Contents
What is partition pruning in hive?
Partition pruning is a performance optimization that limits the number of files and partitions that Drill reads when querying file systems and Hive tables. The query planner in Drill performs partition pruning by evaluating the filters.
What is key partitioning?
A table partitioning key is an ordered set of one or more columns in a table. The values in the table partitioning key columns are used to determine in which data partition each table row belongs. It is most common to partition data on a date or time column.
What is a partition in a database?
A database partition is a part of a database that consists of its own data, indexes, configuration files, and transaction logs. A partitioned database environment is a database installation that supports the distribution of data across database partitions.
What is strict mode in hive?
Hive Strict Mode ( hive.mapred.mode=strict) enables hive to restrict certain performance intensive operations. Such as – It restricts queries of partitioned tables without a WHERE clause.
What is the default partition when we are loading a hive table in spark?
The default value is 128 MB, see Spark Tuning. With the block size of each block as 128MB. Spark will read the data. Say if your hive table size was aprrox 14.8 GB then it will divide the hive table data into 128 MB blocks and will result in 119 Partitions.
What is Micro partitioning in Snowflake?
All data in Snowflake tables is automatically divided into micro-partitions, which are contiguous units of storage. Each micro-partition contains between 50 MB and 500 MB of uncompressed data (note that the actual size in Snowflake is smaller because data is always stored compressed).
Is partition key primary key?
A composite key is a key formed from multiple columns. A partition key is the primary lookup to find a set of rows, i.e. a partition.
When to use partition pruning in a query?
This “cutting away” of unneeded partitions is known as pruning. When the optimizer can make use of partition pruning in performing this query, execution of the query can be an order of magnitude faster than the same query against a nonpartitioned table containing the same column definitions and data.
How to prune the partitions in the sales table?
The sales table is partitioned by range on the column time_id. One condition in the query is two predicates on time_id, which are combined with an OR operator. This OR predicate is used to prune the partitions in the sales table and a single join between the sales and costs table is performed.
When to use pruning feature in Oracle Database?
Oracle Database pruning feature effectively handles more complex predicates or SQL statements that involve partitioned tables. A common situation is when a partitioned table is joined to the subset of another table, limited by a WHERE condition. For example, consider the following query:
When to use static partition pruning in Oracle?
Oracle determines when to use static pruning primarily based on static predicates. For many cases, Oracle determines the partitions to be accessed at compile time. Static partition pruning occurs if you use static predicates, except for the following cases: Partition pruning occurs using the result of a subquery.