On memcached version 1.4.5-1ubuntu1, there are two entries for the ‘- I’ parameter in the memcached(1) man page.
-I Override the size of each slab page in bytes. In mundane words, it adjusts the maximum item size that memcached will accept. You can use the suffixes K and M to specify the size as well, so use 2000000 or 2000K or 2M if you want a maximum size of 2 MB per object. It is not recommended to raise this limit above 1MB due just to performance reasons. The default value is 1 MB. -I <size> Override the default size of each slab page. Default is 1mb. Default is 1m, minimum is 1k, max is 128m. Adjusting this value changes the item size limit. Beware that this also increases the number of slabs (use -v to view), and the overal memory usage of memcached. It seems to me that the first entry is misleading. The parameter does not "adjust the maximum item size;" rather, the parameter adjusts the slab page size, and the number of items stored in each slab page. These two entries should be combined into one entry. The second entry could be further clarified by saying that reducing the page size below the 1 megabyte default page size will result in an increased number of slabs. By the way, '-I 10M' does not work. Neither does '-I 10m'. I discovered that you have to specify the byte size, i.e., '-I 10485760'. Please correct my understanding, if I am missing something. Also, I do not understand the warning, "It is not recommended to raise this limit above 1MB due just to performance reasons." What exactly are the performance issues? If my default chunk size is 480 bytes and if I am storing items in 416 byte chunks and 448 byte chunks, then, I can store more chunks in 10 megabytes pages than I can in 10 kilobyte pages. So, why wouldn't I opt to store my chunks in 10 megabyte pages (rather than 10 kilobyte pages or even 1 megabyte pages)? The vast majority of my chunks are 448 byte chunks. So, it seems to me that I can use my memory more efficiently by opting for 10 megabyte slab pages. What, if anything, is behind the "peformance" warning? Thank you for your help. David
