| Index | Alphabetical Index |
Option Name: | shared_transient_entries_limit |
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Replaces: | collapsed_forwarding_shared_entries_limit |
Requires: | |
Default Value: | shared_transient_entries_limit 16384 |
Suggested Config: |
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This directive limits the size of a table used for sharing current transaction information among SMP workers. A table entry stores meta information about a single cache entry being delivered to Squid client(s) by one or more SMP workers. A single table entry consumes less than 128 shared memory bytes. The limit should be significantly larger than the number of concurrent non-collapsed cachable responses leaving Squid. For a cache that handles less than 5000 concurrent requests, the default setting of 16384 should be plenty. Using excessively large values wastes shared memory. Limiting the table size too much results in hash collisions, leading to lower hit ratio and missed SMP request collapsing opportunities: Transactions left without a table entry cannot cache their responses and are invisible to other concurrent requests for the same resource. A zero limit is allowed but unsupported. A positive small limit lowers hit ratio, but zero limit disables a lot of essential synchronization among SMP workers, leading to HTTP violations (e.g., stale hit responses). It also disables shared collapsed forwarding: A worker becomes unable to collapse its requests on transactions in other workers, resulting in more trips to the origin server and more cache thrashing. |
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| Index | Alphabetical Index |