[Glass] Position method for BtreePlusReadStream classes

[Dale Henrichs]

Bruno,

I've submitted an internal feature request (48811), so keep your eyse 
peeled.

Dale

On 6/9/20 9:20 AM, smalltalk--- via Glass wrote:
> 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
>>>>
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