metadata synchronization issues among impala
impala among database tables created, you could see directly, without having to refresh
the database tables hive which created the need to refresh the metadata to be able to see
Because the catalog service impala, we need to refresh mechanism, metadata hive of information among the tables, save to catalog come inside, to be able to see impala
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9, impala use
9.1, impala-shell syntax
9.1.1 External impala-shell command parameter syntax
You do not need to enter the command parameter impala-shell interactive command line which can be executed
impala-shell when executed later can take a number of parameters:
-h help documentation
impala-shell -h
-r to refresh the entire metadata, when a large amount of data, more consumption of server performance
impala-shell -r
-B to format, query large amounts of data can improve performance
--print_header to format the display column name
--output_delimiter specify the delimiter
-v view the corresponding version
impala-shell -v -V
-f execute the query file
--query_file specify the query file
cd /export/servers
vim impala-shell.sql
use weblog;
select * from ods_click_pageviews limit 10;
To execute the query by -f parameter file
impala-shell -f impala-shell.sql
-i connected to impalad
--impalad designated impalad to perform the task
-o save the results to a file which go
--output_file specify the output file name
impala-shell -f impala-shell.sql -o hello.txt
-p Displays the query plan
impala-shell -f impala-shell.sql -p
-q Do not use impala-shell query
9.1.2, impala-shell internal command line parameter syntax
After entering the syntax impala-shell command line can be executed
help command
Help documentation
connect command
connect hostname to connect to a machine to perform the above
refresh command
refresh dbname.tablename incremental refresh, a refresh of a metadata table, mainly for refreshing data of the data table changes inside the hive which case
refresh mydb.stu;
invalidate metadata 命令：
invalidate metadata refresh the whole amount, a large consumption performance, which is mainly used in the new hive database or database tables when refresh is performed
explain the command:
For viewing sql statement execution plan
explain select * from stu;
Explain value may be set to several values 0,1,2,3 the like, where the level 3 is the highest, can print out the most complete information
set explain_level=3;
profile command:
After executing sql statement execution, you can print a more detailed implementation steps,
Mainly used to query results view, excellent tone clusters
select * from stu;
profile;
Note: insert in the hive window which data or new database or database tables, in impala which is not a query directly to the need to refresh the database, inserted in impala-shell which data, in impala which can query directly to, do not need to refresh the database, which is the catalog to use this feature service implementation, catalog is added after impala1.2 version of the module functions, the main role is to synchronize metadata between impala