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postgres -- the Postgres backend server
postgres [-B n_buffers]
[-D data_directory] [-E ] [-F ]
[-P filedes] [-Q ] [-S n_buffers ] [-e ]
[-d
debug_level] [-o output_file] [-s ] [dbname]
The Postgres
backend server can be executed directly from the user shell. This should
be done only while debugging by the DBA, and should not be done while
other Postgres backends are being managed by a postmaster on this set
of databases.
The optional argument dbname specifies the name of the database
to be accessed. Dbname defaults to the value of the USER
environment variable.
The postgres server understands the following command-line options:
- -D
data_directory
- This option specifies the pathname of the directory that
contains the database system data (the tables, the catalogs, etc.). If
you don't specify this option, Postgres uses the value of the PGDATA environment
variable. You must either specify a -D option or set PGDATA. The data
directory pathname for a database system is normally determined when the
database system is created with initdb, with a --pgdata option to initdb.
- -B n_buffers
- If the backend is running under the postmaster, n_buffers
is the number of shared-memory buffers that the postmaster has allocated
for the backend server processes that it starts. If the backend is running
standalone, this specifies the number of buffers to allocate. This value
defaults to 64, and each buffer is 8k bytes.
- -E
- Echo all queries.
- -F
- Disable
automatic fsync() call after each transaction. This option improves performance,
but an operating system crash while a transaction is in progress will
probably cause data loss.
- -P filedes
- filedes specifies the file descriptor
that corresponds to the socket (port) on which to communicate to the frontend
process. This option is not useful for interactive use.
- -Q
- Specifies `quiet'
mode.
- -S
- Specifies the amount of memory to be used by internal sorts before
using disk files for sorting. This value is specified in 1k bytes, and
defaults to 512.
- -e
- The -e option controls how dates are input to and output
from the database.
- If the
- -e option is supplied, then all dates passed
to and from the frontend processes will be assumed to be in European format
ie. DD-MM-YYYY otherwise dates are input and output in American format ie.
MM-DD-YYYY
- -d debug_level
- Turns on debugging at the numeric level debug_level.
Turning on debugging will cause query, parse trees, and query plans to
be displayed.
- -o output_file
- Sends all debugging and error output to output_file.
If the backend is running under the postmaster, error messages are still
sent to the frontend process as well as to output_file, but debugging
output is sent to the controlling tty of the postmaster (since only one
file descriptor can be sent to an actual file).
- -s
- Print time information
and other statistics at the end of each query. This is useful for benchmarking
or for use in tuning the number of buffers.
There are several other options that may be specified, used mainly for
debugging purposes. These are listed here only for the use by Postgres
system developers. Use of any of these options is highly discouraged. Furthermore,
any of these options may disappear or change at any time.
- -An|r|b|Qn |Xn
- This
option generates a tremendous amount of output.
- -L
- Turns off the locking
system.
- -N
- Disables use of newline as a query delimiter.
- -b
- Enables generation
of bushy query plan trees (as opposed to left-deep query plans trees).
These query plans are not intended for actual execution; in addition,
this flag often causes Postgres to run out of memory.
- -f
- Forbids the use
of particular scan and join methods: s and i disable sequential and index
scans respectively, while n, m and h disable nested-loop, merge and hash
joins respectively. This is another feature that may not necessarily produce
executable plans.
- -p
- Indicates to the backend server that it has been started
by a postmaster and make different assumptions about buffer pool management,
file descriptors, etc.
- -tpa[rser]|pl[anner]|e[xecutor]
- Print timing statistics
for each query relating to each of the major system modules. This option
cannot be used with -s.
ipcclean(1)
, psql(1)
, postmaster(1)
.
Of the nigh-infinite number of error messages you may see when
you execute the backend server directly, the most common will probably
be:
- semget: No space left on device
- If you see this message, you should
run the ipcclean command. After doing this, try starting postgres again.
If this still doesn't work, you probably need to configure your kernel
for shared memory and semaphores as described in the installation notes.
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