9.2.3 upgrade reduced pgbench performance by 60%

Hi,

I recently upgraded PostgreSQL from 9.0.12 to 9.2.3 on a test server to compare performance. I'm using pgbench to measure which results in around a 60% reduction.

The non-default configuration remains identical between versions except archive_command (different location) and custom_variable_classes (no longer supported) and are detailed are below. Is there some updated default configuration that I'm missing? Perhaps it's because of the new cascading replication feature? I've tried tweaking the memory settings to no avail.

The Linux server is on a cloud and has 4GB RAM and 2 CPUs and the same server is running both master and slave (these are separate in production). If you'd like any more details please ask. Here are the pgbench results:

PostgreSQL 9.0.12
-----------------
/usr/pgsql-9.0/bin/pgbench -c 4 -t 20000 pgbench

starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
query mode: simple
number of clients: 4
number of threads: 1
number of transactions per client: 20000
number of transactions actually processed: 80000/80000
tps = 140.784635 (including connections establishing)
tps = 140.789389 (excluding connections establishing)

starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
query mode: simple
number of clients: 4
number of threads: 1
number of transactions per client: 20000
number of transactions actually processed: 80000/80000
tps = 142.027320 (including connections establishing)
tps = 142.032815 (excluding connections establishing)

starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
query mode: simple
number of clients: 4
number of threads: 1
number of transactions per client: 20000
number of transactions actually processed: 80000/80000
tps = 150.745875 (including connections establishing)
tps = 150.750959 (excluding connections establishing)

PostgreSQL 9.2.3
-----------------
/usr/pgsql-9.2/bin/pgbench -c 4 -t 20000 pgbench

starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
query mode: simple
number of clients: 4
number of threads: 1
number of transactions per client: 20000
number of transactions actually processed: 80000/80000
tps = 60.273767 (including connections establishing)
tps = 60.274429 (excluding connections establishing)

starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
query mode: simple
number of clients: 4
number of threads: 1
number of transactions per client: 20000
number of transactions actually processed: 80000/80000
tps = 57.634077 (including connections establishing)
tps = 57.634847 (excluding connections establishing)

starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
query mode: simple
number of clients: 4
number of threads: 1
number of transactions per client: 20000
number of transactions actually processed: 80000/80000
tps = 60.516492 (including connections establishing)
tps = 60.517250 (excluding connections establishing)

The non-default configuration items
-----------------
listen_addresses = '*' # what IP address(es) to listen on;
max_connections = 100 # (change requires restart)
shared_buffers = 256MB # min 128kB
temp_buffers = 128MB # min 800kB
work_mem = 32MB # min 64kB
maintenance_work_mem = 128MB # min 1MB
max_stack_depth = 8MB # min 100kB
wal_level = hot_standby # minimal, archive, or hot_standby
checkpoint_segments = 3 # in logfile segments, min 1, 16MB each
checkpoint_completion_target = 0.9 # checkpoint target duration, 0.0 - 1.0
archive_mode = on # allows archiving to be done
archive_command = 'cp -f %p /var/lib/pgsql/9.0/archive/%f </dev/null' # command to use to archive a logfile segment
max_wal_senders = 10 # max number of walsender processes
effective_cache_size = 1GB
default_statistics_target = 2000 # range 1-10000
log_destination = 'stderr' # Valid values are combinations of
logging_collector = on # Enable capturing of stderr and csvlog
log_directory = 'pg_log' # directory where log files are written,
log_filename = 'postgresql-%a.log' # log file name pattern,
log_truncate_on_rotation = on # If on, an existing log file of the
log_rotation_age = 1d # Automatic rotation of logfiles will
log_rotation_size = 0 # Automatic rotation of logfiles will
log_min_duration_statement = 5000 # -1 is disabled, 0 logs all statements
log_checkpoints = on
log_line_prefix = '%t:%r:%u(at)%d:[%p]: ' # special values:
log_statement = 'none' # none, ddl, mod, all
autovacuum = on # changed by pgb_test for pgbench testing
log_autovacuum_min_duration = 100 # -1 disables, 0 logs all actions and
datestyle = 'iso, mdy'
lc_messages = 'en_US.UTF-8' # locale for system error message
lc_monetary = 'en_US.UTF-8' # locale for monetary formatting
lc_numeric = 'en_US.UTF-8' # locale for number formatting
lc_time = 'en_US.UTF-8' # locale for time formatting
default_text_search_config = 'pg_catalog.english'
shared_preload_libraries = 'auto_explain'
custom_variable_classes = 'auto_explain'
auto_explain.log_min_duration = '15s'