Split records across many subtables for better distribution across TMMs

Problem this snippet solves:

This iRule demonstrates how to use multiple subtables to distribute session table entries. As a subtable is pinned to a specific TMM, using multiple subtables distributes the load more evenly across TMMs. We use CRC32 hashing of the key being stored to deterministically pick the subtable name to store a key in.

Code :

when RULE_INIT {

       # Number of subtables to create (should be ~3+ x TMM count).  Use 100 as a test.
       set static::subtable_count 100

       # Time to save subtable entries for
       set static::lifetime 3600

       # Prefix to keep these subtable names unique from other iRules
       set static::prefix "mysubs"
}
when CLIENT_ACCEPTED {

       # Pick some unique key for the subtable entries
       set key [TCP::client_port]

       # Look up the key in the subtable this key should be crc32 hashed to and save the value
       set value [table lookup -subtable "${static::prefix}_[expr {[crc32 $key] % $static::subtable_count}]" $key]

       log local0. "Looked up $key in ${static::prefix}_[expr {[crc32 $key] % $static::subtable_count}] subtable and found \"$value\""

       # Check if there was a value for the given key
       if {$value eq ""}{

              # No value so add the key and value to the subtable determined by the crc32 hash of the key
              table set -subtable "${static::prefix}_[expr {[crc32 $key] % $static::subtable_count}]" $key "some value" indef $static::lifetime

       } else {
              # Do something with the stored value for this key
       }
}