Re: Is there any method to keep table in memory at startup - Mailing list pgsql-hackers

Vinay Jain wrote:
> Hi
> thanx and sorry that I asked such a simple question in postgres-hackers 
> list....
> but the complexity which i feel on that basis ....please allow me to 
> explain my problem further.....
> As i am working on sorting order , length and substring functions for 
> Hindi text(Indian Language)...
> Here is the problem which i found in postgresql...
> after setting collating sequence in proper way(i.e. C) the order was on 
> basis of unicode values...but in Hindi Language some of combined unicode 
> values makes a single character
> similarly length is not appropriate for these reasons & hence substring 
> operations
> so i designed a customized data type called IndChar....and operations on it
> in order by statement the only function called is indchar_lt(defined for 
> < operator)......

Is your indchar_lt function declared IMMUTABLE? That would allow it's 
results to be cached instead of re-calculated every time.

> Now please guide me where is starting(where i can open connection to 
> database) and ending of my program....I feel only in indchar_lt function 
> which will be called many times in order by statement causing 
> performance degradation..

Have you created an index on that column? That would be a usual way to 
speed up an ORDER BY. NB, the function involved must be IMMUTABLE to be 
used in an index.

> as i am not much experienced this assumption may be wrong...

My professor at University used to always say "measure measure measure".  Postgres makes it easy to measure. Try
puttingEXPLAIN ANALYZE before 
 
your SELECT statement. Run the SELECT a couple of times first so that 
the OS can get stuff cached, then:

do an EXPLAIN ANALYZE on the query, save the results

then ANALYZE the tables involved and to another EXPLAIN ANALYZE on the 
query, save the results

add the necessary index, ANALYZE then EXPLAIN ANALYZE.

> so my question remains as it is that is there any such thing which can 
> be called at startup of psql.........to make connection to database

I'm really not sure what you mean by this. psql connects to the database 
on startup.

> regards
> Vinay
> 
> 
> 
> 
> Andrew Hammond wrote:
> 
>> Vinay Jain wrote:
>>
>>> Hi
>>>    thank you for such a useful information...
>>>    but actually in my case if i keep table in disk it  significantly 
>>> degrades performance and even for a table of  10 rows it takes 1-2 
>>> minutes I think u r not beliving it ! am i right
>>> for example
>>> I create a table in which i use my customized data type say student
>>> create table student
>>> (Name INDCHAR //INDCHAR is customized data type
>>>    age integer);
>>> now i give query like this
>>> select * from student order by name;
>>> it will search for it's comparator operator (<) and related function...
>>> in that function there is one lookup table if that table is in memory 
>>> no problem! (oh but it can't be) if it is in disk  my program makes 
>>> connection to database and execute query which is  just a select 
>>> statement on a simple where condition of equality. then closes 
>>> connection
>>
>>
>>
>> There's your problem. Creating database connections is an expensive 
>> operation. They are not intended to be opened and closed often or 
>> quickly. Open your database connection at the beginning of your 
>> program, and close it at the end.
>>
>> You could also throw an index on the column you're using in your order 
>> by clause, but that won't make a difference until your table get a 
>> little bigger.
>>
>> Please take further questions of this nature to the pgsql-novice list.
>>
>>> so every time less than operator(<) is called it does the same task..
>>> what i feel in table of 10 rows how many times the < operator will be 
>>> called(NO idea but must be > 10 times)
>>> is there any solution..
>>> thanks in advance
>>> regards
>>> vinay
>>
>>
>>
>>
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> 
> 
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