Re: Some indexing advice for a Postgres newbie, please?

On Sat, Feb 21, 2015 at 5:33 AM, Arjen Nienhuis <a(dot)g(dot)nienhuis(at)gmail(dot)com> wrote:
> Hi,
>
> On 19 Feb 2015 17:12, "brian" <brian(at)meadows(dot)pair(dot)com> wrote:
>>
>>
>> Hi folks,
>>
>> I have a single-user application which is growing beyond the
>> fixed-format data files in which it currently holds its data, I need a
>> proper database as the backend. The front end is written using Lazarus
>> and FreePascal under Linux, should anyone feel that makes a
>> difference. The database will need to grow to around 250,000 records.
>>
>> My problem is with the data field which is the (unique) key. It's
>> really a single 192-bit integer (it holds various bits of bitmapped
>> data) which I currently hold as six 32-bit integers, but can convert
>> if needed when transferring the data.
>>
>> How would you advise that I hold this field in a Postgres database,
>> given the requirement for the whole thing to be a unique key? The
>> first 64 bits change relatively infrequently, the last 128 bits will
>> change with virtually every record. The last 128 bits will ALMOST be
>> unique in themselves, but not quite. :(
>>
>> Thanks,
>>
>> Brian.
>>
>
> Postgres can use almost anything as a key so it probably depends on the
> library you use to access the database.
>
> If it supports "composite primary keys" you can use the 6 ints as a key:
>
> PRIMARY KEY (n1, n2, n3, n4, n5, n6)
>
> The numeric type can hold 192-bit numbers. I think Lazarus supports this as
> well.
>
> You could also use a surrogate key and define a UNIQUE constraint on the 6
> ints or the 192-bit number.

You could also use 3 64 bit bigints if that's easier. The other way
to do it is bytea.

merlin