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https://issues.apache.org/jira/browse/CASSANDRA-19546?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Cheng Wang updated CASSANDRA-19546:
-----------------------------------
Authors: Cheng Wang, Stefan Miklosovic (was: Cheng Wang)
> Add format_bytes and format_time functions
> ------------------------------------------
>
> Key: CASSANDRA-19546
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19546
> Project: Apache Cassandra
> Issue Type: New Feature
> Components: Legacy/CQL
> Reporter: Stefan Miklosovic
> Assignee: Cheng Wang
> Priority: Normal
> Fix For: 5.x
>
> Time Spent: 3h 50m
> Remaining Estimate: 0h
>
> There are cases (e.g in our system_views tables but might be applicable for
> user tables as well) when a column is of a type which represents number of
> bytes. However, it is quite hard to parse a value for a human to have some
> estimation what that value is. This function looks at values in a column as
> if it was in bytes, and it will convert it to whatever a user pleases.
> Supported units are: {{{}B{}}}, {{{}KiB{}}}, {{MiB}} and {{{}GiB{}}}. The
> result will be rounded to two decimal places.
> I propose this:
> {code:java}
> CREATE TABLE ks.tb (
> id int PRIMARY KEY,
> val bigint
> ) {code}
>
> {code:java}
> cqlsh> select * from ks.tb;
> id | val
> ----+----------------
> 5 | 60000
> 1 | 1234234
> 2 | 12342341234234
> 4 | 60001
> 7 | null
> 6 | 43
> 3 | 123423 {code}
> {code:java}
> cqlsh> select format_bytes(val) from ks.tb;
> system.format_bytes(val)
> --------------------------
> 58.59 KiB
> 1.18 MiB
> 11494.7 GiB
> 58.59 KiB
> null
> 43 B
> 120.53 KiB{code}
> I also propose that this format_bytes function (name of it might be indeed
> discussed and it is just a suggestion) should be only applicable for int,
> smallint, bigint and varint types. I am not sure how to apply this to e.g.
> "float" or similar. As I mentioned, it is meant to convert just number of
> bytes, which is just some number, to a string representation of that and I do
> not think that applying that function to anything else but these types makes
> sense.
> The second way to call {{format_bytes}} functions is to specify into what
> size unit we would like to see all values to be converted to. For example, we
> want all size to be represented in mebibytes, hence we do:
> {code:java}
> cqlsh> select format_bytes(val, 'MiB') from ks.tb;
> system.format_bytes(val, 'MiB')
> ----------------------------------
> 0.06 MiB
> 1.18 MiB
> 11770573.84 MiB
> 0.06 MiB
> null
> 0 MiB
> 0.12 MiB {code}
> Lastly, we can specify a source unit and a target unit. A source unit tells
> what unit that column is logically of, the target unit tells what unit we
> want these values to be converted to. For example, if we know that our column
> is logically in kibibytes and we want them to be converted into mebibytes, we
> would do:
>
> {code:java}
> cqlsh> select format_bytes(val, 'Kib', 'MiB') from ks.tb;
> system.format_bytes(val, 'KiB', 'MiB')
> ----------------------------------------
> 58.59 MiB
> 1205.31 MiB
> 12053067611.56 MiB
> 58.59 MiB
> null
> 0.04 MiB
> 120.53 MiB {code}
>
>
> Similarly to {*}{{format_bytes}}{*}, we can do transformations on
> duration-like columns, namely {*}format_time{*}.
> Supported units are: {{{}d{}}}, {{{}h{}}}, {{{}m{}}}, {{{}s{}}}, {{{}ms{}}},
> {{{}us{}}}, {{{}µs{}}}, {{{}ns{}}}. Supported column types on which this
> function is possible to be applied: {{{}INT{}}}, {{{}TINYINT{}}},
> {{{}SMALLINT{}}}, {{{}BIGINT{}}}, {{{}VARINT{}}}, {{{}ASCII{}}},
> {{{}TEXT{}}}. For {{ASCII}} and {{TEXT}} types, text of such column has to be
> a non-negative number. The result will be rounded to two decimal places.
> {code:java}
> cqlsh> select format_time(val) from ks.tb;
> system.format_time(val)
> -------------------------
> 1 m
> 20.57 m
> 142851.17 d
> 1 m
> null
> 43 ms
> 2.06 m {code}
> We may specify what unit we want that value to be converted to, give the
> column’s values are in milliseconds:
> {code:java}
> cqlsh> select format_time(val, 'm') from ks.tb;
> system.format_time(val, 'm')
> ------------------------------
> 1 m
> 20.57 m
> 205705687.24 m
> 1 m
> null
> 0 m
> 2.06 m {code}
> Lastly, we can specify both source and target values:
> {code:java}
> cqlsh> select format_time(val, 's', 'h') from ks.tb;
> system.format_time(val, 's', 'h')
> -----------------------------------
> 16.67 h
> 342.84 h
> 3428428120.62 h
> 16.67 h
> null
> 0.01 h
> 34.28 h {code}
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