feat: ignoring time zone info when import from external files

[v0y4g3r]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR allows users to import parquet files with explicit time zone info in schema by ignoring the time zone info and treating the i64 value as time elapsed since UNIX epoch.

Why ignoring time zone in arrow array is correct?

According to Timezone Aware Timestamp Parsing - arrow-rs, the time zone info in schema is an indicator of the desired time zone, but the underlying value (the i64 value) is always adjusted to UTC time.

That is being to say, if we can a timestamp in secinds with value 28800 (86060) and time zone "+08:00", what is the UTC time point of this timestamp? Is it "1970-01:01 00:00:00"? Actually no, it "1970-01:01 08:00:00" in UTC and "1970-01:01 16:00:00" in CST.

use arrow_array::timezone::Tz;
#[test]
fn test_parsing_timestamp_to_arrow_array() {
    let arr = TimestampSecondArray::from(vec![28800]).with_timezone("+08:00".to_string());
    let tz: Tz = arr.timezone().unwrap().parse().unwrap();

    println!(
        "Timestamp with time zone: {:?}",
        arr.value_as_datetime_with_tz(0, tz).unwrap().to_string()
    );
}

// it prints: "1970-01-01 16:00:00 +08:00"

Why ignoring time zone in parquet schema is ok?

Parquet has an "isAdjustedToUTC" flag which indicates if the INT96 value in Parquet is already adjusted to UTC time, but arrow/parquet does not provide a method to read that flag. So we can only ignore the flag and treat all INT96 values in parquet's timestamp columns as timestamp relative to UTC time, just like

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

#1319

[fengjiachun]

lgtm

[codecov]

Codecov Report

Merging #1341 (acb839c) into develop (c850e96) will decrease coverage by 0.43%.
The diff coverage is 83.66%.

@@             Coverage Diff             @@
##           develop    #1341      +/-   ##
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- Coverage    85.90%   85.48%   -0.43%     
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  Files          509      509              
  Lines        76889    77032     +143     
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- Hits         66052    65849     -203     
- Misses       10837    11183     +346