Commit Graph

320 Commits

Author SHA1 Message Date
Tom Lane 9daec77e16 Simplify correct use of simple_prompt().
The previous API for this function had it returning a malloc'd string.
That meant that callers had to check for NULL return, which few of them
were doing, and it also meant that callers had to remember to free()
the string later, which required extra logic in most cases.

Instead, make simple_prompt() write into a buffer supplied by the caller.
Anywhere that the maximum required input length is reasonably small,
which is almost all of the callers, we can just use a local or static
array as the buffer instead of dealing with malloc/free.

A fair number of callers used "pointer == NULL" as a proxy for "haven't
requested the password yet".  Maintaining the same behavior requires
adding a separate boolean flag for that, which adds back some of the
complexity we save by removing free()s.  Nonetheless, this nets out
at a small reduction in overall code size, and considerably less code
than we would have had if we'd added the missing NULL-return checks
everywhere they were needed.

In passing, clean up the API comment for simple_prompt() and get rid
of a very-unnecessary malloc/free in its Windows code path.

This is nominally a bug fix, but it does not seem worth back-patching,
because the actual risk of an OOM failure in any of these places seems
pretty tiny, and all of them are client-side not server-side anyway.

This patch is by me, but it owes a great deal to Michael Paquier
who identified the problem and drafted a patch for fixing it the
other way.

Discussion: <CAB7nPqRu07Ot6iht9i9KRfYLpDaF2ZuUv5y_+72uP23ZAGysRg@mail.gmail.com>
2016-08-30 17:02:02 -04:00
Tom Lane 37f6fd1eaa Fix initdb misbehavior when user mis-enters superuser password.
While testing simple_prompt() revisions, I happened to notice that
current initdb behaves rather badly when --pwprompt is specified and
the user miskeys the second password.  It complains about the mismatch,
does "rm -rf" on the data directory, and exits.  The problem is that
since commit c4a8812cf, there's a standalone backend sitting waiting
for commands at that point.  It gets unhappy about its datadir having
gone away, and spews a PANIC message at the user, which is not nice.
(And the shell then adds to the mess with meaningless bleating about a
core dump...)  We don't really want that sort of thing to happen unless
there's an internal failure in initdb, which this surely is not.

The best fix seems to be to move the collection of the password
earlier, so that it's done essentially as part of argument collection,
rather than at the rather ad-hoc time it was done before.

Back-patch to 9.6 where the problem was introduced.
2016-08-30 15:25:01 -04:00
Tom Lane a00c583147 Make initdb's suggested "pg_ctl start" command line more reliable.
The original coding here was not nearly careful enough about quoting
special characters, and it didn't get corner cases right for constructing
the pg_ctl path either.  Use join_path_components() and appendShellString()
to do it honestly, so that the string will more likely work if blindly
copied-and-pasted.

While at it, teach appendShellString() not to quote strings that clearly
don't need it, so that the output from initdb doesn't become uglier than
it was before in typical cases where quoting is not needed.

Ryan Murphy, reviewed by Michael Paquier and myself

Discussion: <CAHeEsBeAe1FeBypT3E8R1ZVZU0e8xv3A-7BHg6bEOi=jZny2Uw@mail.gmail.com>
2016-08-20 15:05:25 -04:00
Magnus Hagander 0921554657 Disable update_process_title by default on Windows
The performance overhead of this can be significant on Windows, and most
people don't have the tools to view it anyway as Windows does not have
native support for process titles.

Discussion: <0A3221C70F24FB45833433255569204D1F5BE3E8@G01JPEXMBYT05>

Takayuki Tsunakawa
2016-08-17 10:43:16 +02:00
Stephen Frost 47f5bb9f53 Correctly dump database and tablespace ACLs
Dump out the appropriate GRANT/REVOKE commands for databases and
tablespaces from pg_dumpall to replicate what the current state is.

This was broken during the changes to buildACLCommands for 9.6+
servers for pg_init_privs.
2016-07-17 09:04:46 -04:00
Tom Lane 16ea51a263 Pin the built-in index access methods.
This was overlooked in commit 473b93287, which introduced DROP ACCESS
METHOD.  Although that command is restricted to superusers, we don't want
even superusers dropping the built-in methods; "DROP ACCESS METHOD btree"
in particular is unrecoverable from.  Pin these objects in the same way
that other initdb-created objects are pinned.

I chose to bump catversion for this fix.  That's not absolutely necessary
perhaps, but it will ensure that no 9.6 production systems are missing
the pin entries.
2016-05-19 14:40:02 -04:00
Stephen Frost 6f69b96390 Wording quibbles regarding initdb username
Use disallowed instead of reserved, cannot instead of can not, and
double quotes instead of single quotes.

Also add a test to cover the bug which started this discussion.

Per discussion with Tom.
2016-05-08 12:58:21 -04:00
Stephen Frost 7df974ee0b Disallow superuser names starting with 'pg_' in initdb
As with CREATE ROLE, disallow users from specifying initial
superuser names which begin with 'pg_' in initdb.

Per discussion with Tom.
2016-05-08 11:55:44 -04:00
Tom Lane 34c33a1f00 Add BSD authentication method.
Create a "bsd" auth method that works the same as "password" so far as
clients are concerned, but calls the BSD Authentication service to
check the password.  This is currently only available on OpenBSD.

Marisa Emerson, reviewed by Thomas Munro
2016-04-08 13:52:06 -04:00
Stephen Frost 23f34fa4ba In pg_dump, include pg_catalog and extension ACLs, if changed
Now that all of the infrastructure exists, add in the ability to
dump out the ACLs of the objects inside of pg_catalog or the ACLs
for objects which are members of extensions, but only if they have
been changed from their original values.

The original values are tracked in pg_init_privs.  When pg_dump'ing
9.6-and-above databases, we will dump out the ACLs for all objects
in pg_catalog and the ACLs for all extension members, where the ACL
has been changed from the original value which was set during either
initdb or CREATE EXTENSION.

This should not change dumps against pre-9.6 databases.

Reviews by Alexander Korotkov, Jose Luis Tallon
2016-04-06 21:45:32 -04:00
Stephen Frost 6c268df127 Add new catalog called pg_init_privs
This new catalog holds the privileges which the system was
initialized with at initdb time, along with any permissions set
by extensions at CREATE EXTENSION time.  This allows pg_dump
(and any other similar use-cases) to detect when the privileges
set on initdb-created or extension-created objects have been
changed from what they were set to at initdb/extension-creation
time and handle those changes appropriately.

Reviews by Alexander Korotkov, Jose Luis Tallon
2016-04-06 21:45:32 -04:00
Tom Lane b41fb65056 Fix unobvious interaction between -X switch and subdirectory creation.
Turns out the only reason initdb -X worked is that pg_mkdir_p won't
whine if you point it at something that's a symlink to a directory.
Otherwise, the attempt to create pg_xlog/ just like all the other
subdirectories would have failed.  Let's be a little more explicit
about what's happening.  Oversight in my patch for bug #13853
(mea culpa for not testing -X ...)
2016-01-07 18:20:57 -05:00
Tom Lane 33b054bc79 Use plain mkdir() not pg_mkdir_p() to create subdirectories of PGDATA.
When we're creating subdirectories of PGDATA during initdb, we know darn
well that the parent directory exists (or should exist) and that the new
subdirectory doesn't (or shouldn't).  There is therefore no need to use
anything more complicated than mkdir().  Using pg_mkdir_p() just opens us
up to unexpected failure modes, such as the one exhibited in bug #13853
from Nuri Boardman.  It's not very clear why pg_mkdir_p() went wrong there,
but it is clear that we didn't need to be trying to create parent
directories in the first place.  We're not even saving any code, as proven
by the fact that this patch nets out at minus five lines.

Since this is a response to a field bug report, back-patch to all branches.
2016-01-07 15:22:24 -05:00
Tom Lane dad08994b2 In initdb's post-bootstrap phase, drop temp tables explicitly.
Although these temp tables will get removed from template1 at the end of
the standalone-backend run, that's too late to keep them from getting
copied into the template0 and postgres databases, now that we use only a
single backend run for the whole sequence.  While no real harm is done
by the extra copies (since they'd be deleted on first use of the temp
schema), it's still unsightly, and it would mean some wasted cycles for
every database creation for the life of the installation.

Oversight in commit c4a8812cf6.  Noticed by Amit Langote.
2016-01-06 12:25:32 -05:00
Bruce Momjian ee94300446 Update copyright for 2016
Backpatch certain files through 9.1
2016-01-02 13:33:40 -05:00
Tom Lane 01e386a325 Avoid VACUUM FULL altogether in initdb.
Commit ed7b3b3811 purported to remove initdb's use of VACUUM FULL,
as had been agreed to in a pghackers discussion back in Dec 2014.
But it missed this one ...
2015-12-23 20:09:01 -05:00
Tom Lane c4a8812cf6 Use just one standalone-backend session for initdb's post-bootstrap steps.
Previously, each subroutine in initdb fired up its own standalone backend
session.  Over time we'd grown as many as fifteen of these sessions,
and the cumulative startup and shutdown work for them was getting pretty
noticeable.  Combining things so that all these steps share a single
backend session cuts a good 10% off the total runtime of initdb, more
if you're not fsync'ing.

The main stumbling block to doing this before was that some of the sessions
were run with -j and some not.  The improved definition of -j mode
implemented by my previous commit makes it possible to fix that by running
all the post-bootstrap steps with -j; we just have to use double instead of
single newlines to end command strings.  (This is only absolutely necessary
around the VACUUM and CREATE DATABASE steps, since those can't be run in a
transaction block.  But it seems best to make them all use double newlines
so that the commands remain separate for error-reporting purposes.)

A minor disadvantage is that since initdb can't tell how much of its
output the backend has executed, we can no longer have the per-step
progress reporting initdb used to print.  But things are fast enough
nowadays that that's not really all that useful anyway.

In passing, add more const decoration to some of the static arrays in
initdb.c.
2015-12-17 19:38:21 -05:00
Tom Lane 1943c000b7 initdb -S should now have an explicit check that $PGDATA is valid.
The fsync code from the backend essentially assumes that somebody's already
validated PGDATA, at least to the extent of it being a readable directory.
That's safe enough for initdb's normal code path too, but "initdb -S"
doesn't have any other processing at all that touches the target directory.
To have reasonable error-case behavior, add a pg_check_dir call.
Per gripe from Peter E.
2015-05-29 17:02:58 -04:00
Tom Lane 57e1138bcc Remove special cases for ETXTBSY from new fsync'ing logic.
The argument that this is a sufficiently-expected case to be silently
ignored seems pretty thin.  Andres had brought it up back when we were
still considering that most fsync failures should be hard errors, and it
probably would be legit not to fail hard for ETXTBSY --- but the same is
true for EROFS and other cases, which is why we gave up on hard failures.
ETXTBSY is surely not a normal case, so logging the failure seems fine
from here.
2015-05-29 15:11:36 -04:00
Tom Lane c07d8c963e Adjust initdb to also not consider fsync'ing failures fatal.
Make initdb's version of this logic look as much like the backend's
as possible.  This is much less critical than in the backend since not
so many people use "initdb -S", but we want the same corner-case error
handling in both cases.

Back-patch to 9.3 where initdb -S option was introduced.  Before that,
initdb only had to deal with freshly-created data directories, wherein
no failures should be expected.

Abhijit Menon-Sen
2015-05-29 13:05:16 -04:00
Bruce Momjian 2200713aa8 initdb: only recommend pg_ctl to start the server
Previously we mentioned the 'postgres' binary method as well.
2015-05-11 12:14:57 -04:00
Bruce Momjian ed7b3b3811 initdb: remove unnecessary VACUUM FULL
Report by Peter Eisentraut
2015-03-31 11:51:39 -04:00
Andrew Dunstan fa1e5afa8a Run pg_upgrade and pg_resetxlog with restricted token on Windows
As with initdb these programs need to run with a restricted token, and
if they don't pg_upgrade will fail when run as a user with Adminstrator
privileges.

Backpatch to all live branches. On the development branch the code is
reorganized so that the restricted token code is now in a single
location. On the stable bramches a less invasive change is made by
simply copying the relevant code to pg_upgrade.c and pg_resetxlog.c.

Patches and bug report from Muhammad Asif Naeem, reviewed by Michael
Paquier, slightly edited by me.
2015-03-30 17:07:52 -04:00
Tom Lane 586dd5d6a5 Replace a bunch more uses of strncpy() with safer coding.
strncpy() has a well-deserved reputation for being unsafe, so make an
effort to get rid of nearly all occurrences in HEAD.

A large fraction of the remaining uses were passing length less than or
equal to the known strlen() of the source, in which case no null-padding
can occur and the behavior is equivalent to memcpy(), though doubtless
slower and certainly harder to reason about.  So just use memcpy() in
these cases.

In other cases, use either StrNCpy() or strlcpy() as appropriate (depending
on whether padding to the full length of the destination buffer seems
useful).

I left a few strncpy() calls alone in the src/timezone/ code, to keep it
in sync with upstream (the IANA tzcode distribution).  There are also a
few such calls in ecpg that could possibly do with more analysis.

AFAICT, none of these changes are more than cosmetic, except for the four
occurrences in fe-secure-openssl.c, which are in fact buggy: an overlength
source leads to a non-null-terminated destination buffer and ensuing
misbehavior.  These don't seem like security issues, first because no stack
clobber is possible and second because if your values of sslcert etc are
coming from untrusted sources then you've got problems way worse than this.
Still, it's undesirable to have unpredictable behavior for overlength
inputs, so back-patch those four changes to all active branches.
2015-01-24 13:05:42 -05:00
Bruce Momjian 4baaf863ec Update copyright for 2015
Backpatch certain files through 9.0
2015-01-06 11:43:47 -05:00
Tom Lane c340494235 Fix another poorly worded error message.
Spotted by Álvaro Herrera.
2014-12-17 13:22:07 -05:00
Heikki Linnakangas 198cbe0a0c Give a proper error message if initdb password file is empty.
Used to say just "could not read password from file "...": Success", which
isn't very informative.

Mats Erik Andersson. Backpatch to all supported versions.
2014-12-05 14:30:31 +02:00
Peter Eisentraut e86507d770 Move PG_AUTOCONF_FILENAME definition
Since this is not something that a user should change,
pg_config_manual.h was an inappropriate place for it.

In initdb.c, remove the use of the macro, because utils/guc.h can't be
included by non-backend code.  But we hardcode all the other
configuration file names there, so this isn't a disaster.
2014-12-03 19:54:01 -05:00
Alvaro Herrera 73c986adde Keep track of transaction commit timestamps
Transactions can now set their commit timestamp directly as they commit,
or an external transaction commit timestamp can be fed from an outside
system using the new function TransactionTreeSetCommitTsData().  This
data is crash-safe, and truncated at Xid freeze point, same as pg_clog.

This module is disabled by default because it causes a performance hit,
but can be enabled in postgresql.conf requiring only a server restart.

A new test in src/test/modules is included.

Catalog version bumped due to the new subdirectory within PGDATA and a
couple of new SQL functions.

Authors: Álvaro Herrera and Petr Jelínek

Reviewed to varying degrees by Michael Paquier, Andres Freund, Robert
Haas, Amit Kapila, Fujii Masao, Jaime Casanova, Simon Riggs, Steven
Singer, Peter Eisentraut
2014-12-03 11:53:02 -03:00
Andres Freund 522c85a6a2 Fix initdb --sync-only to also sync tablespaces.
630cd14426 added initdb --sync-only, for use by pg_upgrade, by just
exposing the existing fsync code. That's wrong, because initdb so far
had absolutely no reason to deal with tablespaces.

Fix --sync-only by additionally explicitly syncing each of the
tablespaces.

Backpatch to 9.3 where --sync-only was introduced.

Abhijit Menon-Sen and Andres Freund
2014-11-15 01:19:40 +01:00
Peter Eisentraut 49d182e61e initdb: Fix compiler error in USE_PREFETCH case 2014-10-19 00:45:40 -04:00
Peter Eisentraut 7feaccc217 Allow setting effective_io_concurrency even on unsupported systems
This matches the behavior of other parameters that are unsupported on
some systems (e.g., ssl).

Also document the default value.
2014-10-18 21:35:46 -04:00
Peter Eisentraut f25e0bf5e0 Small message fixes 2014-08-09 00:07:00 -04:00
Andres Freund a36a8fa376 Rename logical decoding's pg_llog directory to pg_logical.
The old name wasn't very descriptive as of actual contents of the
directory, which are historical snapshots in the snapshots/
subdirectory and mappingdata for rewritten tuples in
mappings/. There's been a fair amount of discussion what would be a
good name. I'm settling for pg_logical because it's likely that
further data around logical decoding and replication will need saving
in the future.

Also add the missing entry for the directory into storage.sgml's list
of PGDATA contents.

Bumps catversion as the data directories won't be compatible.
2014-07-02 21:07:47 +02:00
Tom Lane fbb1d7d73f Allow CREATE/ALTER DATABASE to manipulate datistemplate and datallowconn.
Historically these database properties could be manipulated only by
manually updating pg_database, which is error-prone and only possible for
superusers.  But there seems no good reason not to allow database owners to
set them for their databases, so invent CREATE/ALTER DATABASE options to do
that.  Adjust a couple of places that were doing it the hard way to use the
commands instead.

Vik Fearing, reviewed by Pavel Stehule
2014-07-01 20:10:38 -04:00
Tom Lane f62d417825 Fix unportable setvbuf() usage in initdb.
In yesterday's commit 2dc4f011fd, I tried
to force buffering of stdout/stderr in initdb to be what it is by
default when the program is run interactively on Unix (since that's how
most manual testing is done).  This tripped over the fact that Windows
doesn't support _IOLBF mode.  We dealt with that a long time ago in
syslogger.c by falling back to unbuffered mode on Windows.  Export that
solution in port.h and use it in initdb.

Back-patch to 8.4, like the previous commit.
2014-05-15 15:57:54 -04:00
Tom Lane 2dc4f011fd In initdb, ensure stdout/stderr buffering behavior is what we expect.
Since this program may print to either stdout or stderr, the relative
ordering of its messages depends on the buffering behavior of those files.
Force stdout to be line-buffered and stderr to be unbuffered, ensuring
that the behavior will match standard Unix interactive behavior, even
when stdout and stderr are rerouted to a file.

Per complaint from Tomas Vondra.  The particular case he pointed out is
new in HEAD, but issues of the same sort could arise in any branch with
other error messages, so back-patch to all branches.

I'm unsure whether we might not want to do this in other client programs
as well.  For the moment, just fix initdb.
2014-05-14 21:14:25 -04:00
Tom Lane 31a263237f Make initdb throw error for bad locale values.
Historically we've printed a complaint for a bad locale setting, but then
fallen back to the environment default.  Per discussion, this is not such
a great idea, because rectifying an erroneous locale choice post-initdb
(perhaps long after data has been loaded) could be enormously expensive.
Better to complain and give the user a chance to double-check things.

The behavior was particularly bad if the bad setting came from environment
variables rather than a bogus command-line switch: in that case not only
was there a fallback to C/SQL_ASCII, but the printed complaint was quite
unhelpful.  It's hard to be entirely sure what variables setlocale looked
at, but we can at least give a hint where the problem might be.

Per a complaint from Tomas Vondra.
2014-05-14 11:51:10 -04:00
Bruce Momjian 0a78320057 pgindent run for 9.4
This includes removing tabs after periods in C comments, which was
applied to back branches, so this change should not effect backpatching.
2014-05-06 12:12:18 -04:00
Heikki Linnakangas a692ee5870 Replace SYSTEMQUOTEs with Windows-specific wrapper functions.
It's easy to forget using SYSTEMQUOTEs when constructing command strings
for system() or popen(). Even if we fix all the places missing it now, it is
bound to be forgotten again in the future. Introduce wrapper functions that
do the the extra quoting for you, and get rid of SYSTEMQUOTEs in all the
callers.

We previosly used SYSTEMQUOTEs in all the hard-coded command strings, and
this doesn't change the behavior of those. But user-supplied commands, like
archive_command, restore_command, COPY TO/FROM PROGRAM calls, as well as
pgbench's \shell, will now gain an extra pair of quotes. That is desirable,
but if you have existing scripts or config files that include an extra
pair of quotes, those might need to be adjusted.

Reviewed by Amit Kapila and Tom Lane
2014-05-05 16:07:40 +03:00
Heikki Linnakangas 503de54621 Add missing SYSTEMQUOTEs
Some popen() calls were missing SYSTEMQUOTEs, which caused initdb and
pg_upgrade to fail on Windows, if the installation path contained both
spaces and @ signs.

Patch by Nikhil Deshpande. Backpatch to all supported versions.
2014-04-30 10:35:52 +03:00
Tom Lane cad4fe6455 Use AF_UNSPEC not PF_UNSPEC in getaddrinfo calls.
According to the Single Unix Spec and assorted man pages, you're supposed
to use the constants named AF_xxx when setting ai_family for a getaddrinfo
call.  In a few places we were using PF_xxx instead.  Use of PF_xxx
appears to be an ancient BSD convention that was not adopted by later
standardization.  On BSD and most later Unixen, it doesn't matter much
because those constants have equivalent values anyway; but nonetheless
this code is not per spec.

In the same vein, replace PF_INET by AF_INET in one socket() call, which
wasn't even consistent with the other socket() call in the same function
let alone the remainder of our code.

Per investigation of a Cygwin trouble report from Marco Atzeri.  It's
probably a long shot that this will fix his issue, but it's wrong in
any case.
2014-04-16 13:21:20 -04:00
Bruce Momjian 1494931d73 Remove MinGW readdir/errno bug workaround fixed on 2003-10-10 2014-03-21 13:47:37 -04:00
Bruce Momjian 6f03927fce Properly check for readdir/closedir() failures
Clear errno before calling readdir() and handle old MinGW errno bug
while adding full test coverage for readdir/closedir failures.

Backpatch through 8.4.
2014-03-21 13:45:11 -04:00
Bruce Momjian 242c2737fb C comments: remove odd blank lines after #ifdef WIN32 lines
A few more
2014-03-13 01:42:24 -04:00
Bruce Momjian 886c0be3f6 C comments: remove odd blank lines after #ifdef WIN32 lines 2014-03-13 01:34:42 -04:00
Robert Haas b89e151054 Introduce logical decoding.
This feature, building on previous commits, allows the write-ahead log
stream to be decoded into a series of logical changes; that is,
inserts, updates, and deletes and the transactions which contain them.
It is capable of handling decoding even across changes to the schema
of the effected tables.  The output format is controlled by a
so-called "output plugin"; an example is included.  To make use of
this in a real replication system, the output plugin will need to be
modified to produce output in the format appropriate to that system,
and to perform filtering.

Currently, information can be extracted from the logical decoding
system only via SQL; future commits will add the ability to stream
changes via walsender.

Andres Freund, with review and other contributions from many other
people, including Álvaro Herrera, Abhijit Menon-Sen, Peter Gheogegan,
Kevin Grittner, Robert Haas, Heikki Linnakangas, Fujii Masao, Abhijit
Menon-Sen, Michael Paquier, Simon Riggs, Craig Ringer, and Steve
Singer.
2014-03-03 16:32:18 -05:00
Stephen Frost b1aebbb6a8 Various Coverity-spotted fixes
A number of issues were identified by the Coverity scanner and are
addressed in this patch.  None of these appear to be security issues
and many are mostly cosmetic changes.

Short comments for each of the changes follows.

Correct the semi-colon placement in be-secure.c regarding SSL retries.
Remove a useless comparison-to-NULL in proc.c (value is dereferenced
  prior to this check and therefore can't be NULL).
Add checking of chmod() return values to initdb.
Fix a couple minor memory leaks in initdb.
Fix memory leak in pg_ctl- involves free'ing the config file contents.
Use an int to capture fgetc() return instead of an enum in pg_dump.
Fix minor memory leaks in pg_dump.
  (note minor change to convertOperatorReference()'s API)
Check fclose()/remove() return codes in psql.
Check fstat(), find_my_exec() return codes in psql.
Various ECPG memory leak fixes.
Check find_my_exec() return in ECPG.
Explicitly ignore pqFlush return in libpq error-path.
Change PQfnumber() to avoid doing an strdup() when no changes required.
Remove a few useless check-against-NULL's (value deref'd beforehand).
Check rmtree(), malloc() results in pg_regress.
Also check get_alternative_expectfile() return in pg_regress.
2014-03-01 22:14:14 -05:00
Peter Eisentraut 66c04c981d Mark some more variables as static or include the appropriate header
Detected by clang's -Wmissing-variable-declarations.

From: Andres Freund <andres@anarazel.de>
2014-02-08 21:21:46 -05:00
Robert Haas 858ec11858 Introduce replication slots.
Replication slots are a crash-safe data structure which can be created
on either a master or a standby to prevent premature removal of
write-ahead log segments needed by a standby, as well as (with
hot_standby_feedback=on) pruning of tuples whose removal would cause
replication conflicts.  Slots have some advantages over existing
techniques, as explained in the documentation.

In a few places, we refer to the type of replication slots introduced
by this patch as "physical" slots, because forthcoming patches for
logical decoding will also have slots, but with somewhat different
properties.

Andres Freund and Robert Haas
2014-01-31 22:45:36 -05:00