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Asked: 2026-05-27T03:24:25+00:00

Several months ago I implemented a solution to choose unique values from a range

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Several months ago I implemented a solution to choose unique values from a range between 1 and 65535 (16 bits). This range is used to generate unique Route Targets suffixes, which for this customer massive network (it’s a huge ISP) are a very disputed resource, so any released value needs to become immediately available to the end user.

To tackle this requirement I used a BitSet. Allocate a suffix on the RT index with set and deallocate a suffix with clear. The method nextClearBit() can find the next available value. I handle synchronization / concurrency issues manually.

This works pretty well for a small range… The entire index is small (around 10k), it is blazing fast and can be easy serialized and stored in a blob field.

The problem is, some new devices can handle RT suffixes of 32 bits unsigned (range 1 / 4294967296). Which can’t be managed with a BitSet (it would, by itself, consume around 600Mb, plus be limited to int – 32 bits signed – range). Even with this massive range available, the client still wants to free Route Target suffixes that become available to the end user, mainly because the lowest ones (up to 65535) – which are compatible with old routers – are being heavily disputed.

Before I tell the customer that this is impossible and he will have to conform with my reusable index for lower RTs (up to 65550) and use a database sequence for the other ones (which means that when the user frees a Route Target, it will not become available again), would anyone shed some light?

Maybe some kind soul already implemented a high performance number pool for Java (6 if it matters), or I am missing a killer feature of Oracle database (11R2 if it matters)… Just some wishful thinking :).

Thank you very much in advance.

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1 Answer

  1. Editorial Team

    I would combine the following:

    your current BitSet solution for 1-65535

    PLUS

    Oracle-based solution with a sequence for 65536 – 4294967296 which wraps around defined as 

    CREATE SEQUENCE MyIDSequence
MINVALUE 65536 
MAXVALUE 4294967296 
START WITH 65536
INCREMENT BY 1
CYCLE
NOCACHE
ORDER;

    This sequence gives you ordered values in the specified range and allows for reuse of any values but only after the maximum is reached – which should allow enough time for the values being released… if need be you can keep track of values in use in a table and just increment further if the returned value is already in use – all this can be wrapped nicely into a stored procedure for convenience…

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