Postgres 9.3 read block error went into recovery mode

We recently experienced crash on out postgres production server. Here's our
server environment:

- Postgres 9.3
- in OpenVZ container
- total memory: 64GB

Here's the error snippet from postgres log:

ERROR: could not read block 356121 in file "base/33134/33598.2": Bad
address
LOG: server process (PID 21119) was terminated by signal 7: Bus error

WARNING: terminating connection because of crash of another server process
DETAIL: The postmaster has commanded this server process to roll back the
current transaction and exit, because another server process exited
abnormally
HINT: In a moment you should be able to reconnect to the database and
repeat your command.
LOG: all server processes terminated; reinitializing
LOG: database system was interrupted; last known up at 2013-12-03 08:47:06
UTC
LOG: database system was not properly shut down; automatic recovery in
progress
UTC FATAL: the database system is in recovery mode

LOG: checkpoint complete: wrote 10499 buffers (0.7%); 0 transaction log
file(s) added, 0 removed, 4 recycled; write=0.215 s, sync=11.405 s,
total=11.631
FATAL: the database system is in recovery mode
LOG: database system is ready to accept connections

Can anyone suggests whether this is critical error? Does it indicate any
data corruption in postgres?

Although we think this is unlikely related, but this is what we did few
hours before the crash:

(1) Try to improve query performance by tweaking this:
a) shared_buffer: 8GB -> 16GB
b) effective_cache_size: 16GB -> 32GB
c) random_page_cost: 4 -> 2
d) restart postgres

(2) Due to no obvious improvement in performace, change the setting in (1)
back to before & restart

Thanks if anyone has any insight.

regards,
shuwn yuan