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Shared memory and memory context question

From: richard(at)playford(dot)net
To: pgsql-hackers(at)postgresql(dot)org
Subject: Shared memory and memory context question
Date: 2006-02-05 14:03:59
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Dear all,

I am writing a C-language shared-object file which is dynamically linked with 
postgres, and uses the various SPI functions for executing queries from 
numerous trigger functions.

My question is thus: what is the best method for a dynamically linked object 
to share memory with the same object running on other backends? Am I right in 
thinking that if I allocate memory in the "upper execution context" from 
SPI_palloc(), this is not shared with the other processes?

I thought of a few ways of doing this (please forgive me if these appear 
idiotic, as I am fairly new to postgres):

1. Change memory context to TopMemoryContext and palloc everything there. 
(However, I believe this still isn't shared between processes?)

2. Use the shmem functions in src/backend/storage/ipc/shmem.c to create a 
chunk of shared memory and use this (Although I would like to avoid writing 
my own memory manager to carve up the space).

3. Somehow create shared memory using the shmem functions, and set a memory 
context to live *inside* this shared memory, which my trigger functions can 
then switch to. Then use palloc() and pfree() without worrying..

Please let me know if this problem has been solved before, as I have searched 
through the mailing lists and through the source, but am not sure which is 
the best way to resolve it. Thanks for your help.




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Subject: Re: Shared memory and memory context question
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