Hi,
I recently stumbled into some performance issue I had, so I profiled
it and got it fixed, but by doing that I also noticed a huge time
spent when reading DateAndTimes and Dates (which also uses the former)
and the culprit seems to be `Date class>>#readFrom:`.
Digging into this, I noticed that this was called from
`DateAndTime>>#readFrom:`, but in particular 90% of the time spent was
when instantiating the Date part of it, because it does unnecessary
lookup of the index of Month when input stream only have a month
index.
What I did then was to change the default behavior of DateAndTime
class>>#readFrom:
readFrom: aStream defaultOffset: defaultOffset
"Parse and return a new DateAndTime instance from stream,
as a Date, an optional Time and an optional TimeZone offset.
The time defaults to midnight, the timezone to defaultOffset"
"self readFrom: '2013-03-04T23:47:52.876+01:00' readStream"
"From this"
date := Date readFrom: aStream.
"To this"
date := Date readFrom: (aStream next: 10) pattern: 'yyyy-mm-dd'.
And also in P3Converter to specify the pattern directly.
P3Converter>>#convertDateFrom: bytes length: length description: description
^Date readFrom: (self asciiStreamFor: bytes length: length) pattern:
'yyyy-mm-dd'
With these two changes I got a 8x-10x speedup when reading
Date/DateAndTime from the database.
Then I dig a little further and in P3Converter added a little check to
avoid translating the offset of a DateAndTime when it is not needed.
P3Converter>>#convertDateAndTimeWithoutTimezoneFrom: bytes length:
length description: description
"TIMESTAMP WITHOUT TIME ZONE (TIMESTAMP) is stored internally in
Postgres the way it was inserted, its representation remains constant,
with no offset added. We use the timezone of the connection to do the
necessary shifting. This assumes that the timezones used during
insert/update and query are the same."
| timestamp offset |
timestamp := DateAndTime readFrom: (self asciiStreamFor: bytes
length: length) defaultOffset: Duration zero.
offset := self timezone offsetForTimestamp: timestamp.
^offset isZero "<-- added this check to avoid translation"
ifTrue: [ timestamp ]
ifFalse: [ timestamp translateTo: offset ]
And the speedup went even higher. But I don't know whether this last
part is correct.
Of course this seems as a quick and dirty fix, but I don't know
whether DateAndTime>>readFrom: should read any format or just ISO 8601
formats nor whether the Date/DateAndTime coming from PostgreSQL are
always formatted that way. I ran my app's small test suite and haven't
had any issues, neither during development with these changes applied.
I think there is a significant slowdown involved in the instantiation
of Dates that should be fixed, whether this fix is definitive or not
is why I'm asking here.
Regards!
Esteban A. Maringolo
