Examining Thread Information - Oracle 5.0 Reference Manual

The server uses the host cache for several purposes:
• By caching the results of IP-to-host name lookups, the server avoids doing a DNS lookup for each
client connection. Instead, for a given host, it needs to perform a lookup only for the first connection
from that host.
• The cache contains information about errors that occur during the connection process. Some
errors are considered "blocking." If too many of these occur successively from a given host
without a successful connection, the server blocks further connections from that host. The
max_connect_errors
blocking occurs. See
To unblock blocked hosts, flush the host cache by issuing a
mysqladmin flush-hosts
It is possible for a blocked host to become unblocked even without
hosts has occurred since the last connection attempt from the blocked host. This can occur because
the server discards the least recently used cache entry to make room for a new entry if the cache is full
when a connection arrives from a client IP not in the cache. If the discarded entry is for a blocked host,
that host becomes unblocked.
The host cache is enabled by default. To disable it, start the server with the
[420]
cache
To disable DNS host name lookups, start the server with the
this case, the server uses only IP addresses and not host names to match connecting hosts to rows in
the MySQL grant tables. Only accounts specified in those tables using IP addresses can be used.
If you have a very slow DNS and many hosts, you might be able to improve performance either by
disabling DNS lookups with
define (default value: 128) and recompiling the server
To disallow TCP/IP connections entirely, start the server with the
Some connection errors are not associated with TCP connections, occur very early in the connection
process (even before an IP address is known), or are not specific to any particular IP address (such as
out-of-memory conditions).

8.10. Examining Thread Information

When you are attempting to ascertain what your MySQL server is doing, it can be helpful to examine
the process list, which is the set of threads currently executing within the server. Process list
information is available from these sources:
• The
SHOW [FULL] PROCESSLIST
• The
SHOW PROFILE
• The
mysqladmin processlist
Administering a MySQL Server"
You can always view information about your own threads. To view information about threads being
executed for other accounts, you must have the
Each process list entry contains several pieces of information:
• is the connection identifier for the client associated with the thread.
Id
• and
User
• is the default database for the thread, or
db
Examining Thread Information
[467] system variable determines the number of permitted errors before
Section C.5.2.6,
command.
option.
--skip-name-resolve
statement: Section 13.7.5.29,
indicate the account associated with the thread.
Host
"Host 'host_name' is
[420]
statement: Section 13.7.5.27,
"SHOW PROFILES
command: Section 4.5.2,
[577]
PROCESS
if none is selected.
NULL
731
blocked".
statement or executing a
FLUSH HOSTS
FLUSH HOSTS
--skip-host-
--skip-name-resolve
or by increasing the
HOST_CACHE_SIZE
--skip-networking
"SHOW PROCESSLIST
Syntax"
"mysqladmin — Client for
privilege.
if activity from other
[420] option. In
[421] option.
Syntax"