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https://issues.apache.org/jira/browse/HBASE-24901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17180815#comment-17180815
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Elliot Miller commented on HBASE-24901:
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{quote}Lovely. What determines the widths? Is it on by default? Does the width
size to the terminal? Does it handle binaries? What happens when value is 100MB?
{quote}
Any command has the power to specify which columns have a fixed width. For
example, most commands will fix the width of the {{timestamp}} column since
ISO8601 timestamps are always the same width (when in UTC with millisecond
precision). The AlignedTableFormatter is the only implementation of
TableFormatter that cares about column widths. It calculates adds up all the
reserved space and subtracts that from the terminal width to determine how much
free space it has. It evenly divides the free space among any columns that do
not have a fixed width.
When the AlignedTableFormatter is used non-interactively, it uses a reasonable
arbitrary width for the table, which I set to be 100 characters wide.
> Create versatile hbase-shell table formatter
> --------------------------------------------
>
> Key: HBASE-24901
> URL: https://issues.apache.org/jira/browse/HBASE-24901
> Project: HBase
> Issue Type: Improvement
> Components: shell
> Affects Versions: 3.0.0-alpha-1
> Reporter: Elliot Miller
> Assignee: Elliot Miller
> Priority: Major
> Attachments: HBASE-24901_scan_output_comparison.png
>
>
> As a user, I would like a simple interface for shell output that can be
> expressed as a table (ie. output with a fixed number of columns and
> potentially many rows). To be clear, this new formatter is not specifically
> for HBase "tables." Table is used in the broader sense here.
> h2. Goals
> - Do not require more than one output cell loaded in memory at a time
> - Support many implementations like aligned human-friendly tables, unaligned
> delimited, and JSON
> h2. Non-goals
> - Don't load all the headers into memory at once.
> ** This may seem like a goal with merit, but we are unlikely to find a use
> case for this formatter with many columns. For example: since HBase tables
> aren't relational, our scan output will not have an output column for every
> HBase column. Instead, each output row will correspond to an HBase cell.
> ** It's also really useful to have the headers ahead of time, because it
> allows us to do things like JSON object output (where each row is represented
> with key-value pairs).
> h2. Implementation
> This patch was implemented as a stateful output formatter for data with a
> fixed number of output columns. Tracking state inside the formatter is an
> important design feature so that we don't have to feed the formatter all the
> data at once.
> This patch comes with three implementations of the table formatter: Aligned,
> Unaligned, and JSON.
> h2. Formatter Usage Pattern
> The verbose way to use the formatter to print a table is as follows:
> 1. call start_table to reset the formatter's state and pass configuration
> options
> 2. call start_row to start writing a row
> 3. call cell to write a single cell
> 4. call close_row
> 5. call close_table
> Sometimes, it will feel like this is a lot of method calls, but these calls
> act as "hooks"
> and give each of the formatter implementations a chance to fill out all the
> content necessary
> between cells. To cut down on boilerplate, there are shortcut methods like
> row and single_value_table.
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