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https://issues.apache.org/jira/browse/HBASE-24901?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Elliot Miller updated HBASE-24901:
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Attachment: HBase Shell Default TableFormatter hb9e903.png
> 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, HBase Shell
> Default TableFormatter hb9e903.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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