feat(spanner): add a representation for the Spanner INTERVAL #14059

devbww · 2024-04-25T03:11:50Z

Add a C++ type, spanner::Interval, to model the Spanner INTERVAL: the difference between two date/time values.

Basic operations and string conversions are provided. Extra operations involving Date and Timestamp values are upcoming.

Integration of Interval with spanner::Value awaits the publication of the google.spanner.v1.TypeCode::INTERVAL enum value.

This change is

Add a C++ type, `spanner::Interval`, to model the Spanner `INTERVAL`: the difference between two date/time values. Basic operations and string conversions are provided. Extra operations involving `Date` and `Timestamp` values are upcoming. Integration of `Interval` with `spanner::Value` awaits the publication of the `google.spanner.v1.TypeCode::INTERVAL` enum value.

codecov · 2024-04-25T03:41:28Z

Codecov Report

Attention: Patch coverage is 99.43978% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 93.23%. Comparing base (adcfe80) to head (c749a3b).
Report is 12 commits behind head on main.

Files	Patch %	Lines
google/cloud/spanner/interval_test.cc	98.56%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14059      +/-   ##
==========================================
- Coverage   93.76%   93.23%   -0.54%     
==========================================
  Files        2281     2197      -84     
  Lines      198737   188653   -10084     
==========================================
- Hits       186353   175883   -10470     
- Misses      12384    12770     +386

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coryan

I think the Parser class needs to go, the rest of my comments I could be convinced they are misguided.

coryan · 2024-04-25T11:42:33Z

google/cloud/spanner/interval.cc

+  std::function<Interval(std::int32_t)> factory;
+} const kUnitFactories[] = {
+    // "days" is first so that it is chosen when unit is empty.
+    {"days", [](auto n) { return Interval(0, 0, n); }},


I went into a rabbit hole: PostgresQL only supports english to define intervals, I was worried that i18n would force us to parse intervals defined in French or worse.

Sacre bleu!

coryan · 2024-04-25T11:44:27Z

google/cloud/spanner/interval.h

+  std::int32_t months_;
+  std::int32_t days_;
+  absl::Duration offset_;


FWIW, this is the documented representation in Postgres:

https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-INTERVAL-INPUT:~:text=Internally%20interval%20values%20are%20stored%20as%20months%2C%20days%2C%20and%20microseconds.

Can we find any documentation to reference justifying why this is a good representation for Spanner too?

The most definitive statement I can find internally is "The GoogleSQL interval value is proposed to be logically encoded as an object with 3 fields: 1) # of months, 2) # of days, and 3) # of nanoseconds." However, the whole gist of the design docs is that the same code can handle both GoogleSQL and PostgreSQL dialects.

coryan · 2024-04-25T11:47:56Z

google/cloud/spanner/interval.h

+ * A representation of the Spanner INTERVAL type: The difference between
+ * two date/time values.
+ *
+ * @see https://cloud.google.com/spanner/docs/data-types#interval_type


This link does not work for me, not yet. The closest I can find is:

https://cloud.google.com/spanner/docs/reference/postgresql/data-types#unsupported-data-types

Yeah, not yet. Internal indications are that the link I gave will be correct when the service support is released. So our alternatives now are to make that assumption (which I chose), or to remove the link, to be re-added later. I'm happy to do the latter if you feel strongly about it.

coryan · 2024-04-25T11:48:57Z

google/cloud/spanner/interval.cc

+  // Fractional results only flow down into smaller units. Nothing ever
+  // carries up into larger units. This means that '1 month' / 2 becomes
+  // '15 days, but '1 month 15 days' * 3 is '3 months 45 days'.


Okay, but why?

Only because that is how the operation is defined (to the best of my understanding). The important takeaway is that the months/days/duration pieces should be kept distinct (seeing as they don't really inter-convert), until you have no choice. For example, addition and negation are field-by-field, but the alternative here would be that "1 month" / 2 is zero, and I guess that was deemed worse.

If there is a go/ link or something, maybe add that as a comment. Otherwise, SGTM.

That particular example, albeit written as "1 month" * 0.5, comes from https://gist.github.com/henryivesjones/ebd653acbf61cb408380a49659e2be97, which is cited near the test of that case.

Internally there is a "1 day" / 2 -> "12 hours" example in go/spangres-interval-design, but I hesitate to mention that in the code.

coryan · 2024-04-25T12:22:27Z

google/cloud/spanner/interval.cc

+StatusOr<Interval> Parser::Parse() {
+  Interval intvl;
+  auto s = absl::string_view(s_);


Do you even need the Parser class? This is the only place you use s_, and it seems you could just say:

StatusOr<Interval> ParseInterval(std::string s_) { Interval intvl; auto s = absl::string_view(s_); ...

Parser had additional data members before. But even after simplification to this state, I kept the class as an intra-file visibility barrier (the helpers being private). But I acknowledge that there is disagreement about such tactics, so I'm happy to remove. Done.

google/cloud/spanner/interval.cc

google/cloud/spanner/interval_test.cc

devbww

Thanks.

I think the Parser class needs to go

Done.

the rest of my comments I could be convinced they are misguided.

Some heeded; some countered.

devbww · 2024-04-26T19:53:22Z

google/cloud/spanner/interval.cc

+  std::function<Interval(std::int32_t)> factory;
+} const kUnitFactories[] = {
+    // "days" is first so that it is chosen when unit is empty.
+    {"days", [](auto n) { return Interval(0, 0, n); }},


Sacre bleu!

google/cloud/spanner/interval.cc

devbww · 2024-04-26T19:58:53Z

google/cloud/spanner/interval.cc

+StatusOr<Interval> Parser::Parse() {
+  Interval intvl;
+  auto s = absl::string_view(s_);


Parser had additional data members before. But even after simplification to this state, I kept the class as an intra-file visibility barrier (the helpers being private). But I acknowledge that there is disagreement about such tactics, so I'm happy to remove. Done.

devbww · 2024-04-26T20:05:58Z

google/cloud/spanner/interval.cc

+  // Fractional results only flow down into smaller units. Nothing ever
+  // carries up into larger units. This means that '1 month' / 2 becomes
+  // '15 days, but '1 month 15 days' * 3 is '3 months 45 days'.


Only because that is how the operation is defined (to the best of my understanding). The important takeaway is that the months/days/duration pieces should be kept distinct (seeing as they don't really inter-convert), until you have no choice. For example, addition and negation are field-by-field, but the alternative here would be that "1 month" / 2 is zero, and I guess that was deemed worse.

devbww · 2024-04-26T20:11:09Z

google/cloud/spanner/interval.h

+ * A representation of the Spanner INTERVAL type: The difference between
+ * two date/time values.
+ *
+ * @see https://cloud.google.com/spanner/docs/data-types#interval_type


Yeah, not yet. Internal indications are that the link I gave will be correct when the service support is released. So our alternatives now are to make that assumption (which I chose), or to remove the link, to be re-added later. I'm happy to do the latter if you feel strongly about it.

devbww · 2024-04-26T20:14:54Z

google/cloud/spanner/interval.h

+  std::int32_t months_;
+  std::int32_t days_;
+  absl::Duration offset_;


The most definitive statement I can find internally is "The GoogleSQL interval value is proposed to be logically encoded as an object with 3 fields: 1) # of months, 2) # of days, and 3) # of nanoseconds." However, the whole gist of the design docs is that the same code can handle both GoogleSQL and PostgreSQL dialects.

google/cloud/spanner/interval_test.cc

coryan · 2024-04-26T20:23:42Z

google/cloud/spanner/interval.cc

+  // Fractional results only flow down into smaller units. Nothing ever
+  // carries up into larger units. This means that '1 month' / 2 becomes
+  // '15 days, but '1 month 15 days' * 3 is '3 months 45 days'.


If there is a go/ link or something, maybe add that as a comment. Otherwise, SGTM.

An update to the `Interval` API introduced in googleapis#14059. Use `std::chrono::nanoseconds` instead of `absl::Duration` to represent the absolute "offset" portion of the interval.

An update to the `Interval` API introduced in #14059. Use `std::chrono::nanoseconds` instead of `absl::Duration` to represent the absolute "offset" portion of the interval.

An update to the `Interval` API introduced in googleapis#14059. Use `std::chrono::nanoseconds` instead of `absl::Duration` to represent the absolute "offset" portion of the interval.

devbww temporarily deployed to internal April 25, 2024 03:11 — with GitHub Actions Inactive

product-auto-label bot added the api: spanner Issues related to the Spanner API. label Apr 25, 2024

comma -> semi-colon

736e1d2

devbww temporarily deployed to internal April 25, 2024 03:58 — with GitHub Actions Inactive

devbww marked this pull request as ready for review April 25, 2024 05:46

devbww requested a review from a team as a code owner April 25, 2024 05:46

coryan suggested changes Apr 25, 2024

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devbww commented Apr 26, 2024

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Address review comments

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devbww temporarily deployed to internal April 26, 2024 20:21 — with GitHub Actions Inactive

coryan approved these changes Apr 26, 2024

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Fix typo

c749a3b

devbww temporarily deployed to internal April 26, 2024 21:17 — with GitHub Actions Inactive

devbww merged commit 10c07f6 into googleapis:main Apr 26, 2024
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devbww deleted the interval-type branch April 26, 2024 23:16

devbww mentioned this pull request Apr 30, 2024

fix(spanner): avoid absl types in public Interval API #14095

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feat(spanner): add a representation for the Spanner INTERVAL #14059

feat(spanner): add a representation for the Spanner INTERVAL #14059

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feat(spanner): add a representation for the Spanner INTERVAL #14059

feat(spanner): add a representation for the Spanner INTERVAL #14059

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devbww commented Apr 25, 2024 •

edited by coryan

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