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From "Mingfai Ma (JIRA)" <>
Subject [jira] Commented: (DROIDS-52) Optimize memory usage of TaskQueue and History
Date Thu, 18 Jun 2009 08:08:07 GMT


Mingfai Ma commented on DROIDS-52:

for the previous comment, I'm more focus on reducing memory usage. for Long instead of Date,
i mean we store the new Date().getTime() instead of the date. And from my test, it uses less
memory. Sorting will not be affected. I think there is no impact unless our date usage involves

re. URI, i have found another issue. 
 - there are possibly invalid/non-standard URI on the Internet which are usable by modern
browsers.  the following are two examples:|3.0|327|2062389|0|225|ADTECH;loc=300;grp=[group]>details&productId=1889640

  they contains illegal character according to, but if we put the link in Firefox,
it does work.

 - as you may know, Heritrix doesn't use URI but use UURI (usable URI). 

 - we probably should give up, i'm going to create another issue for this later.

> Optimize memory usage of TaskQueue and History
> ----------------------------------------------
>                 Key: DROIDS-52
>                 URL:
>             Project: Droids
>          Issue Type: Wish
>          Components: core
>    Affects Versions: 0.01
>            Reporter: Mingfai Ma
>            Priority: Minor
>         Attachments:
> Tasks in TaskQueue and History are items that has to be "persisted" in a single crawl
"session"/run. They are not consuming too much memory right now and this task is created for
tracking some optimization ideas. 
> The following is some sample memory usage figures in a 32-bit Windows Vista environment:
(refer to the attached test case)
>  - With javamex classmexer, 1M LinkTask in a queue consumes 280M of memory. 
>  - For history, stores as MD5 as String, each URL could take 104 bytes only. 1M URL takes
100M roughly. (reference:
Notice that MD5 is not guaranteed to be unique but it should be ok for general cases.
>  - To reduce memory footprint future, we may store MD5 as byte[], that take exactly 32
bytes, and will consumes 32M memory for 1M records
> Previously, I ran a job that I try to reduce the memory usage for TaskQueue, I tried
to simulate a Queue function with JBossCache that support eviction and passivation. JBossCache's
passivation mechanism basically serialize the item into a database (or other device) and unload
them from memory. It could effectively reduce memory usage. For a Queue with lots of items,
there is no need to keep them all in memory as they won't be processed at the same time anyway.
If it is necessary to keep a reference, we may passivate the LinkTask and just keep a hash
(MD5, or even hashCode()). 
> There is one more way to store the tasks in an embedded database such as H2Database.
It stores the data on disk.

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