[SQU] Memory usage breakdown (and MEM_REQUEST_T/request_t memory)

I've been looking at two Squid systems which are identical in all
respects (exactly the same Solaris OS build, patches) including Squid
2.2 STABLE 4, and configuration installed from the same package (as
built by myself.)

They're configured as accelerators, have been running for the same
amount of time, and have serviced approximately the same number of
requests. They are both utilising redirector processes. But their
memory usage is radically different.

Here are some key values, taken from the process tables and from the
'mem' cache info.

          RSS Storage Store Storage StoreEntry SM
                  swap entries Mem memory buf
host-a 255MB 1349921kB 105024 124696kB 5747kB 124940kB
host-b 1098MB 1166827kB 131280 614360kB 7183kB 796248kB

        Hotcache Store Entries on-disk Mem request_t
         items with Mem Objects objects obj
host-a 23747 23753 80657 2694kB 189kB
host-b 1903 73218 69759 8298kB 80146kB

         short medium long
        strings strings strings
host-a 7265kB 326kB 17kB
host-b 42816kB 26664kB 6077kB

Both hosts have 2GB of RAM (cache_mem is set to 600MB), and they're
running well within the memory of the machine. Both have a max
cache_dir size of 2560MB, and are running with the default 13kB
average object size estimate (stats report approx 16.75kB on each.)

It's the big descrepancy between the numbers of "Store Entries with
Memory Objects" and the resultant memory consumption (host-b being
over 3 times the size of host-a, tying up approx 600MB/780MB of RAM in
Storage Memory/Storage Memory Buffers) that puzzles me.

Why are so many more objects stored in memory on host-b (and what is
the difference between that and the Hostcache items)? Why might there
be such a large amount of memory allocated to request_t on host-b
compared to host-a? Both had an approximately equal number of current
sessions at the time when I took these figures.

Are there any other numbers I should look at? (I have the full snapshot
output of the 'info' and 'mem' cache_info pages for both systems.)

James.

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