the standby has written, flushed, and applied the WAL. At the moment, this
is for informational purposes only, the values are only shown in
pg_stat_replication system view, but in the future they will also be needed
for synchronous replication.
Extracted from Simon riggs' synchronous replication patch by Robert Haas, with
some tweaking by me.
Until now, our Serializable mode has in fact been what's called Snapshot
Isolation, which allows some anomalies that could not occur in any
serialized ordering of the transactions. This patch fixes that using a
method called Serializable Snapshot Isolation, based on research papers by
Michael J. Cahill (see README-SSI for full references). In Serializable
Snapshot Isolation, transactions run like they do in Snapshot Isolation,
but a predicate lock manager observes the reads and writes performed and
aborts transactions if it detects that an anomaly might occur. This method
produces some false positives, ie. it sometimes aborts transactions even
though there is no anomaly.
To track reads we implement predicate locking, see storage/lmgr/predicate.c.
Whenever a tuple is read, a predicate lock is acquired on the tuple. Shared
memory is finite, so when a transaction takes many tuple-level locks on a
page, the locks are promoted to a single page-level lock, and further to a
single relation level lock if necessary. To lock key values with no matching
tuple, a sequential scan always takes a relation-level lock, and an index
scan acquires a page-level lock that covers the search key, whether or not
there are any matching keys at the moment.
A predicate lock doesn't conflict with any regular locks or with another
predicate locks in the normal sense. They're only used by the predicate lock
manager to detect the danger of anomalies. Only serializable transactions
participate in predicate locking, so there should be no extra overhead for
for other transactions.
Predicate locks can't be released at commit, but must be remembered until
all the transactions that overlapped with it have completed. That means that
we need to remember an unbounded amount of predicate locks, so we apply a
lossy but conservative method of tracking locks for committed transactions.
If we run short of shared memory, we overflow to a new "pg_serial" SLRU
pool.
We don't currently allow Serializable transactions in Hot Standby mode.
That would be hard, because even read-only transactions can cause anomalies
that wouldn't otherwise occur.
Serializable isolation mode now means the new fully serializable level.
Repeatable Read gives you the old Snapshot Isolation level that we have
always had.
Kevin Grittner and Dan Ports, reviewed by Jeff Davis, Heikki Linnakangas and
Anssi Kääriäinen
As in commit fb4c5d2798 on 2011-01-21,
this avoids spurious debug messages and allows idempotent changes at
any time. Along the way, make assign_XactIsoLevel allow idempotent
changes even when not within a subtransaction, to be consistent with
the new coding of assign_transaction_read_only and because there's
no compelling reason to do otherwise.
Kevin Grittner, with some adjustments.
If wal_buffers is initially set to -1 (which is now the default), it's
replaced by 1/32nd of shared_buffers, with a minimum of 8 (the old default)
and a maximum of the XLOG segment size. The allowed range for manual
settings is still from 4 up to whatever will fit in shared memory.
Greg Smith, with implementation correction by me.
The new coding avoids a spurious debug message when a transaction
that has changed the isolation level has been rolled back. It also
allows the property to be freely changed to the current value within
a subtransaction.
Kevin Grittner, with one small change by me.
First, avoid scanning the whole ProcArray once we know there
are at least commit_siblings active; second, skip the check
altogether if commit_siblings = 0.
Greg Smith
This eliminates some crufty, special-purpose code and, as a non-trivial
side benefit, allows recovery.conf parameters to be unquoted.
Dimitri Fontaine, with review and cleanup by Alvaro Herrera, Itagaki
Takahiro, and me.
Rather than considering this result as meaning "unknown", report LONG_MAX.
This won't change what superusers can set max_stack_depth to, but it will
cause InitializeGUCOptions() to set the built-in default to 2MB not 100kB.
The latter seems like a fairly unreasonable interpretation of "infinity".
Per my investigation of odd buildfarm results as well as an old complaint
from Heikki.
Since this should persuade all the buildfarm animals to use a reasonable
stack depth setting during "make check", revert previous patch that dumbed
down a recursive regression test to only 5 levels.
Split the old typenameTypeId() into two functions: A new typenameTypeId() that
returns only a type OID, and typenameTypeIdAndMod() that returns type OID and
typmod. This isolates call sites better that actually care about the typmod.
Per gripe from Fujii Masao, though this is not exactly his proposed patch.
Categorize as DEVELOPER_OPTIONS and set context PGC_SIGHUP, as per Fujii,
but set the default to LOG because higher values aren't really sensible
(see the code for trace_recovery()). Fix the documentation to agree with
the code and to try to explain what the variable actually does. Get rid
of no-op calls trace_recovery(LOG), which accomplish nothing except to
demonstrate that this option confuses even its author.
This allows us to reliably remove all leftover temporary relation
files on cluster startup without reference to system catalogs or WAL;
therefore, we no longer include temporary relations in XLOG_XACT_COMMIT
and XLOG_XACT_ABORT WAL records.
Since these changes require including a backend ID in each
SharedInvalSmgrMsg, the size of the SharedInvalidationMessage.id
field has been reduced from two bytes to one, and the maximum number
of connections has been reduced from INT_MAX / 4 to 2^23-1. It would
be possible to remove these restrictions by increasing the size of
SharedInvalidationMessage by 4 bytes, but right now that doesn't seem
like a good trade-off.
Review by Jaime Casanova and Tom Lane.
I've added a quote_all_identifiers GUC which affects the behavior
of the backend, and a --quote-all-identifiers argument to pg_dump
and pg_dumpall which sets the GUC and also affects the quoting done
internally by those applications.
Design by Tom Lane; review by Alex Hunsaker; in response to bug #5488
filed by Hartmut Goebel.
Normally, we automatically restart after a backend crash, but in some
cases when PostgreSQL is invoked by clusterware it may be desirable to
suppress this behavior, so we provide an option which does this.
Since no existing GUC group quite fits, create a new group called
"error handling options" for this and the previously undocumented GUC
exit_on_error, which is now documented.
Review by Fujii Masao.
log files created by the syslogger process.
In passing, make unix_file_permissions display its value in octal, same
as log_file_mode now does.
Martin Pihlak
Per extensive discussion on pgsql-hackers. We are deliberately not
back-patching this even though the behavior of 8.3 and 8.4 is
unquestionably broken, for fear of breaking existing users of this
parameter. This incompatibility should be release-noted.
to have different values in different processes of the primary server.
Also put it into the "Streaming Replication" GUC category; it doesn't belong
in "Standby Servers" because you use it on the master not the standby.
In passing also correct guc.c's idea of wal_keep_segments' category.
max_standby_streaming_delay, and revise the implementation to avoid assuming
that timestamps found in WAL records can meaningfully be compared to clock
time on the standby server. Instead, the delay limits are compared to the
elapsed time since we last obtained a new WAL segment from archive or since
we were last "caught up" to WAL data arriving via streaming replication.
This avoids problems with clock skew between primary and standby, as well
as other corner cases that the original coding would misbehave in, such
as the primary server having significant idle time between transactions.
Per my complaint some time ago and considerable ensuing discussion.
Do some desultory editing on the hot standby documentation, too.
description for vacuum_defer_cleanup_age to the correct category.
Sections in postgresql.conf are also sorted in the same order with docs.
Per gripe by Fujii Masao, suggestion by Heikki Linnakangas, and patch by me.
MaxStandbyDelay. Use the GUC units mechanism for the value, and choose more
appropriate timestamp functions for performing tests with it. Make the
ps_activity manipulation in ResolveRecoveryConflictWithVirtualXIDs have
behavior similar to ps_activity code elsewhere, notably not updating the
display when update_process_title is off and not truncating the display
contents at an arbitrarily-chosen length. Improve the docs to be explicit
about what MaxStandbyDelay actually measures, viz the difference between
primary and standby servers' clocks, and the possible hazards if their clocks
aren't in sync.
confusion with streaming-replication settings. Also, change its default
value to "off", because of concern about executing new and poorly-tested
code during ordinary non-replicating operation. Per discussion.
In passing do some minor editing of related documentation.
archival or hot standby should be WAL-logged, instead of deducing that from
other options like archive_mode. This replaces recovery_connections GUC in
the primary, where it now has no effect, but it's still used in the standby
to enable/disable hot standby.
Remove the WAL-logging of "unlogged operations", like creating an index
without WAL-logging and fsyncing it at the end. Instead, we keep a copy of
the wal_mode setting and the settings that affect how much shared memory a
hot standby server needs to track master transactions (max_connections,
max_prepared_xacts, max_locks_per_xact) in pg_control. Whenever the settings
change, at server restart, write a WAL record noting the new settings and
update pg_control. This allows us to notice the change in those settings in
the standby at the right moment, they used to be included in checkpoint
records, but that meant that a changed value was not reflected in the
standby until the first checkpoint after the change.
Bump PG_CONTROL_VERSION and XLOG_PAGE_MAGIC. Whack XLOG_PAGE_MAGIC back to
the sequence it used to follow, before hot standby and subsequent patches
changed it to 0x9003.
than during define_custom_variable(). This entails rejecting an ALTER
command if the target variable doesn't have a known (non-placeholder)
definition, unless the calling user is superuser. When the variable *is*
known, we can correctly apply the rule that only superusers can issue ALTER
for SUSET parameters. This allows define_custom_variable to apply ALTER's
values for SUSET parameters at module load time, secure in the knowledge
that only a superuser could have set the ALTER value. This change fixes a
longstanding gotcha in the usage of SUSET-level custom parameters; which
is a good thing to fix now that plpgsql defines such a parameter.
Also, make the name of the GUC and the name of the backing variable match.
Alnong the way, clean up a couple of slight typographical errors in the
related docs.
The logic for determining whether to materialize has been significantly
overhauled for 9.0. In case there should be any doubt about whether
materialization is a win in any particular case, this should provide a
convenient way of seeing what happens without it; but even with enable_material
turned off, we still materialize in cases where it is required for
correctness.
Thanks to Tom Lane for the review.
doesn't take into account how far the WAL senders are. This way a hung
WAL sender doesn't prevent old WAL segments from being recycled/removed
in the primary, ultimately causing the disk to fill up. Instead add
standby_keep_segments setting to control how many old WAL segments are
kept in the primary. This also makes it more reliable to use streaming
replication without WAL archiving, assuming that you set
standby_keep_segments high enough.
The error message now makes explicit reference to the GUC that must be changed
to fix the problem, using wording suggested by Tom Lane. Along the way,
rename the GUC from MaxWalSenders to max_wal_senders for consistency and
grep-ability.
by a superuser -- "ALTER USER f RESET setting" already disallows removing such a
setting.
Apply the same treatment to ALTER DATABASE d RESET ALL when run by a database
owner that's not superuser.
how often we do SSL session key renegotiation. Can be set to
0 to disable renegotiation completely, which is required if
a broken SSL library is used (broken patches to CVE-2009-3555
a known cause) or when using a client library that can't do
renegotiation.
process. If startup waits on a buffer pin we send a request to all
backends to cancel themselves if they are holding the buffer pin
required and they are also waiting on a lock. If not, startup waits
until max_standby_delay before cancelling any backend waiting for
the requested buffer pin.
false positives during Hot Standby conflict processing. Simple
patch to enhance conflict processing, following previous discussions.
Controlled by parameter minimize_standby_conflicts = on | off, with
default off allows measurement of performance impact to see whether
it should be set on all the time.
default of "plpgsql". This is more reasonable than it was when the DO patch
was written, because we have since decided that plpgsql should be installed
by default. Per discussion, having a parameter for this doesn't seem useful
enough to justify the risk of application breakage if the value is changed
unexpectedly.
AbortTransaction or AbortSubTransaction, when trying to clean up after an
error that prevented (sub)transaction start from completing:
* access to TopTransactionResourceOwner that might not exist
* assert failure in AtEOXact_GUC, if AtStart_GUC not called yet
* assert failure or core dump in AfterTriggerEndSubXact, if
AfterTriggerBeginSubXact not called yet
Per testing by injecting elog(ERROR) at successive steps in StartTransaction
and StartSubTransaction. It's not clear whether all of these cases could
really occur in the field, but at least one of them is easily exposed by
simple stress testing, as per my accidental discovery yesterday.
woken by alarm we send SIGUSR1 to all backends requesting that they
check to see if they are blocking Startup process. If so, they throw
ERROR/FATAL as for other conflict resolutions. Deadlock stop gap
removed. max_standby_delay = -1 option removed to prevent deadlock.
This includes two new kinds of postmaster processes, walsenders and
walreceiver. Walreceiver is responsible for connecting to the primary server
and streaming WAL to disk, while walsender runs in the primary server and
streams WAL from disk to the client.
Documentation still needs work, but the basics are there. We will probably
pull the replication section to a new chapter later on, as well as the
sections describing file-based replication. But let's do that as a separate
patch, so that it's easier to see what has been added/changed. This patch
also adds a new section to the chapter about FE/BE protocol, documenting the
protocol used by walsender/walreceivxer.
Bump catalog version because of two new functions,
pg_last_xlog_receive_location() and pg_last_xlog_replay_location(), for
monitoring the progress of replication.
Fujii Masao, with additional hacking by me
we're not going to support that anymore.
I did keep the 64-bit-CRC-with-32-bit-arithmetic code, since it has a
performance excuse to live. It's a bit moot since that's all ifdef'd
out, of course.
Heikki Linnakangas
Robert Haas
Tom Lane
Bruce Momjian
Magnus Hagander
Simon Riggs
Peter Eisentraut
Itagaki Takahiro
Alvaro Herrera