[Glass] Position method for BtreePlusReadStream classes

[smalltalk at adinet.com.uy]

Dale,

That’s exactly was I looking for. A public method in next release it will good too, 
Thank very much...

----- Mensaje original -----
De: Dale Henrichs via Glass <glass at lists.gemtalksystems.com>
Para: glass at lists.gemtalksystems.com
Enviado: Mon, 08 Jun 2020 19:35:37 -0300 (UYT)
Asunto: Re: [Glass] Position method for BtreePlusReadStream classes

Bruno,

Sorry, I wasn't sure what you were asking ... but now that you mention 
it, there is already a method that will advance the stream cursor, 
without accessing the object at that position (_btreeNextNoValue)

    [ stream atEnd not and: [ pos < collectionSize ] ]
       whileTrue: [
         pos := pos + 1.
         stream _btreeNextNoValue ]

If you want to count backward from the end using a reversedReadStream, 
then you'd have to implement _btreePreviousNoValue:

    _btreePreviousNoValue
       "Returns the next value on a stream of B-tree values and root objects.  Updates the current
      stack for a subsequent 'next'."

       | val |
       " get the index into the leaf node and see if it has reached the end "
       currentIndex == 0
         ifTrue: [ ^ self _errorEndOfStream ].	" get the leaf and the value within the leaf "
       (currentNode == endNode and: [ endIndex == currentIndex ])
         ifTrue: [
           currentIndex := 0.
           ^ self ].	" see if index refers to first entry in this leaf "
       currentIndex == 1
         ifTrue: [
           " must look down the stack for the next leaf node "
           self _previousLeaf ]
         ifFalse: [ currentIndex := currentIndex - currentEntrySize ].

_btreeNextNoValue and _btreePreviousNoValue both avoid faulting the 
values into the image, just the interior and leaf nodes would be faulted 
in gut that is unavoidable ...

If the these would work for you I can see adding skip: to both 
BtreePlusGsIndexReadStream and BtreePlusGsReversedIndexReadStream to 
make it official ... let me know if this is what you are looking for,

Dale

On 6/8/20 1:11 PM, bruno buzzi brassesco via Glass wrote:
>
> Dale,
>
> Which is the difference of your solution with the following ?
> btreePlusReadStream := gsQuery reversedReadStream.
> position := 1.
> [btreePlusReadStream atEnd not and: [position < collectionSize]] 
> whileTrue: [btreePlusReadStream next. position := position + 1].
>
> What i want is to have a very large (a millon ?) GsQuery result set 
> (in index order) and go to a position (K) without faulting into memory 
> objects previous to the (K) position.
>
> regards
> bruno
>
> On 8/6/2020 16:18, Dale Henrichs via Glass wrote:
>>
>> Bruno,
>>
>> There is no backing collection for the BtreePlusReadStream, so being 
>> able to go to a certain position is not possible without counting....
>>
>> We should be able to quickly produce a result set of the entire query 
>> results, but it would be a set not an ordered collection:( And to get 
>> results _in order_ the streaming API is the only solution... To get 
>> the kind of performance that you would want, I would think that it 
>> should be possible to create a primitive that would produce the 
>> result set in the form of an Array (in order) instead of a Set.
>>
>> For now you would have to produce the Array yourself using:
>>
>>     | result |
>>     result := {}.
>>     gsQuery do: [:each | result add: each]
>>
>> #do: uses the BtreePlusReadStream api underneath covers, so the #do: 
>> elements are processed in order ...
>>
>> Let me know if you you would need a primitive for performance and I 
>> can submit a feature request ...
>>
>> Dale
>>
>> On 6/8/20 11:53 AM, smalltalk--- via Glass wrote:
>>> Hi,
>>>
>>> aRcIdentitySet has an index on 'each.modifiedTime' and it can have a 
>>> lot of instances.
>>>
>>> In order to get a list of sorted instances (by modifiedTime) i do:
>>> |gsQuery|
>>> gsQuery := GsQuery fromString: 'each.modifiedTime <= timeNow'.
>>> gsQuery bind: 'timeNow' to: TimeStamp now.
>>> gsQuery on: aRcIdentitySet .
>>>
>>> Now i want to 'jump' to a given position in this stream...
>>> It is possible to use some kind of #position: message in 
>>> aBtreePlusReadStream ?
>>> (position: does no exist in BtreePlusReadStream)
>>>
>>> I could use #next to 'jump' to a given position, but the query can 
>>> be very very large.
>>> At the end it show a paging web page to a user that can click to get 
>>> the next bunch of objects.
>>> So i do not want to do #next over a large collection.
>>>
>>> regards,
>>> bruno
>>> 2.11.0.0
>>> 2.11.0.0
>>>
>>> _______________________________________________
>>> Glass mailing list
>>> Glass at lists.gemtalksystems.com
>>> https://lists.gemtalksystems.com/mailman/listinfo/glass
>>
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