Creating Column Families

About this task

There are several methods that you can use to create column families in MapR-DB tables. To create column families, you must have the following permissions:

  • readAce and writeAce on the volume
  • lookupdir on directories in the path to the table
  • createrenamefamilyperm on the table

Creating Column Families Using MCS

About this task

To create a column family from MCS, under Data > Tables:

Procedure

  1. Click:
    • Take me to Add Column Family after creating a new table.
    • Add Column Family in the Column Families tab in the table information page.

      See Viewing Table Information.

  2. Specify the following properties to set up column families.
    Column Family Name The name of the column family.
    JSON Path The path to the column family in dotted notation. For example, suppose the table contained JSON documents that were of this general structure: 
    {
     "_id" : "ID",
     "a" :
          {
               "b" : 
                    {
                         "c" : "value",
                    },
               "e" : "value"
          }
}
    If you want to create a column family at the field d nested within b, your new path would be a.b.d.
    NOTE: Ensure that the field at which you want to create the column family does not yet exist. If the field exists, it could become inaccessible after the column family is created.
    Compression The compression setting to use for the column family. Valid options are off, lzf, lz4, and zlib. The default setting is the same as the compression setting for the directory where the table is located. To find out whether a directory is compressed and the type of compression, see Turning Compression On or Off on Directories Using the CLI.
    Time-to-Live Specifies whether to purge data when the age of the data in this column family exceeds the value specified here. Data can remain forever or can be purged after specified amount of time (in seconds). Setting the value to 0 is equivalent to allowing data to remain indefinitely or forever.
    NOTE: If the value for an existing column family in a JSON table is not 0, you cannot add another column family.
    In Memory Determines whether preference is given to values of this column family for storage with row keys. Because row keys are cached in memory in preference to row data, column-family data that is stored inline with the row keys is also cached in memory.

    For all column families in a table together, up to 200 bytes of row data will be stored inline with each row key. Storing data inline with a row key might speed retrieval of the data from a column family because disk access can often be avoided. For each column family, up to 32 bytes can be stored inline with each row key even if this is disabled (No), but preference will be given to column families where this is enabled (Yes). A column family can have more than 32 bytes stored inline if this is enabled.

    If the total number of bytes for all column families together exceeds 200 for a row, then preference for inclusion within the inline storage for that row is given to column families that have this enabled.

    NOTE: All of the data for a column family will be stored in-line with the row key, or none will be. If the contents in a column family for a particular row are larger than the maximum number of bytes that are allowed to be stored for that column family, no data will be stored in-line for that column family.
    By default, this is enabled.
    Column Family Name The name of the column family.
    Version
    • Minimum — The minimum number of versions of column values to keep. The default is zero.
    • Maximum — Maximum number of versions of column values to keep. The default is one.
    Compression The compression setting to use for the column family. Valid options are off, lzf, lz4, and zlib. The default setting is the same as the compression setting for the directory where the table is located. To find out whether a directory is compressed and the type of compression, see Turning Compression On or Off on Directories Using the CLI.
    Time-to-Live Specifies whether to purge data when the age of the data in this column family exceeds the value specified here. Data can remain forever or can be purged after specified amount of time (in seconds). Setting the value to 0 is equivalent to allowing data to remain indefinitely or forever.
    In Memory Determines whether preference is given to values of this column family for storage with row keys. Because row keys are cached in memory in preference to row data, column-family data that is stored inline with the row keys is also cached in memory.

    For all column families in a table together, up to 200 bytes of row data will be stored inline with each row key. Storing data inline with a row key might speed retrieval of the data from a column family because disk access can often be avoided. For each column family, up to 32 bytes can be stored inline with each row key even if this is disabled (No), but preference will be given to column families where this is enabled (Yes). A column family can have more than 32 bytes stored inline if this is enabled.

    If the total number of bytes for all column families together exceeds 200 for a row, then preference for inclusion within the inline storage for that row is given to column families that have this enabled.

    NOTE: All of the data for a column family will be stored in-line with the row key, or none will be. If the contents in a column family for a particular row are larger than the maximum number of bytes that are allowed to be stored for that column family, no data will be stored in-line for that column family.
    By default, this is enabled.
  3. Set up access to column families for users, groups, and/or roles.
    You can use either the default permissions or proceed to define new permissions for this column family.
    Read Data Can do column reads. Reads require permission both at the column-family level and at the field level. This permission is inherited by fields within the column family.
    Write Data Can do column writes. Writes require permission both at the column-family level and at the field level. This permission is inherited by fields within the column family.
    Traverse Data Can pass over fields in JSON documents. For example, suppose that a JSON table contains documents of this general structure:
    {
     "_id" : "ID",
     "a" :
          {
               "b" : "value",
               "c" : "value"
          }
}
    Suppose further that the user sjohnson has read permission on a.b, but not on a. For sjohnson to read a.b, the user needs the traverse permission on a. The user can then pass over field a to a.b. This permission is inherited by fields within the column family.
    Set Version Can set or change the maximum and minimum number of versions of column values to keep.
    Set Compression Can set or change the compression setting for the column family.
    Read Data Can do column reads. Reads require permission both at the column-family level and at the field level. This permission is inherited by fields within the column family.
    Write Data Can do column writes. Writes require permission both at the column-family level and at the field level. This permission is inherited by fields within the column family.
    Append Data Can do column appends. Column appends require permission both at the column-family level and at the column level.
    Set Version Can set or change the maximum and minimum number of versions of column values to keep.
    Set Compression Can set or change the compression setting for the column family.
    By default, all permissions are given to the user creating the table.
    To grant or block access to users, groups, and/or roles, from the:
    • Basic settings, select the type — public, (OR) user, group, or role — from the drop-down menu, specify the name of the user, group, or role, and select one or more checkbox to grant permissions.
      TIP: Click to create a copy of the associated access control setting. Click to remove the associated access control expression.
      To add access control expressions for another user, group, or role, click Add Another and repeat this step.
    • Advanced settings, or specify public (p) or user (u), group (g), and/or role (r) who have and/or do not have the type of access using the following boolean expressions and subexpressions:
      • ! — Negation operator.
      • & — AND operation.
      • | — OR operation.
      Use (), parentheses, for subexpressions.
      NOTE: You cannot specify user, group, or role individually if access is granted to all users (public).

      Alternatively, click associated with the type of access to use the Access Control Expression window to define access for public or users, group, and/or role. See Defining ACEs for more information.

    NOTE: If you switch from Basic to Advanced, the basic settings, if any, will be carried over to the advanced settings. If you switch from Advanced to Basic, all the settings will be lost because the subexpressions and AND (&) and negation (!) operations that are supported by advanced settings are not supported in the basic settings.
  4. Specify:
    Field Permissions (for JSON Tables)
    Specify a name for the field and the permissions to access the field. By default, a field inherits permissions from the column in which the field is located. Permissions set at this level override permissions inherited from the column. You can set the following permissions by selecting the associated checkbox:
    Read Data Can read from the field. This permission extends to fields that are nested below as well unless explicitly denied on any of the nested fields.
    Write Data Can delete the field, insert a value into the field, or overwrite the field's value.
    NOTE: Deleting a field also deletes all fields that are nested within that field, even those fields on which the write permission is explicitly denied.
    JSON Traverse Can descend a hierarchy of fields to access the fields to read or write.
    By default, all permissions are given to the user creating the table. See Permission Types for Fields and Column Families in JSON Tables for more information.
    Column Permission (for Binary Tables)
    Create (by clicking Add Column and specifying a name in the Column Name field) and set permissions for columns in the column family. You can set the following permissions by selecting the associated checkbox:
    Read Data Can do column reads. Reads require permission both at the column-family level and at the field level. This permission is inherited by fields within the column family.
    Write Data Can do column writes. Writes require permission both at the column-family level and at the field level. This permission is inherited by fields within the column family.
    Append Data Can do column appends. Column appends require permission both at the column-family level and at the column level.
    NOTE: When a user, group, or role requests to read data from, write data to, or append data to a column, MapR-DB checks whether that user, group, or role has read or write permission for the column family AND read or write permission for the column. By default, columns allow read and write access to all users; in such cases, only the read or write permission for the column family matters.

    However, suppose that a table contains columns col1 and col2 in column family cf1, and these columns grant read and write permission only to the table creator. A different user tries to write data to these columns. MapR-DB checks whether this user has write permission on cf1 AND col1 AND col2. If the user does not have all three permissions, MapR-DB returns an error that says access for the write is denied.

    If this user were to try to read from the same two columns, MapR-DB would simply not return the data. If the user tried to read from those two columns and additional columns on which the user had read permissions, the results would contain the data for those additional columns, but exclude the data for col1 and col2.

    You can add columns to a table at any time. Null columns for a given row don't take up any storage space.
    NOTE: Extremely wide tables with very large numbers of columns can sometimes reach the recommended size for a table split at a comparatively small number of rows because MapR-DB tables split at the row level, not the column level.
    To grant or block access to users, groups, and/or roles, from the:
    • Basic settings, select the type — public, (OR) user, group, or role — from the drop-down menu, specify the name of the user, group, or role, and select one or more checkbox to grant permissions.
      TIP: Click to create a copy of the associated access control setting. Click to remove the associated access control expression.
      To add access control expressions for another user, group, or role, click Add Another and repeat this step.
    • Advanced settings, or specify public (p) or user (u), group (g), and/or role (r) who have and/or do not have the type of access using the following boolean expressions and subexpressions:
      • ! — Negation operator.
      • & — AND operation.
      • | — OR operation.
      Use (), parentheses, for subexpressions.
      NOTE: You cannot specify user, group, or role individually if access is granted to all users (public).

      Alternatively, click associated with the type of access to use the Access Control Expression window to define access for public or users, group, and/or role. See Defining ACEs for more information.

    NOTE: If you switch from Basic to Advanced, the basic settings, if any, will be carried over to the advanced settings. If you switch from Advanced to Basic, all the settings will be lost because the subexpressions and AND (&) and negation (!) operations that are supported by advanced settings are not supported in the basic settings.
  5. Click Add Column Family to add the column family to the table.

Creating Column Families Using CLI or the REST API

About this task

To create a column family in a JSON table, include the parameters -jsonpath and -force :
maprcli table cf create -path <path> -cfname <name_of_column_family> -jsonpath 
                                <path> -force true
For the full list of options for this command, see table cf create.
The -jsonpath parameter specifies the path to the column family. The path is in dotted notation. For example, suppose the table contained JSON documents that were of this general structure: 
{
     "_id" : "ID",
     "a" :
          {
               "b" : 
                    {
                         "c" : "value",
                    },
               "e" : "value"
          }
}
You want to create a column family at the field d in the new path a.b.d because you plan to store image files in fields in that column family.
IMPORTANT: Ensure that the field at which you want to create the column family does not yet exist. Also ensure that there are no secondary indexes defined on the field. If the field does exist or is a field in an index, the data in the field could become inaccessible after you create the column family.

By default, every time you try to create a non-default column family in a JSON table, this command fails and returns a warning message that you should ensure there is no existing data at the specified path. Set the -force parameter to true if you want to override this warning mechanism and create a column family.

The command to create a column family for a binary table is:
maprcli table cf create -path <path> -cfname <name_of_column_family>
For the full list of options for this command, see table cf create.

The format of the value of the -path parameter depends on whether you are creating a table on a local cluster or a remote cluster.

Creating a Column Family for a Binary Table Using HBase Shell

About this task

After starting the HBase shell, run the alter command. Type help to see a list of commands and their syntax.