hadoop.hive.ql.index.compact.CompactIndexHandler' > WITH DEFERRED REBUILD ; OK Time taken: 0.493 seconds ALTER INDEX … REBUILD builds an index that was created using the WITH DEFERRED REBUILD clause, or rebuilds a previously built index on the table.
Why with deferred rebuild should be present in the created index?
The WITH DEFERRED REBUILD statement should be present in the created index because we need to alter the index in later stages using this statement. This syntax will create an index for our table, but to complete the creation, we need to complete the REBUILD statement. For this to happen, we need to add one more alter statement.
What happens if hive query is executed without index?
For example, let us say you are executing Hive query with filter condition WHERE col1 = 100, without index hive will load entire table or partition to process records and with index on col1 would load part of HDFS file to process records. But be informed that Index on hive table is not recommended.
What is drop Index in hive?
DROP INDEX statement drops the index and delete index table. hive> DROP INDEX IF EXISTS index_students ON students; OK Time taken: 0.27 seconds The improvement in query speed that an index can provide comes at the cost of additional processing to create the index and disk space to store the index references.
Why do we need index in hive?
Can you index a hive table?
What does with deferred rebuild clause in Hive do?
If WITH DEFERRED REBUILD is specified on CREATE INDEX, then the newly created index is initially empty (regardless of whether the table contains any data). The ALTER INDEX ... REBUILD command can be used to build the index structure for all partitions or a single partition.
What is indexing in Hive?
The goal of Hive indexing is to improve the speed of query lookup on certain columns of a table. Without an index, queries with predicates like 'WHERE tab1. col1 = 10' load the entire table or partition and process all the rows.
Why is indexing not preferred in Hive?
Indexes in Hive are not recommended. The reason for this is ORC. ORC has build in Indexes which allow the format to skip blocks of data during read, they also support Bloom filters.
What is compact index in Hive?
Compact indexing stores the pair of indexed column's value and its block id while Bitmap indexing stores the combination of indexed column value and list of rows as a bitmap. Bitmap indexing is a standard technique for indexing columns with few distinct values.
What are the three types of indexing?
Types of indexesUnique indexes enforce the constraint of uniqueness in your index keys.Bidirectional indexes allow for scans in both the forward and reverse directions.Clustered indexes can help improve the performance of queries that traverse the table in key order.More items...
Which file format is best in Hive?
Parquet Files - It is a columnar data format which is suitable for different MapReduce interfaces such as Java, Hive and Pig. It is also ideal for other processing engines such as Impala and Spark. Parquet is good as RC and ORC in performance but slower to write that other column formats.
How do I make Hive run faster?
Types of Performance Tuning Techniques1 Avoid locking of tables. ... 2 Use the Hive execution engine as TEZ. ... 3 Use Hive Cost Based Optimizer (CBO) ... 4 Parallel execution at a Mapper & Reducer level. ... 5 Use STREAMTABLE option. ... 6 Use Map Side JOIN Option. ... 7 Avoid Calculated Fields in JOIN and WHERE clause.More items...•
Which compression is the fastest in Hive?
BZIP2 compression: Bzip2 compresses files more effectively and with a higher compression ratio than Gzip. The compression and decompression are slower than gzip and are more CPU intensive. The generated files have a . bz2 file extension and are splittable.
Can we bucket a Hive table without partitioning?
Bucketing can also be done even without partitioning on Hive tables. Bucketed tables allow much more efficient sampling than the non-bucketed tables.
What is Lpad in Hive?
The LPAD function returns the string with a length of len characters left-padded with pad. Example: LPAD('hive',6,'v') returns 'vvhive' LTRIM( string str ) The LTRIM function removes all the trailing spaces from the string.
What is materialized view in Hive?
Apache Hive works with Apache Calcite to optimize your queries automatically using materialized views you create. Using a materialized view, the optimizer can compare old and new tables, rewrite queries to accelerate processing, and manage maintenance of the materialized view when data updates occur.
Which is faster sparse or dense index?
Dense indices are faster in general, but sparse indices require less space and impose less maintenance for insertions and deletions.
What is the purpose of indexing?
Indexes are used to quickly locate data without having to search every row in a database table every time a database table is accessed. Indexes can be created using one or more columns of a database table, providing the basis for both rapid random lookups and efficient access of ordered records.
What is indexing and why is it used?
Question: Why Indexing is used in database? Answer: An index is a schema object that contains an entry for each value that appears in the indexed column(s) of the table or cluster and provides direct, fast access to rows. Indexes allow the database application to find data fast; without reading the whole table.
What do you mean by indexing?
Indexing, broadly, refers to the use of some benchmark indicator or measure as a reference or yardstick. In finance and economics, indexing is used as a statistical measure for tracking economic data such as inflation, unemployment, gross domestic product (GDP) growth, productivity, and market returns.
What is indexing in Hadoop?
In Distributed file system like HDFS, indexing is diffenent from that of local file system. Here indexing and searching of data is done using the memory of the HDFS node where data is residing. The generated index files are stored in a folder in directory where the actual data is residing.
hadoop - Creating index in hive 0.9 - Stack Overflow
@cybye, I can think of the scenario where partitioning improves query execution dramatically. For example, if the table has add_timestamp, I may partition records according to (year, month, day, etc) then queries that involving select/filter on timestamp would be efficient. However, assume the table has other columns (say location that has no correlation to timestamp) on which I would do ...
sql - Create Hive index on complex column - Stack Overflow
It is possible to create an index on a complex column in hive. Complex as in map, struct, array, etc. columns. Example: CREATE TABLE employees ( name STRING, salary FLOAT, subordinates ARRAY
Indexing in Hive: What is View & Index with Example - Guru99
Hive views are similar to tables, which are generated based on the requirements. Indexes are pointers to particular column name of a table.
Hive - View and Indexes - tutorialspoint.com
Hive - View and Indexes, This chapter describes how to create and manage views. Views are generated based on user requirements. You can save any result set data as a view. The usage of
Hive Indexes - TutorialsCampus
Hive Indexes - Learn Hive in simple and easy steps from basic to advanced concepts with clear examples including Introduction, Architecture, Installation, Data Types, Create Database, Use Database, Alter Database, Drop Database, Tables, Create Table, Alter Table, Load Data to Table, Insert Table, Drop Table, Views, Indexes, Partitioning, Show, Describe, Built-In Operators, Built-In Functions
What is the default value of hive.optimize.index.filter.compact.minsize?
hive.optimize.index.filter.compact.minsize: The default value for this property is 5368709120.
What is the default value of hive.index.compact.query.max.entries?
hive.index.compact.query.max.entries: The default value for this property is 10000000. This property is used to set the maximum number of index entries that use compact indexing during query execution.
Why is index table used in hive?
In Hive, the index table is different than the main table. Indexes facilitate in making query execution or search operation faster. However, storing indexes require disk space and creating an index involves cost. So, the use of indexes may not always be of any benefit.
Why index in hive?
Indexing in Hive helps in case of traversing large data sets and also while building a data model.
What is the purpose of the command "alter index"?
This command ALTER INDEX….REBUILD is used to rebuild an index, which was already built on a table. Partition details should also be provided if the base table has partitions. Indexes need to be rebuilt if the underlying table is overwritten or appended.
When is index deleted?
The index and the indexed table is deleted automatically if the table on which index was built is dropped. Similarly, if a partitioned table is indexed then on dropping the partitions, the indexes are also automatically deleted.
Does indexing in hive always benefit?
So, the use of indexes may not always be of any benefit. “EXPLAIN” query must be checked to evaluate the benefit through a query execution plan. Indexing in hive makes large dataset analysis relatively quicker by better query performance on operations.
Why do we need index in hive?
The main goal of creating INDEX on Hive table is to improve the data retrieval speed and optimize query performance. For example, let us say you are executing Hive query with filter condition WHERE col1 = 100, without index hive will load entire table or partition to process records and with index on col1 would load part of HDFS file to process records.
Can you index a hive table?
But be informed that Index on hive table is not recommended. The create index will help if you are migrating your existing data warehouse to Hive and you have transformed the query with index as it is.