I am trying to alter my cassandra tables starting with a specific name.
My table starts with sample_1,sample_2,sample_13567,sample_adgf and so on...
The table names are random but starting with same prefix.
I want to add a new column to all these tables.
Can some one suggest me the update query using the regex for table names.
If you are using linux You can this in two step :
First Generate all alter command into a file like below :
for i in {1..13567}; do echo "ALTER TABLE sample_$i ADD test text;"; done > alter.cql
The above command will create alter command to add test text column for table sample_1 to sample_13567 and store into a file alter.cql
Now you can just load the cql file into cqlsh like below :
cqlsh 127.0.0.1 -u cassandra -p cassandra -k ashraful_test -f alter.cql
Here
-u username
-p password
-k keyspace_name
-f file name to load
By the way having too much table is not a good idea.
Check this link https://stackoverflow.com/a/33389204/2320144
Related
I'm trying to use mysqldump to backup my databases - data and all. I can use this command to dump the data on the command line:
mysqldump -u username -ppassword --skip-lock-tables --databases database
That works great, and I have a full mass insert statement with all the data. if I do this however:
mysqldump -u username -ppassword --skip-lock-tables --databases database > /var/backup/$(date +\%d-\%m-\%Y)_dump.sql
to add the output to a file (I've checked that the file name scheme works), I only get the create and update commands, and one row of data for each table. I've also tried this without --skip-lock-tables, but I wanted to make sure this wasn't a problem with getting a lock. This will eventually go into a cron job, so I'd like to be able to keep this to one line if possible.
The output on the command line is quite long, but here is an example of part of the mass insert statement:
/*!40000 ALTER TABLE `clients` DISABLE KEYS */;
INSERT INTO `clients` VALUES (1,'nicholas','sallis','it#konditormeister.com','11 hunnewell circle ','newton','02458','ma','7818491970','2016-05-10 16:17:55','2016-05-10 16:17:55')
I have a Cassandra 2.1.8 database with a bunch of tables, all in the form of either "prefix1_tablename" or "prefix2_tablename".
I want to DROP every table that begins with prefix1_ and leave anything else alone.
I know I can grab table names using the query:
SELECT columnfamily_name FROM system.schema_columnfamilies
WHERE keyspace_name='mykeyspace'
And I thought about filtering the results somehow to get only prefix1_ tables, putting them into a table with DROP TABLE prepended to each one, then executing all the statements in my new table. It was similar thinking to strategies I've seen for people solving the same problem with MySQL or Oracle.
With CQL3.2 though, I don't have access to User-Defined Functions (at least according to the docs I've read...) and I don't know how to do something like execute statements off of a table query result, as well as even how to filter out prefix1_ tables with no LIKE operator in Cassandra.
Is there a way to accomplish this?
I came up with a Bash shell script to solve my own issue. Once I realized that I could export the column families table to a CSV file, it made more sense to me to perform the filtering and text manipulation with grep and awk as opposed to finding a 'pure' cqlsh method.
The script I used:
#!/bin/bash
# No need for a USE command by making delimiter a period
cqlsh -e "COPY system.schema_columnfamilies (keyspace_name, columnfamily_name)
TO 'alltables.csv' WITH DELIMITER = '.';"
cat alltables.csv | grep -e '^mykeyspace.prefix1_' \
| awk '{print "DROP TABLE " $0 ";"}' >> remove_prefix1.cql
cqlsh -f 'remove_prefix1.cql'
rm alltables.csv remove_prefix1.cql
I am trying to export data from cassandra using CQL client. A column family has about 100000 rows in it. when i am copying dta into csv file using COPY TO command i get following rpc_time out error.
copy mycolfamily to '/root/mycolfamily.csv'
Request did not complete within rpc_timeout.
I am running in:
[cqlsh 3.1.6 | Cassandra 1.2.8 | CQL spec 3.0.0 | Thrift protocol 19.36.0]
How can I increase RPC timeout limit?
I tried adding rpc_timeout_in_ms: 20000 (defalut is 10000) in my conf/cassandra.yaml file. but while restarting cassandra I get:
[root#user ~]# null; Can't construct a java object for tag:yaml.org,2002:org.apache.cassandra.config.Config; exception=Cannot create property=rpc_timeout_in_ms for JavaBean=org.apache.cassandra.config.Config#71bfc4fc; Unable to find property 'rpc_timeout_in_ms' on class: org.apache.cassandra.config.Config
Invalid yaml; unable to start server. See log for stacktrace.
The COPY command currently does the same thing with SELECT with LIMIT 99999999. So, it will eventually goes to timeout while your data is growing. Here's the export function;
https://github.com/apache/cassandra/blob/trunk/bin/cqlsh#L1524
I'm doing the same export on production. What I'm doing is the following;
make select * from table where timeuuid = someTimeuuid limit 10000
write the result set to a csv file w/ >> mode
make the next selects with respect to the last timeuuid
You can pipe command in cqlsh by the following cqlsh command
echo "{$cql}" | /usr/bin/cqlsh -u user -p password localhost 9160 > file.csv
You can use Auto pagination by specifying fetch size in Datastax Java driver.
Statement stmt = new SimpleStatement("SELECT id FROM mycolfamily;");
stmt.setFetchSize(500);
session.execute(stmt);
for (Row r:result.all()){
//write to file
}
I have encountered the same problem a few minutes ago then I have found CAPTURE and it worked:
First start capturing on cqlsh and then run your query with some limiting of your choice.
http://www.datastax.com/documentation/cql/3.0/cql/cql_reference/capture_r.html
The best way yo export the data is using nodetool snapshot option. This returns immediately and can be restored later on. The only issue is that this export is per node and for the entire cluster.
Example:
nodetool -h localhost -p 7199 snapshot
See reference:
http://docs.datastax.com/en/archived/cassandra/1.1/docs/backup_restore.html#taking-a-snapshot
I want to copy selected rows from a columnfamily to a .csv file. The copy command is available just to dump a column or entire table to a file without where clause. Is there a way to use where clause in copy command?
Another way I thought of was,
Do "Insert into table2 () values ( select * from table1 where <where_clause>);" and then dump the table2 to .csv , which is also not possible.
Any help would be much appreciated.
There are no way to make a where clause in copy, but you can use this method :
echo "select c1,c2.... FROM keySpace.Table where ;" | bin/cqlsh > output.csv
It allows you to save your result in the output.csv file.
No, there is no built-in support for a "where" clause when exporting to a CSV file.
One alternative would be to write your own script using one of the drivers. In the script you would do the "select", then read the results and write out to a CSV file.
In addition to Amine CHERIFI's answer:
| sed -e 's/^\s+//; s_\s*\|\s*_,_g; /^-{3,}|^$|^\(.+\)$/d'
Removes spaces
Replaces | with ,
Removes header separator, empty and summary lines
Other ways to run the SQL with filter and redirect the response to csv
1) Inside the cqlsh, use the CAPTURE command and redirect the output to a file. You need to set the tracing on before executing the command
Example: CAPTURE 'output.txt' -- output of the sql executed after this command gets captured into output.txt file
2) In case if you would like to redirect the SQL output to a file from outside of cqlsh
./cqlsh -e'select * from keyspaceName.tableName' > fileName.txt -- hostname
I'm looking for a way to delete all of the rows from a given column family in cassandra.
This is the equivalent of TRUNCATE TABLE in SQL.
You can use the truncate thrift call, or the TRUNCATE <table> command in CQL.
http://www.datastax.com/docs/1.0/references/cql/TRUNCATE
You can also do this via Cassandra CQL.
$ cqlsh
Connected to Test Cluster at localhost:9160.
[cqlsh 4.1.1 | Cassandra 2.0.6 | CQL spec 3.1.1 | Thrift protocol 19.39.0]
Use HELP for help.
cqlsh> TRUNCATE my_keyspace.my_column_family;
Its very simple in Astyanax. Just a Single Line statement
/* keyspace variable is Keyspace Type */
keyspace.truncateColumnFamily(ColumnFamilyName);
If you are using Hector it is easy as well:
cluster.truncate("our keyspace name here", "your column family name here");
If you are using cqlsh, then you can either do it in 2 ways
use keyspace; and then truncate column_family;
truncate keyspace.column_family;
If you want to use DataStax Java driver, you can look at -
http://www.datastax.com/drivers/java/1.0/com/datastax/driver/core/querybuilder/QueryBuilder.html
or
http://www.datastax.com/drivers/java/2.0/com/datastax/driver/core/querybuilder/Truncate.html
depending on your version.
if you are working on cluster setup, truncate can only be used when all the nodes of the cluster are UP.
By using truncate, we will miss the data(we are not sure with the importance of the data)
So the very safe way as well a trick to delete data is to use COPY command,
1) backup data using copy cassandra cmd
copy tablename to 'path'
2) duplicate the file using linux cp cmd
cp 'src path' 'dst path'
3) edit duplicate file in dst path, delete all lines expect first line.
save the file.
4) use copy cassandra cmd to import
copy tablename from 'dst path'