Re: Cache Digests

From: Alex Rousskov <>
Date: Tue, 6 Oct 1998 11:47:36 -0600 (MDT)

On Tue, 6 Oct 1998, Niall Doherty wrote:

> What does the util: 318% on the entries line mean ?
> (The count is low coz the peer cache is only filling up now
> after upgrade to 2.0).
> What does the capacity signify ?

There are two kinds of "utilization" lines.

1) Entries: Suppose your cache has 1000 objects (entries: count). When
building a local (store) digest, Squid guessed that allocating space for 500
cache objects would be enough (entries: capacity). "Entries: utilization"
shows 200%. That's OK if "bits: utilization" is normal, see below.

2) Bits: For each entry in "entries: capacity" Squid allocates bits_per_entry
bits in the digest (bits: capacity). When digesting entries, some bits are
turned on (bits: on). Ideally, the bits utilization (bits on/bits capacity)
should be close to 50%. Looking at your stats, Squid guessed the capacity
just right!

> What about the bit and bit-seq lines ?

"bit:" see (2) above.

"bit-seq" is "bit sequence", i.e. an uninterrupted sequence of bits with the
same value ('0' or '1'). This line gives some insight on the quality of the
digest hashing function. Extreme values (e.g. very long average sequence
length) may indicate a problem even if bit utilization is 50%.
> digest: size: 55324 bytes
> entries: count: 281373 capacity: 88517 util: 318%
> deletion attempts: 0
> bits: per entry: 5 on: 216176 capacity: 442592 util: 49%
> bit-seq: count: 221121 avg.len: 2.00

Received on Tue Oct 06 1998 - 10:49:24 MDT

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