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https://issues.apache.org/jira/browse/PIG-3341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13672719#comment-13672719
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pat chan commented on PIG-3341:
-------------------------------
Before making the fix, I think there needs to be a little more clarity around
exactly what formats are supported. For example, pig 0.11.1 currently supports
datetime strings with no date - "T00:00:00" produces a date in 1970. Is this
intentional?
The general issue is that the actual implementation supports many more formats
than is specified in the iso8601 profile http://www.w3.org/TR/NOTE-datetime.
What is the specified policy regarding these extra formats? I see three choices:
1. specify precisely the entire range of supported formats. In the
implementation I submitted above, the spec (taken from joda docs) is:
date-opt-time = date-element ['T' [time-element] [offset]]
date-element = std-date-element | ord-date-element | week-date-element
std-date-element = yyyy ['-' MM ['-' dd]]
ord-date-element = yyyy ['-' DDD]
week-date-element = xxxx '-W' ww ['-' e]
time-element = HH [minute-element] | [fraction]
minute-element = ':' mm [second-element] | [fraction]
second-element = ':' ss [fraction]
fraction = ('.' | ',') digit+
2. state that the implementation may parse formats beyond the w3c profile but
such formats may not be supported in future releases.
3. run all dates through a regex that matches exactly the w3c profile and dates
that don't conform to the format are turned into null.
> Improving performance of loading datetime values
> ------------------------------------------------
>
> Key: PIG-3341
> URL: https://issues.apache.org/jira/browse/PIG-3341
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Affects Versions: 0.11.1
> Reporter: pat chan
> Priority: Minor
> Fix For: 0.12, 0.11.2
>
>
> The performance of loading datetime values can be improved by about 25% by
> moving a single line in ToDate.java:
> public static DateTimeZone extractDateTimeZone(String dtStr) {
> Pattern pattern =
> Pattern.compile("(Z|(?<=(T[0-9\\.:]{0,12}))((\\+|-)\\d{2}(:?\\d{2})?))$");;
> should become:
> static Pattern pattern =
> Pattern.compile("(Z|(?<=(T[0-9\\.:]{0,12}))((\\+|-)\\d{2}(:?\\d{2})?))$");
> public static DateTimeZone extractDateTimeZone(String dtStr) {
> There is no need to recompile the regular expression for every value. I'm not
> sure if this function is ever called concurrently, but Pattern objects are
> thread-safe anyways.
> As a test, I created a file of 10M timestamps:
> for i in 0..10000000
> puts '2000-01-01T00:00:00+23'
> end
> I then ran this script:
> grunt> A = load 'data' as (a:datetime); B = filter A by a is null; dump B;
> Before the change it took 160s.
> After the change, the script took 120s.
> ----------------
> Another performance improvement can be made for invalid datetime values. If a
> datetime value is invalid, an exception is created and thrown, which is a
> costly way to fail a validity check. To test the performance impact, I
> created 10M invalid datetime values:
> for i in 0..10000000
> puts '2000-99-01T00:00:00+23'
> end
> In this test, the regex pattern was always recompiled. I then ran this script:
> grunt> A = load 'data' as (a:datetime); B = filter A by a is not null; dump
> B;
> The script took 190s.
> I understand this could be considered an edge case and might not be worth
> changing. However, if there are use cases where invalid dates are part of
> normal processing, then you might consider fixing this.
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