1、磁盘数据格式
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2、代码分析
//磁盘头初始化函数
ssd_device_header *
ssd_init_header(as_namespace *ns)
{ //header的大小是1M
ssd_device_header *h = cf_valloc(SSD_DEFAULT_HEADER_LENGTH);
if (! h) {
return 0;
}
memset(h, 0, SSD_DEFAULT_HEADER_LENGTH);
h->magic = SSD_HEADER_MAGIC;
h->random = 0;
h->write_block_size = ns->storage_write_block_size;
h->last_evict_void_time = 0;
h->version = SSD_VERSION;
h->devices_n = 0;
h->header_length = SSD_DEFAULT_HEADER_LENGTH;
memset(h->namespace, 0, sizeof(h->namespace));
strcpy(h->namespace, ns->name);
h->info_n = AS_PARTITIONS;
h->info_stride = SSD_HEADER_INFO_STRIDE;
return h;
}//记录写入的大小以128字节对齐 ssd_write_bins->r->n_rblocks = BYTES_TO_RBLOCKS(write_size); :write_size >> 7;
3、SSD模式下，刷盘是随机的
//当current_swb写满时，从ssd->swb_free_q队列获取一个空闲的swb
ssd_write_bins->swb = swb_get(ssd)->cf_queue_pop(ssd->swb_free_q, &swb, CF_QUEUE_NOWAIT)
/*
1、而ssd->swb_free_q链表里的swb并不是按磁盘从头到尾的顺序排列的
2、后台线程从脏队列拿出一个刷完后放到swb_free_q队列里
*/
ssd_write_worker->cf_queue_pop(ssd->swb_write_q, &swb, 100)->
ssd_flush_swb(ssd, swb)->ssd_post_write->swb_dereference_and_release->
swb_release->cf_queue_push(swb->ssd->swb_free_q, &swb)
//swb和磁盘的关系是1M1M对应的
ssd_flush_swb->off_t write_offset = (off_t)WBLOCK_ID_TO_BYTES(ssd, swb->wblock_id);
->lseek(fd, write_offset, SEEK_SET)
->write(fd, swb->buf, ssd->write_block_size)
static inline uint64_t WBLOCK_ID_TO_BYTES(drv_ssd *ssd, uint32_t wblock_id) {
return (uint64_t)wblock_id * (uint64_t)ssd->write_block_size;
}swb不按照磁盘从小到大进行取，刷写时磁盘可能跳来跳去，即刷写时随机写。对于普通硬盘来说性能是不容乐观的。所以Aerospike官方对于SSD模式也推荐使用SSD盘进行存储数据。
作者：yanzongshuai 发表于2018/1/4 20:57:52 原文链接
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