Alert: hashPct num < 25

What does it mean? What do I do about it?

Example alert from the ProTop Portal:

What is the -hash primary broker parameter?

The -hash parameter specifies the size of the database buffer hash table (BHT).  The BHT is used to find blocks in the buffer pool.  The value of -hash should always be a prime number, to ensure more even distribution of entries in the hash table.

By default, the value of -hash is chosen at database startup by the primary broker, based on the size of the buffer pool.  It is set to a value that is a prime number larger than one-quarter the size of the buffer pool.  The value isn’t necessarily the next prime greater than (-B + -B2) / 4.  The broker picks an appropriate value from a hard-coded table of primes.  DBAs should not set -hash manually.  Let the broker choose the value.

What is the hashPct metric?

As a sanity check on -hash, ProTop calculates the ratio of -hash to the size of the buffer pool (-B + -B2).  Since the broker will always calculate a -hash value that is greater than 25% of the buffer pool size, we set an alert for hashPct values less than 25.

What to do when you see this alert?

Validate the ratio yourself: calculate ( (-hash) / ( -B + -B2 ) ) * 100.  If it is less than 25, then -hash has been set manually, to an improper value.  Check your database broker configuration (e.g. .pf file, script, conmgr.properties. etc.) and remove the manually set value of -hash, to allow the primary database broker to specify the value of -hash.  Note that a database restart is required to change the value of -hash.

If all else fails...

Contact us at support@wss.com or use the online chat. We'll be happy to help.