Squid_ The Definitive Guide - Duane Wessels [143]
Files queued for open
This value will always be zero, unless you are using the aufs storage scheme (see Section 8.4). It shows how many file-open requests have been dispatched to the thread processes but have not yet returned. aufs is the only storage scheme in which disk file descriptors are opened asynchronously.[2]
Available number of file descriptors
The number of available descriptors is the maximum, minus the number currently open and the number queued for open. It represents the amount of breathing room Squid has to handle more load. When the available number gets close to the reserved number (next line), Squid stops accepting new connections so that existing transactions continue receiving service.
Reserved number of file descriptors
The number of reserved file descriptors starts out at the lesser of 100 or 25% of the maximum. Squid refuses new client connections if the number of available (free) descriptors reaches this limit. It is increased if Squid encounters an error while trying to create a new TCP socket. In this case, you'll see a message in cache.log:
Reserved FD adjusted from 100 to 150 due to failures
Store Disk files open
This counter shows the number of disk files currently open for reading or writing. It is always zero if you are using the diskd storage scheme because disk files are opened by the diskd processes, rather than Squid itself. If you use the max_open_disk_fds directive in squid.conf, Squid stops opening more cache files for reading or writing when it reaches that limit. If your filesystem is a bottleneck, this is a simple way to sacrifice a few cache hits for stable performance.
The Internal Data Structures section gives a quick overview of how many objects are in the cache and how many are on disk or in memory. You can find more detail about Squid's data structure allocations in the mem page (see Section 14.2.1.2). This section has a few stats:
Internal Data Structures:
2873586 StoreEntries
1336 StoreEntries with MemObjects
1302 Hot Object Cache Items
2873375 on-disk objects
StoreEntries
This represents the number of objects cached by Squid. Each object in the cache uses one StoreEntry structure.
StoreEntries with MemObjects
MemObject is the data structure used for objects currently being requested and for objects stored in the memory cache.
Hot Object Cache Items
The Hot Object Cache is another name for the memory cache (see Appendix B). These objects are stored entirely in memory (as well as on disk). This number should always be less than the number of entries with MemObjects.
on-disk objects
This counter shows how many objects are currently stored on disk. The counter is incremented when the entire object has been successfully written. Thus, this number isn't necessarily equal to the number of StoreEntries minus the number of Hot Objects.
filedescriptors: Process File Descriptor Allocation
This page displays a table of all file descriptors currently opened by Squid. It looks like this:
File Type Tout Nread * Nwrite * Remote Address Description
---- ------ ---- -------- -------- ----------------- ------------------------------
3 File 0 0 0 /usr/local/squid/logs/cache.log
6 File 0 0 2083739 /usr/local/squid/logs/access.log
12 Pipe 0 0 0 unlinkd -> squid
13 File 0 0 2485913 /usr/local/squid/logs/store.log
15 Pipe 0 0 0 squid -> unlinkd
16 Socket 24 220853* 1924 65.200.216.110.80 http://downloads.mp3.com/
18 Pipe 0 0 0 squid -> diskd
19 Socket 179 476* 1747 202.59.16.30.4171 http://ads.vesperexchange.com/
21 Pipe 0 0 0 squid -> diskd
22 Socket 20 158783* 998 210.222.20.8.80 http://home.hanmir.com/a
24 Pipe 0 0 0 squid -> diskd
25 Socket 1 0 0* 210.222.20.8.80 http://home.hanmir.com/b
26 Socket 0 9048307* 1578290 .0 DNS Socket
27 Pipe 0 0 0 squid -> diskd
28 Socket 0 0 0* 66.28.234.77.80 http://updates.hotbar.com/
29 Socket 0 0* 0 .0 HTTP Socket
30 Pipe 0 0 0 squid -> diskd
31 Socket 0 93 1126 127.0.0.1.3434 ncsa_auth