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Created April 21, 2015 06:35
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pgpool-memory cache debug.
# ----------------------------
# pgPool-II configuration file
# ----------------------------
#
# This file consists of lines of the form:
#
# name = value
#
# Whitespace may be used. Comments are introduced with "#" anywhere on a line.
# The complete list of parameter names and allowed values can be found in the
# pgPool-II documentation.
#
# This file is read on server startup and when the server receives a SIGHUP
# signal. If you edit the file on a running system, you have to SIGHUP the
# server for the changes to take effect, or use "pgpool reload". Some
# parameters, which are marked below, require a server shutdown and restart to
# take effect.
#
#------------------------------------------------------------------------------
# CONNECTIONS
#------------------------------------------------------------------------------
# - pgpool Connection Settings -
listen_addresses = 'localhost'
# Host name or IP address to listen on:
# '*' for all, '' for no TCP/IP connections
# (change requires restart)
port = 9999
# Port number
# (change requires restart)
socket_dir = '/var/run/pgpool'
# Unix domain socket path
# The Debian package defaults to
# /var/run/postgresql
# (change requires restart)
listen_backlog_multiplier = 2
# Set the backlog parameter of listen(2) to
# num_init_children * listen_backlog_multiplier.
# (change requires restart)
# - pgpool Communication Manager Connection Settings -
pcp_listen_addresses = 'localhost'
# Host name or IP address for pcp process to listen on:
# '*' for all, '' for no TCP/IP connections
# (change requires restart)
pcp_port = 9898
# Port number for pcp
# (change requires restart)
pcp_socket_dir = '/var/run/pgpool'
# Unix domain socket path for pcp
# The Debian package defaults to
# /var/run/postgresql
# (change requires restart)
# - Backend Connection Settings -
backend_hostname0 = '127.0.0.1'
# Host name or IP address to connect to for backend 0
backend_port0 = 5432
# Port number for backend 0
backend_weight0 = 1
# Weight for backend 0 (only in load balancing mode)
backend_data_directory0 = '/tmp/pgpool'
# Data directory for backend 0
# backend_flag0 = 'ALLOW_TO_FAILOVER'
# Controls various backend behavior
# ALLOW_TO_FAILOVER or DISALLOW_TO_FAILOVER
#backend_hostname1 = 'host2'
#backend_port1 = 5433
#backend_weight1 = 1
#backend_data_directory1 = '/data1'
#backend_flag1 = 'ALLOW_TO_FAILOVER'
# - Authentication -
enable_pool_hba = off
# Use pool_hba.conf for client authentication
pool_passwd = ''
# File name of pool_passwd for md5 authentication.
# "" disables pool_passwd.
# (change requires restart)
authentication_timeout = 60
# Delay in seconds to complete client authentication
# 0 means no timeout.
# - SSL Connections -
ssl = off
# Enable SSL support
# (change requires restart)
#ssl_key = './server.key'
# Path to the SSL private key file
# (change requires restart)
#ssl_cert = './server.cert'
# Path to the SSL public certificate file
# (change requires restart)
#ssl_ca_cert = ''
# Path to a single PEM format file
# containing CA root certificate(s)
# (change requires restart)
#ssl_ca_cert_dir = ''
# Directory containing CA root certificate(s)
# (change requires restart)
#------------------------------------------------------------------------------
# POOLS
#------------------------------------------------------------------------------
# - Pool size -
num_init_children = 40
# Number of pools
# (change requires restart)
max_pool = 2
# Number of connections per pool
# (change requires restart)
# - Life time -
child_life_time = 300
# Pool exits after being idle for this many seconds
child_max_connections = 200
# Pool exits after receiving that many connections
# 0 means no exit
connection_life_time = 300
# Connection to backend closes after being idle for this many seconds
# 0 means no close
client_idle_limit = 0
# Client is disconnected after being idle for that many seconds
# (even inside an explicit transactions!)
# 0 means no disconnection
#------------------------------------------------------------------------------
# LOGS
#------------------------------------------------------------------------------
# - Where to log -
log_destination = 'syslog'
# Where to log
# Valid values are combinations of stderr,
# and syslog. Default to stderr.
# - What to log -
log_line_prefix = '%t: pid %p: ' # printf-style string to output at beginning of each log line.
log_connections = on
# Log connections
log_hostname = on
# Hostname will be shown in ps status
# and in logs if connections are logged
log_statement = on
# Log all statements
log_per_node_statement = on
# Log all statements
# with node and backend informations
log_standby_delay = 'none'
# Log standby delay
# Valid values are combinations of always,
# if_over_threshold, none
# - Syslog specific -
syslog_facility = 'LOCAL1'
# Syslog local facility. Default to LOCAL0
syslog_ident = 'pgpool-dbcfg'
# Syslog program identification string
# Default to 'pgpool'
# - Debug -
debug_level = 0
# Debug message verbosity level
# 0 means no message, 1 or more mean verbose
#log_error_verbosity = default # terse, default, or verbose messages
#client_min_messages = notice # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# log
# notice
# warning
# error
#log_min_messages = warning # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# info
# notice
# warning
# error
# log
# fatal
# panic
#------------------------------------------------------------------------------
# FILE LOCATIONS
#------------------------------------------------------------------------------
pid_file_name = '/var/run/pgpool/pgpool.pid'
# PID file name
# (change requires restart)
logdir = '/var/log/pgpool'
# Directory of pgPool status file
# (change requires restart)
#------------------------------------------------------------------------------
# CONNECTION POOLING
#------------------------------------------------------------------------------
connection_cache = on
# Activate connection pools
# (change requires restart)
# Semicolon separated list of queries
# to be issued at the end of a session
# The default is for 8.3 and later
reset_query_list = 'ABORT; DISCARD ALL'
# The following one is for 8.2 and before
#reset_query_list = 'ABORT; RESET ALL; SET SESSION AUTHORIZATION DEFAULT'
#------------------------------------------------------------------------------
# REPLICATION MODE
#------------------------------------------------------------------------------
replication_mode = off
# Activate replication mode
# (change requires restart)
replicate_select = off
# Replicate SELECT statements
# when in replication mode
# replicate_select is higher priority than
# load_balance_mode.
insert_lock = on
# Automatically locks a dummy row or a table
# with INSERT statements to keep SERIAL data
# consistency
# Without SERIAL, no lock will be issued
lobj_lock_table = ''
# When rewriting lo_creat command in
# replication mode, specify table name to
# lock
# - Degenerate handling -
replication_stop_on_mismatch = off
# On disagreement with the packet kind
# sent from backend, degenerate the node
# which is most likely "minority"
# If off, just force to exit this session
failover_if_affected_tuples_mismatch = off
# On disagreement with the number of affected
# tuples in UPDATE/DELETE queries, then
# degenerate the node which is most likely
# "minority".
# If off, just abort the transaction to
# keep the consistency
#------------------------------------------------------------------------------
# LOAD BALANCING MODE
#------------------------------------------------------------------------------
load_balance_mode = off
# Activate load balancing mode
# (change requires restart)
ignore_leading_white_space = on
# Ignore leading white spaces of each query
white_function_list = ''
# Comma separated list of function names
# that don't write to database
# Regexp are accepted
black_function_list = 'nextval,setval,nextval,setval'
# Comma separated list of function names
# that write to database
# Regexp are accepted
database_redirect_preference_list = ''
# comma separated list of pairs of database and node id.
# example: postgres:primary,mydb[0-4]:1,mydb[5-9]:2'
# valid for streaming replicaton mode only.
app_name_redirect_preference_list = ''
# comma separated list of pairs of app name and node id.
# example: 'psql:primary,myapp[0-4]:1,myapp[5-9]:standby'
# valid for streaming replicaton mode only.
allow_sql_comments = off
# if on, ignore SQL comments when judging if load balance or
# query cache is possible.
# If off, SQL comments effectively prevent the judgment
# (pre 3.4 behavior).
#------------------------------------------------------------------------------
# MASTER/SLAVE MODE
#------------------------------------------------------------------------------
master_slave_mode = off
# Activate master/slave mode
# (change requires restart)
master_slave_sub_mode = 'slony'
# Master/slave sub mode
# Valid values are combinations slony or
# stream. Default is slony.
# (change requires restart)
# - Streaming -
sr_check_period = 0
# Streaming replication check period
# Disabled (0) by default
sr_check_user = 'nobody'
# Streaming replication check user
# This is necessary even if you disable
# streaming replication delay check with
# sr_check_period = 0
sr_check_password = ''
# Password for streaming replication check user
delay_threshold = 0
# Threshold before not dispatching query to standby node
# Unit is in bytes
# Disabled (0) by default
# - Special commands -
follow_master_command = ''
# Executes this command after master failover
# Special values:
# %d = node id
# %h = host name
# %p = port number
# %D = database cluster path
# %m = new master node id
# %H = hostname of the new master node
# %M = old master node id
# %P = old primary node id
# %r = new master port number
# %R = new master database cluster path
# %% = '%' character
#------------------------------------------------------------------------------
# HEALTH CHECK
#------------------------------------------------------------------------------
health_check_period = 0
# Health check period
# Disabled (0) by default
health_check_timeout = 20
# Health check timeout
# 0 means no timeout
health_check_user = 'nobody'
# Health check user
health_check_password = ''
# Password for health check user
health_check_max_retries = 0
# Maximum number of times to retry a failed health check before giving up.
health_check_retry_delay = 1
# Amount of time to wait (in seconds) between retries.
connect_timeout = 10000
# Timeout value in milliseconds before giving up to connect to backend.
# Default is 10000 ms (10 second). Flaky network user may want to increase
# the value. 0 means no timeout.
# Note that this value is not only used for health check,
# but also for ordinary conection to backend.
#------------------------------------------------------------------------------
# FAILOVER AND FAILBACK
#------------------------------------------------------------------------------
failover_command = ''
# Executes this command at failover
# Special values:
# %d = node id
# %h = host name
# %p = port number
# %D = database cluster path
# %m = new master node id
# %H = hostname of the new master node
# %M = old master node id
# %P = old primary node id
# %r = new master port number
# %R = new master database cluster path
# %% = '%' character
failback_command = ''
# Executes this command at failback.
# Special values:
# %d = node id
# %h = host name
# %p = port number
# %D = database cluster path
# %m = new master node id
# %H = hostname of the new master node
# %M = old master node id
# %P = old primary node id
# %r = new master port number
# %R = new master database cluster path
# %% = '%' character
fail_over_on_backend_error = off
# Initiates failover when reading/writing to the
# backend communication socket fails
# If set to off, pgpool will report an
# error and disconnect the session.
search_primary_node_timeout = 10
# Timeout in seconds to search for the
# primary node when a failover occurs.
# 0 means no timeout, keep searching
# for a primary node forever.
#------------------------------------------------------------------------------
# ONLINE RECOVERY
#------------------------------------------------------------------------------
recovery_user = 'nobody'
# Online recovery user
recovery_password = ''
# Online recovery password
recovery_1st_stage_command = ''
# Executes a command in first stage
recovery_2nd_stage_command = ''
# Executes a command in second stage
recovery_timeout = 90
# Timeout in seconds to wait for the
# recovering node's postmaster to start up
# 0 means no wait
client_idle_limit_in_recovery = 0
# Client is disconnected after being idle
# for that many seconds in the second stage
# of online recovery
# 0 means no disconnection
# -1 means immediate disconnection
#------------------------------------------------------------------------------
# WATCHDOG
#------------------------------------------------------------------------------
# - Enabling -
use_watchdog = off
# Activates watchdog
# (change requires restart)
# -Connection to up stream servers -
trusted_servers = ''
# trusted server list which are used
# to confirm network connection
# (hostA,hostB,hostC,...)
# (change requires restart)
ping_path = '/bin'
# ping command path
# (change requires restart)
# - Watchdog communication Settings -
wd_hostname = ''
# Host name or IP address of this watchdog
# (change requires restart)
wd_port = 9000
# port number for watchdog service
# (change requires restart)
wd_authkey = ''
# Authentication key for watchdog communication
# (change requires restart)
# - Virtual IP control Setting -
delegate_IP = ''
# delegate IP address
# If this is empty, virtual IP never bring up.
# (change requires restart)
ifconfig_path = '/sbin'
# ifconfig command path
# (change requires restart)
if_up_cmd = 'ifconfig eth0:0 inet $_IP_$ netmask 255.255.255.0'
# startup delegate IP command
# (change requires restart)
if_down_cmd = 'ifconfig eth0:0 down'
# shutdown delegate IP command
# (change requires restart)
arping_path = '/usr/sbin' # arping command path
# (change requires restart)
arping_cmd = 'arping -U $_IP_$ -w 1'
# arping command
# (change requires restart)
# - Behaivor on escalation Setting -
clear_memqcache_on_escalation = on
# Clear all the query cache on shared memory
# when standby pgpool escalate to active pgpool
# (= virtual IP holder).
# This should be off if client connects to pgpool
# not using virtual IP.
# (change requires restart)
wd_escalation_command = ''
# Executes this command at escalation on new active pgpool.
# (change requires restart)
# - Lifecheck Setting -
# -- common --
wd_lifecheck_method = 'heartbeat'
# Method of watchdog lifecheck ('heartbeat' or 'query')
# (change requires restart)
wd_interval = 10
# lifecheck interval (sec) > 0
# (change requires restart)
# -- heartbeat mode --
wd_heartbeat_port = 9694
# Port number for receiving heartbeat signal
# (change requires restart)
wd_heartbeat_keepalive = 2
# Interval time of sending heartbeat signal (sec)
# (change requires restart)
wd_heartbeat_deadtime = 30
# Deadtime interval for heartbeat signal (sec)
# (change requires restart)
heartbeat_destination0 = 'host0_ip1'
# Host name or IP address of destination 0
# for sending heartbeat signal.
# (change requires restart)
heartbeat_destination_port0 = 9694
# Port number of destination 0 for sending
# heartbeat signal. Usually this is the
# same as wd_heartbeat_port.
# (change requires restart)
heartbeat_device0 = ''
# Name of NIC device (such like 'eth0')
# used for sending/receiving heartbeat
# signal to/from destination 0.
# This works only when this is not empty
# and pgpool has root privilege.
# (change requires restart)
#heartbeat_destination1 = 'host0_ip2'
#heartbeat_destination_port1 = 9694
#heartbeat_device1 = ''
# -- query mode --
wd_life_point = 3
# lifecheck retry times
# (change requires restart)
wd_lifecheck_query = 'SELECT 1'
# lifecheck query to pgpool from watchdog
# (change requires restart)
wd_lifecheck_dbname = 'template1'
# Database name connected for lifecheck
# (change requires restart)
wd_lifecheck_user = 'nobody'
# watchdog user monitoring pgpools in lifecheck
# (change requires restart)
wd_lifecheck_password = ''
# Password for watchdog user in lifecheck
# (change requires restart)
# - Other pgpool Connection Settings -
#other_pgpool_hostname0 = 'host0'
# Host name or IP address to connect to for other pgpool 0
# (change requires restart)
#other_pgpool_port0 = 5432
# Port number for othet pgpool 0
# (change requires restart)
#other_wd_port0 = 9000
# Port number for othet watchdog 0
# (change requires restart)
#other_pgpool_hostname1 = 'host1'
#other_pgpool_port1 = 5432
#other_wd_port1 = 9000
#------------------------------------------------------------------------------
# OTHERS
#------------------------------------------------------------------------------
relcache_expire = 0
# Life time of relation cache in seconds.
# 0 means no cache expiration(the default).
# The relation cache is used for cache the
# query result against PostgreSQL system
# catalog to obtain various information
# including table structures or if it's a
# temporary table or not. The cache is
# maintained in a pgpool child local memory
# and being kept as long as it survives.
# If someone modify the table by using
# ALTER TABLE or some such, the relcache is
# not consistent anymore.
# For this purpose, cache_expiration
# controls the life time of the cache.
relcache_size = 256
# Number of relation cache
# entry. If you see frequently:
# "pool_search_relcache: cache replacement happend"
# in the pgpool log, you might want to increate this number.
check_temp_table = on
# If on, enable temporary table check in SELECT statements.
# This initiates queries against system catalog of primary/master
# thus increases load of master.
# If you are absolutely sure that your system never uses temporary tables
# and you want to save access to primary/master, you could turn this off.
# Default is on.
check_unlogged_table = on
# If on, enable unlogged table check in SELECT statements.
# This initiates queries against system catalog of primary/master
# thus increases load of master.
# If you are absolutely sure that your system never uses unlogged tables
# and you want to save access to primary/master, you could turn this off.
# Default is on.
#------------------------------------------------------------------------------
# IN MEMORY QUERY MEMORY CACHE
#------------------------------------------------------------------------------
memory_cache_enabled = on
# If on, use the memory cache functionality, off by default
memqcache_method = 'memcached'
# Cache storage method. either 'shmem'(shared memory) or
# 'memcached'. 'shmem' by default
# (change requires restart)
memqcache_memcached_host = '127.0.0.1'
# Memcached host name or IP address. Mandatory if
# memqcache_method = 'memcached'.
# Defaults to localhost.
# (change requires restart)
memqcache_memcached_port = 11211
# Memcached port number. Mondatory if memqcache_method = 'memcached'.
# Defaults to 11211.
# (change requires restart)
memqcache_total_size = 67108864
# Total memory size in bytes for storing memory cache.
# Mandatory if memqcache_method = 'shmem'.
# Defaults to 64MB.
# (change requires restart)
memqcache_max_num_cache = 1000000
# Total number of cache entries. Mandatory
# if memqcache_method = 'shmem'.
# Each cache entry consumes 48 bytes on shared memory.
# Defaults to 1,000,000(45.8MB).
# (change requires restart)
memqcache_expire = 0
# Memory cache entry life time specified in seconds.
# 0 means infinite life time. 0 by default.
# (change requires restart)
memqcache_auto_cache_invalidation = on
# If on, invalidation of query cache is triggered by corresponding
# DDL/DML/DCL(and memqcache_expire). If off, it is only triggered
# by memqcache_expire. on by default.
# (change requires restart)
memqcache_maxcache = 409600
# Maximum SELECT result size in bytes.
# Must be smaller than memqcache_cache_block_size. Defaults to 400KB.
# (change requires restart)
memqcache_cache_block_size = 1048576
# Cache block size in bytes. Mandatory if memqcache_method = 'shmem'.
# Defaults to 1MB.
# (change requires restart)
memqcache_oiddir = '/var/log/pgpool/oiddir'
# Temporary work directory to record table oids
# (change requires restart)
white_memqcache_table_list = ''
# Comma separated list of table names to memcache
# that don't write to database
# Regexp are accepted
black_memqcache_table_list = ''
# Comma separated list of table names not to memcache
# that don't write to database
# Regexp are accepted
sudo ./pgpool -n -f ~/pgpool/pgpool.conf
2015-04-21 06:29:02: pid 1105: LOG: Setting up socket for ::1:9999
2015-04-21 06:29:02: pid 1105: LOG: Setting up socket for 127.0.0.1:9999
2015-04-21 06:29:02: pid 1105: LOG: pgpool-II successfully started. version 3.4.2 (tataraboshi)
2015-04-21 06:29:09: pid 1145: LOG: new connection received
2015-04-21 06:29:09: pid 1145: DETAIL: connecting host=localhost port=41176
2015-04-21 06:29:11: pid 1143: LOG: new connection received
2015-04-21 06:29:11: pid 1143: DETAIL: connecting host=localhost port=41178
2015-04-21 06:29:14: pid 1143: LOG: statement: select comments from users where id=1;
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_catalog.pg_class AS c, pg_attribute AS a WHERE c.relname = 'pg_class' AND a.attrelid = c.oid AND a.attname = 'relistemp'
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_class AS c, pg_namespace AS n WHERE c.relname = 'users' AND c.relnamespace = n.oid AND n.nspname ~ '^pg_temp_'
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.relname = 'pg_namespace'
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) from (SELECT has_function_privilege('ruser', 'to_regclass(cstring)', 'execute') WHERE EXISTS(SELECT * FROM pg_catalog.pg_proc AS p WHERE p.proname = 'to_regclass')) AS s
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_class AS c, pg_namespace AS n WHERE c.oid = to_regclass('users') AND c.relnamespace = n.oid AND n.nspname = 'pg_catalog'
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.oid = to_regclass('users') AND (c.relkind = 'v' OR c.relkind = 'm')
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_catalog.pg_class AS c, pg_catalog.pg_attribute AS a WHERE c.relname = 'pg_class' AND a.attrelid = c.oid AND a.attname = 'relpersistence'
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.oid = to_regclass('users') AND c.relpersistence = 'u'
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: select comments from users where id=1;
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT COALESCE(to_regclass('users')::oid, 0)
2015-04-21 06:29:14: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: SELECT oid FROM pg_database WHERE datname = 'mydb'
2015-04-21 06:29:16: pid 1143: LOG: statement: select comments from users where id=1;
2015-04-21 06:29:16: pid 1143: LOG: fetch from memory cache
2015-04-21 06:29:16: pid 1143: DETAIL: query result fetched from cache. statement: select comments from users where id=1;
2015-04-21 06:29:32: pid 1143: LOG: statement: update users set comments='hello' where id=1;
2015-04-21 06:29:32: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: update users set comments='hello' where id=1;
2015-04-21 06:29:33: pid 1143: LOG: statement: select comments from users where id=1;
2015-04-21 06:29:33: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: select comments from users where id=1;
2015-04-21 06:29:39: pid 1143: LOG: statement: update users set comments='hello world' where id=1;
2015-04-21 06:29:39: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: update users set comments='hello world' where id=1;
2015-04-21 06:29:40: pid 1143: LOG: statement: select comments from users where id=1;
2015-04-21 06:29:40: pid 1143: LOG: fetch from memory cache
2015-04-21 06:29:40: pid 1143: DETAIL: query result fetched from cache. statement: select comments from users where id=1;
2015-04-21 06:29:43: pid 1143: LOG: statement: select comments from users where id=1;
2015-04-21 06:29:43: pid 1143: LOG: fetch from memory cache
2015-04-21 06:29:43: pid 1143: DETAIL: query result fetched from cache. statement: select comments from users where id=1;
2015-04-21 06:29:51: pid 1143: LOG: statement: update users set comments='boooo' where id=1;
2015-04-21 06:29:51: pid 1143: LOG: DB node id: 0 backend pid: 1249 statement: update users set comments='boooo' where id=1;
2015-04-21 06:29:52: pid 1143: LOG: statement: select comments from users where id=1;
2015-04-21 06:29:52: pid 1143: LOG: fetch from memory cache
2015-04-21 06:29:52: pid 1143: DETAIL: query result fetched from cache. statement: select comments from users where id=1;
psql -U ruser -d mydb -h 127.0.0.1 -p 9999
Password for user ruser:
psql (9.4.1)
Type "help" for help.
mydb=> select comments from users where id=1;
comments
----------
boooo
(1 row)
mydb=> select comments from users where id=1;
comments
----------
boooo
(1 row)
mydb=> update users set comments='hello' where id=1;
UPDATE 1
mydb=> select comments from users where id=1;
comments
----------
hello
(1 row)
mydb=> update users set comments='hello world' where id=1;
UPDATE 1
mydb=> select comments from users where id=1;
comments
----------
hello
(1 row)
mydb=> update users set comments='booo' where id=1;
UPDATE 1
mydb=> select comments from users where id=1;
comments
----------
hello
(1 row)
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