of each mapper task for associated operations. called a map Association.
The mapreduce used to execute the job is only mapper and has no reducer. So in a right or full outer type of association, this does not work, because in these cases it is only possible to determine if there is really no matching record until all the inputs are aggregated at the reducer stage. In the left association of the figure below, we can see from the log that reducer is not enabled:
In full join, a reducer is enable
hive.optimize.cp=true: Column clipping, fetching onlywhen reading the data, only the columns that are needed in the query are read, and the other columns are ignored. For example, for a query: SELECT A, b from T Wheree Hive.optimize.prunner: Partition croppingLIMIThive.limit.optimize.enable=true: Optimizing the Limit N statementwhen using the simple limit sampling data when the
1. First set the small file standard in the hive-site.xml. lt; propertygt; lt; namegt; hive. merge. smallfiles. avgsizelt; namegt; lt; va
1. First set the small file standard in the hive-site.xml. lt; propertygt; lt; namegt; hive. merge. smallfiles. avgsizelt;/namegt; lt; va
Homepage → Database Technology
Hive optimization Summary
--- By Hualien
Hive SQLAs map reduceThere will be unexpected surprises.
Understanding hadoopHiveThe foundation of optimization. This is a summary of the valuable experience of all members of the project team over the past year.
Long-term Observation of hadoop's data processing process has
Transferred from: http://www.aboutyun.com/forum.php?mod=viewthreadtid=8590highlight=hive
Questions Guide:1. How to view the hive table structure.2. How to view table structure information.3. How to view the partition information.4. Which command can blur the search table
1.hive Fuzzy Search Table
Show tables like ' *name* ';
2. View table structure Information
query to see how many MR jobs hive will use for a query: " This section is detailed later "Hive> explain >Select Sales. *, things. * > from Join on (Sales.id=things.id);2. External connectionAn outer join allows you to find rows of data that cannot be matched in the join table .In front of the inner connecti
Hive SQL optimization: distribute by, sort by, and hivedistributeHiveSQL has been optimized recently,
The following is an SQL statement that sorts records from the first row of each group after grouping.
INSERTOVERWRITETABLET_wa_funnel_distinct_tempPARTITION(Pt = '$ {SRCTIME }')
SELECT
Bussiness_id,
Cookie_id,
Session_id,
Funnel_id,
Group_first (funnel_name)Funnel_name,
Step_id,
Group_first (step_
Recently in the design and development of a generic query restful Service (https://github.com/lalaguozhe/polestar-1), project name Polestar (Chinese name Polaris, camping lights, instructors, Hope that everyone's query to attract convergence, you know, before the query hive statements are basically walking
I. Job input and output optimizationUse Muti-insert, union All, the union all of the different tables equals multiple inputs, union all of the same table, quite map outputExample Second, data tailoring2.1. Column ClippingWhen hive reads the data, it can query only the columns that are needed, ignoring the other columns. You can even use an expression that is being expressed.See. Http://www.cnblogs.com/bjlh
Small files automatically merged and output based on Hive Optimization
1. First set the small file standard in the hive-site.xml.
2. Only map mapreduce output and merge small files.
3. Output mapreduce with reduce and merge small files.
Hive programming guide PDF (Chinese Version)
Hadoop cluster-based
Hive and HBase integration, query exception, re-execute the Hive statistical command, there may be exceptions, because my MapReduce has been used before, and has already added pro to Hadoop
Hive and HBase integration, query exception, re-execute the
A new feature has been introduced in the Hive0.11.0 version that allows users to specify the delimiter for a column when the user outputs the hive query results to a file, whereas the previous version is not a separator between columns.Before Hive0.11.0 the version is used as follows, cannot specify delimiter, default is \x01:Hive (
time for member transactionsSelect A.id,t.dt from Hive_dt t join (select ID, min (dt) Min_dt from Hive_mapjoin Group by ID) awhere t.dt>= A.min_dt) fLeft outer joins Hive_mapjoin k on f.dt = K.dt and f.id = k.id;--With MapjoinCREATE TABLE Hive_ok_mapjoin as select F.id,f.dt, Coalesce (k.amt,0.0) Amt from (--to ask Members to have a continuous time since the transactionJoin (--Minimum time for member transactionsLeft outer join tmp.tst1 kon F.dt = k.dt and f.id = k.id;Test result: No Mapjoin exe
Tags: hive join1. Small and large table joinWhen small tables and large tables are joinedSmall tables placed on the front sideHive caches small tables.2. mapjoinUse mapjoin to put small tables into the memory and match the large tables one by one on the map side to save the reduce workload.Example:Select/* + mapjoin (B) */a. A1, A. A2, B. B2 from tablea a join tableb B on A. A1 = B. B1After version 0.7, you can also use the configuration to automatica
Optimization of the Hive's IaaS Cloud host Quick Start?? Use of Linux, do not use the desktop Technology (NO) (limited) Large (installed) take (X) cheese probably have experience, the computer's operating start time is very fast, often in a few seconds level of completion. But in the same non-desktop cloud host boot often give us is not such a feeling, especially in the first creation process, always found that the boot process needs to 10s+ time, so
Recently, when using hive, You need to export the data queried by hive to the local file system. The hql syntax is as follows:
Insert overwrite [local] Directory directory1 select_statement1 after the query result is exported to a local file, it is difficult to use Excel to load the file: do not know the delimiter used when the
Hive only supports the use of subqueries in the FROM clause, the subquery must have a name, and the column must be unique: SELECT ... From (subquery) name ... Confirm that the column must be unique under certain requirements. To build a table statement:
CREATE TABLE Tb_in_base (id bigint, devid bigint, devname string
) partitioned by (job_time bigint) row format delimited fields terminated by ', ';
CREATE TABLE tb_in_up (id bigint, devid bigint, dev
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