I'm working on a project, whose implementation deals with PostgreSQL. A brief
description of the project is given below.
Project Description:
--------------------
In Main Memory DataBase(MMDB) entire database on the disk is loaded on to
the main memory during initial startup of the system. There after all the
references are made to database on the main memory. When the system is going
to shutdown, we will write back the database on the main memory to disk.
Here, for the sake of recovery we are writing log records on to the disk
during the transaction execution.
We want to implement MMDB by modifying PostgreSQL. We implemented our own
Main Memory File System to store the primary copy of the database in main
memory, and Modified the PostgreSQL to access the data in the Main Memory File
System.
Now, in our implementation Disk access is completely avoided during normal
transaction execution. So, we need to modify the Query Optimizer of PostgreSQL
so that it wont consider disk related costs during calculation of Query Costs.
Query Optimizer should try to minimize the Processing Cost. The criteria for
cost can be taken as the number of tuples that have to read/write from main
memory, number of comparisons, etc.
Can any one tell me the modifications needs to be incorporated to PostgreSQL,
so that it considers only Processing Costs during optimization of the Query.
In PostgreSQL, Path costs are measured in units of disk accesses. One
sequential page fetch has cost 1. I think, in PostgreSQL following paramters
are used in calculating the cost of the Query Path :
#random_page_cost = 4 # units are one sequential page fetch
cost
#cpu_tuple_cost = 0.01 # (same)
#cpu_index_tuple_cost = 0.001 # (same)
#cpu_operator_cost = 0.0025 # (same)
#effective_cache_size = 1000 # typically 8KB each
In our case we are reading pages from Main Memory File System, but not from Disk. Will it
be sufficient, if we change the default values of above paramters in
"src/include/optimizer/cost.h and
src/backend/utils/misc/postgresql.conf.sample" as follows:
random_page_cost = 4;
cpu_tuple_cost = 2;
cpu_index_tuple_cost = 0.2;
cpu_operator_cost = 0.05;
Please help us in this regard. I request all of you to give
comments/suggestions on this. Waiting for your kind help.
--
Thanks.
Anjan Kumar A.
MTech2, Comp Sci.,
www.cse.iitb.ac.in/~anjankumar
______________________________________________________________
May's Law:
The quality of correlation is inversly proportional to the density
of control. (The fewer the data points, the smoother the curves.)
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