关于postgre 内存的使用

temp_buffer和shared_buffers是分开的.
GUC

        {
                {"temp_buffers", PGC_USERSET, RESOURCES_MEM,
                        gettext_noop("Sets the maximum number of temporary buffers used by each session."),
                        NULL,
                        GUC_UNIT_BLOCKS
                },
                &num_temp_buffers,
                1024, 100, INT_MAX / 2,
                check_temp_buffers, NULL, NULL
        },

申请代码

/*
 * InitLocalBuffers -
 *        init the local buffer cache. Since most queries (esp. multi-user ones)
 *        don't involve local buffers, we delay allocating actual memory for the
 *        buffers until we need them; just make the buffer headers here.
 */
static void
InitLocalBuffers(void)
{
        int                     nbufs = num_temp_buffers;
        HASHCTL         info;
        int                     i;

        /* Allocate and zero buffer headers and auxiliary arrays */
        LocalBufferDescriptors = (BufferDesc *) calloc(nbufs, sizeof(BufferDesc));
        LocalBufferBlockPointers = (Block *) calloc(nbufs, sizeof(Block));
        LocalRefCount = (int32 *) calloc(nbufs, sizeof(int32));
        if (!LocalBufferDescriptors || !LocalBufferBlockPointers || !LocalRefCount)
                ereport(FATAL,
                                (errcode(ERRCODE_OUT_OF_MEMORY),
                                 errmsg("out of memory")));

        nextFreeLocalBuf = 0;

        /* initialize fields that need to start off nonzero */
        for (i = 0; i < nbufs; i++)
        {
                BufferDesc *buf = &LocalBufferDescriptors[i];

                /*
                 * negative to indicate local buffer. This is tricky: shared buffers
                 * start with 0. We have to start with -2. (Note that the routine
                 * BufferDescriptorGetBuffer adds 1 to buf_id so our first buffer id
                 * is -1.)
                 */
                buf->buf_id = -i - 2;
        }

        /* Create the lookup hash table */
        MemSet(&info, 0, sizeof(info));
        info.keysize = sizeof(BufferTag);
        info.entrysize = sizeof(LocalBufferLookupEnt);
        info.hash = tag_hash;

        LocalBufHash = hash_create("Local Buffer Lookup Table",
                                                           nbufs,
                                                           &info,
                                                           HASH_ELEM | HASH_FUNCTION);

        if (!LocalBufHash)
                elog(ERROR, "could not initialize local buffer hash table");

        /* Initialization done, mark buffers allocated */
        NLocBuffer = nbufs;
}

十分感谢指教。我们公司也是阿里云用户，哈哈，

@明虚 感谢回复。
shared_buffers 是哪些会用到？ 我看了很多网站是建议 物理内存的 1/4 - 1/5，
我不明白具体是什么会用到，设置什么才是会符合我们的业务。

tmp_buffers，也就是pg代码里面的local buffers，各个backend是不需要共享这部分内存的，所以这部分内存是在需要的时候malloc的私有内存，非shared_buffers内存。