Commit Graph

73 Commits

Author SHA1 Message Date
David Rowley 29f6a959cf Introduce a bump memory allocator
This introduces a bump MemoryContext type.  The bump context is best
suited for short-lived memory contexts which require only allocations
of memory and never a pfree or repalloc, which are unsupported.

Memory palloc'd into a bump context has no chunk header.  This makes
bump a useful context type when lots of small allocations need to be
done without any need to pfree those allocations.  Allocation sizes are
rounded up to the next MAXALIGN boundary, so with this and no chunk
header, allocations are very compact indeed.

Allocations are also very fast as bump does not check any freelists to
try and make use of previously free'd chunks.  It just checks if there
is enough room on the current block, and if so it bumps the freeptr
beyond this chunk and returns the value that the freeptr was previously
pointing to.  Simple and fast.  A new block is malloc'd when there's not
enough space in the current block.

Code using the bump allocator must take care never to call any functions
which could try to call realloc() (or variants), pfree(),
GetMemoryChunkContext() or GetMemoryChunkSpace() on a bump allocated
chunk.  Due to lack of chunk headers, these operations are unsupported.
To increase the chances of catching such issues, when compiled with
MEMORY_CONTEXT_CHECKING, bump allocated chunks are given a header and
any attempt to perform an unsupported operation will result in an ERROR.
Without MEMORY_CONTEXT_CHECKING, code attempting an unsupported
operation could result in a segfault.

A follow-on commit will implement the first user of bump.

Author: David Rowley
Reviewed-by: Nathan Bossart
Reviewed-by: Matthias van de Meent
Reviewed-by: Tomas Vondra
Reviewed-by: John Naylor
Discussion: https://postgr.es/m/CAApHDvqGSpCU95TmM=Bp=6xjL_nLys4zdZOpfNyWBk97Xrdj2w@mail.gmail.com
2024-04-08 00:02:43 +12:00
David Rowley 743112a2e9 Adjust memory allocation functions to allow sibling calls
Many modern compilers are able to optimize function calls to functions
where the parameters of the called function match a leading subset of
the calling function's parameters.  If there are no instructions in the
calling function after the function is called, then the compiler is free
to avoid any stack frame setup and implement the function call as a
"jmp" rather than a "call".  This is called sibling call optimization.

Here we adjust the memory allocation functions in mcxt.c to allow this
optimization.  This requires moving some responsibility into the memory
context implementations themselves.  It's now the responsibility of the
MemoryContext to check for malloc failures.  This is good as it both
allows the sibling call optimization, but also because most small and
medium allocations won't call malloc and just allocate memory to an
existing block.  That can't fail, so checking for NULLs in that case
isn't required.

Also, traditionally it's been the responsibility of palloc and the other
allocation functions in mcxt.c to check for invalid allocation size
requests.  Here we also move the responsibility of checking that into the
MemoryContext.  This isn't to allow the sibling call optimization, but
more because most of our allocators handle large allocations separately
and we can just add the size check when doing large allocations.  We no
longer check this for non-large allocations at all.

To make checking the allocation request sizes and ERROR handling easier,
add some helper functions to mcxt.c for the allocators to use.

Author: Andres Freund
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/20210719195950.gavgs6ujzmjfaiig@alap3.anarazel.de
2024-02-27 16:39:42 +13:00
Bruce Momjian 29275b1d17 Update copyright for 2024
Reported-by: Michael Paquier

Discussion: https://postgr.es/m/ZZKTDPxBBMt3C0J9@paquier.xyz

Backpatch-through: 12
2024-01-03 20:49:05 -05:00
Bruce Momjian c8e1ba736b Update copyright for 2023
Backpatch-through: 11
2023-01-02 15:00:37 -05:00
David Rowley c6e0fe1f2a Improve performance of and reduce overheads of memory management
Whenever we palloc a chunk of memory, traditionally, we prefix the
returned pointer with a pointer to the memory context to which the chunk
belongs.  This is required so that we're able to easily determine the
owning context when performing operations such as pfree() and repalloc().

For the AllocSet context, prior to this commit we additionally prefixed
the pointer to the owning context with the size of the chunk.  This made
the header 16 bytes in size.  This 16-byte overhead was required for all
AllocSet allocations regardless of the allocation size.

For the generation context, the problem was worse; in addition to the
pointer to the owning context and chunk size, we also stored a pointer to
the owning block so that we could track the number of freed chunks on a
block.

The slab allocator had a 16-byte chunk header.

The changes being made here reduce the chunk header size down to just 8
bytes for all 3 of our memory context types.  For small to medium sized
allocations, this significantly increases the number of chunks that we can
fit on a given block which results in much more efficient use of memory.

Additionally, this commit completely changes the rule that pointers to
palloc'd memory must be directly prefixed by a pointer to the owning
memory context and instead, we now insist that they're directly prefixed
by an 8-byte value where the least significant 3-bits are set to a value
to indicate which type of memory context the pointer belongs to.  Using
those 3 bits as an index (known as MemoryContextMethodID) to a new array
which stores the methods for each memory context type, we're now able to
pass the pointer given to functions such as pfree() and repalloc() to the
function specific to that context implementation to allow them to devise
their own methods of finding the memory context which owns the given
allocated chunk of memory.

The reason we're able to reduce the chunk header down to just 8 bytes is
because of the way we make use of the remaining 61 bits of the required
8-byte chunk header.  Here we also implement a general-purpose MemoryChunk
struct which makes use of those 61 remaining bits to allow the storage of
a 30-bit value which the MemoryContext is free to use as it pleases, and
also the number of bytes which must be subtracted from the chunk to get a
reference to the block that the chunk is stored on (also 30 bits).  The 1
additional remaining bit is to denote if the chunk is an "external" chunk
or not.  External here means that the chunk header does not store the
30-bit value or the block offset.  The MemoryContext can use these
external chunks at any time, but must use them if any of the two 30-bit
fields are not large enough for the value(s) that need to be stored in
them.  When the chunk is marked as external, it is up to the MemoryContext
to devise its own means to determine the block offset.

Using 3-bits for the MemoryContextMethodID does mean we're limiting
ourselves to only having a maximum of 8 different memory context types.
We could reduce the bit space for the 30-bit value a little to make way
for more than 3 bits, but it seems like it might be better to do that only
if we ever need more than 8 context types.  This would only be a problem
if some future memory context type which does not use MemoryChunk really
couldn't give up any of the 61 remaining bits in the chunk header.

With this MemoryChunk, each of our 3 memory context types can quickly
obtain a reference to the block any given chunk is located on.  AllocSet
is able to find the context to which the chunk is owned, by first
obtaining a reference to the block by subtracting the block offset as is
stored in the 'hdrmask' field and then referencing the block's 'aset'
field.  The Generation context uses the same method, but GenerationBlock
did not have a field pointing back to the owning context, so one is added
by this commit.

In aset.c and generation.c, all allocations larger than allocChunkLimit
are stored on dedicated blocks.  When there's just a single chunk on a
block like this, it's easy to find the block from the chunk, we just
subtract the size of the block header from the chunk pointer.  The size of
these chunks is also known as we store the endptr on the block, so we can
just subtract the pointer to the allocated memory from that.  Because we
can easily find the owning block and the size of the chunk for these
dedicated blocks, we just always use external chunks for allocation sizes
larger than allocChunkLimit.  For generation.c, this sidesteps the problem
of non-external MemoryChunks being unable to represent chunk sizes >= 1GB.
This is less of a problem for aset.c as we store the free list index in
the MemoryChunk's spare 30-bit field (the value of which will never be
close to using all 30-bits).  We can easily reverse engineer the chunk size
from this when needed.  Storing this saves AllocSetFree() from having to
make a call to AllocSetFreeIndex() to determine which free list to put the
newly freed chunk on.

For the slab allocator, this commit adds a new restriction that slab
chunks cannot be >= 1GB in size.  If there happened to be any users of
slab.c which used chunk sizes this large, they really should be using
AllocSet instead.

Here we also add a restriction that normal non-dedicated blocks cannot be
1GB or larger.  It's now not possible to pass a 'maxBlockSize' >= 1GB
during the creation of an AllocSet or Generation context.  Allocations can
still be larger than 1GB, it's just these will always be on dedicated
blocks (which do not have the 1GB restriction).

Author: Andres Freund, David Rowley
Discussion: https://postgr.es/m/CAApHDvpjauCRXcgcaL6+e3eqecEHoeRm9D-kcbuvBitgPnW=vw@mail.gmail.com
2022-08-29 17:15:00 +12:00
Tom Lane b4f79d278f Mark PlanState as an abstract node type.
In the same vein as commit 251154beb, make it clear that we never
instantiate PlanState.

Also mark MemoryContextData as abstract.  This has no effect right now,
since memnodes.h isn't one of the files fed to gen_node_support.pl.
But it seems like good documentation and future-proofing.
2022-07-09 13:35:37 -04:00
Bruce Momjian 27b77ecf9f Update copyright for 2022
Backpatch-through: 10
2022-01-07 19:04:57 -05:00
Fujii Masao 43620e3286 Add function to log the memory contexts of specified backend process.
Commit 3e98c0bafb added pg_backend_memory_contexts view to display
the memory contexts of the backend process. However its target process
is limited to the backend that is accessing to the view. So this is
not so convenient when investigating the local memory bloat of other
backend process. To improve this situation, this commit adds
pg_log_backend_memory_contexts() function that requests to log
the memory contexts of the specified backend process.

This information can be also collected by calling
MemoryContextStats(TopMemoryContext) via a debugger. But
this technique cannot be used in some environments because no debugger
is available there. So, pg_log_backend_memory_contexts() allows us to
see the memory contexts of specified backend more easily.

Only superusers are allowed to request to log the memory contexts
because allowing any users to issue this request at an unbounded rate
would cause lots of log messages and which can lead to denial of service.

On receipt of the request, at the next CHECK_FOR_INTERRUPTS(),
the target backend logs its memory contexts at LOG_SERVER_ONLY level,
so that these memory contexts will appear in the server log but not
be sent to the client. It logs one message per memory context.
Because if it buffers all memory contexts into StringInfo to log them
as one message, which may require the buffer to be enlarged very much
and lead to OOM error since there can be a large number of memory
contexts in a backend.

When a backend process is consuming huge memory, logging all its
memory contexts might overrun available disk space. To prevent this,
now this patch limits the number of child contexts to log per parent
to 100. As with MemoryContextStats(), it supposes that practical cases
where the log gets long will typically be huge numbers of siblings
under the same parent context; while the additional debugging value
from seeing details about individual siblings beyond 100 will not be large.

There was another proposed patch to add the function to return
the memory contexts of specified backend as the result sets,
instead of logging them, in the discussion. However that patch is
not included in this commit because it had several issues to address.

Thanks to Tatsuhito Kasahara, Andres Freund, Tom Lane, Tomas Vondra,
Michael Paquier, Kyotaro Horiguchi and Zhihong Yu for the discussion.

Bump catalog version.

Author: Atsushi Torikoshi
Reviewed-by: Kyotaro Horiguchi, Zhihong Yu, Fujii Masao
Discussion: https://postgr.es/m/0271f440ac77f2a4180e0e56ebd944d1@oss.nttdata.com
2021-04-06 13:44:15 +09:00
Bruce Momjian ca3b37487b Update copyright for 2021
Backpatch-through: 9.5
2021-01-02 13:06:25 -05:00
Jeff Davis 2fd6a44ad5 Revert "Specialize MemoryContextMemAllocated()."
This reverts commit e00912e11a.
2020-03-19 12:21:50 -07:00
Jeff Davis e00912e11a Specialize MemoryContextMemAllocated().
An AllocSet doubles the size of allocated blocks (up to maxBlockSize),
which means that the current block can represent half of the total
allocated space for the memory context. But the free space in the
current block may never have been touched, so don't count the
untouched memory as allocated for the purposes of
MemoryContextMemAllocated().

Discussion: https://postgr.es/m/ec63d70b668818255486a83ffadc3aec492c1f57.camel@j-davis.com
2020-03-18 15:39:14 -07:00
Bruce Momjian 7559d8ebfa Update copyrights for 2020
Backpatch-through: update all files in master, backpatch legal files through 9.4
2020-01-01 12:21:45 -05:00
Tomas Vondra f2369bc610 Use Size instead of int64 to track allocated memory
Commit 5dd7fc1519 added block-level memory accounting, but used int64 variable to
track the amount of allocated memory. That is incorrect, because we have Size for
exactly these purposes, but it was mostly harmless until c477f3e449 which changed
how we handle with repalloc() when downsizing the chunk. Previously we've ignored
these cases and just kept using the original chunk, but now we need to update the
accounting, and the code was doing this:

    context->mem_allocated += blksize - oldblksize;

Both blksize and oldblksize are Size (so unsigned) which means the subtraction
underflows, producing a very high positive value. On 64-bit platforms (where Size
has the same size as mem_alllocated) this happens to work because the result wraps
to the right value, but on (some) 32-bit platforms this fails.

This fixes two things - it changes mem_allocated (and related variables) to Size,
and it splits the update to two separate steps, to prevent any underflows.

Discussion: https://www.postgresql.org/message-id/15151.1570163761%40sss.pgh.pa.us
2019-10-04 16:10:56 +02:00
Tomas Vondra 5dd7fc1519 Add transparent block-level memory accounting
Adds accounting of memory allocated in a memory context. Compared to
various ad hoc solutions, the main advantage is that the accounting is
transparent and does not require direct control over allocations (this
matters for use cases where the allocations happen in user code, like
for example aggregate states allocated in a transition functions).

To reduce overhead, the accounting happens at the block level (not for
individual chunks) and only the context immediately owning the block is
updated. When inquiring about amount of memory allocated in a context,
we have to recursively walk all children contexts.

This "lazy" accounting works well for cases with relatively small number
of contexts in the relevant subtree and/or with infrequent inquiries.

Author: Jeff Davis
Reivewed-by: Tomas Vondra, Melanie Plageman, Soumyadeep Chakraborty
Discussion: https://www.postgresql.org/message-id/flat/027a129b8525601c6a680d27ce3a7172dab61aab.camel@j-davis.com
2019-10-01 03:13:39 +02:00
Bruce Momjian 97c39498e5 Update copyright for 2019
Backpatch-through: certain files through 9.4
2019-01-02 12:44:25 -05:00
Tom Lane 442accc3fe Allow memory contexts to have both fixed and variable ident strings.
Originally, we treated memory context names as potentially variable in
all cases, and therefore always copied them into the context header.
Commit 9fa6f00b1 rethought this a little bit and invented a distinction
between fixed and variable names, skipping the copy step for the former.
But we can make things both simpler and more useful by instead allowing
there to be two parts to a context's identification, a fixed "name" and
an optional, variable "ident".  The name supplied in the context create
call is now required to be a compile-time-constant string in all cases,
as it is never copied but just pointed to.  The "ident" string, if
wanted, is supplied later.  This is needed because typically we want
the ident to be stored inside the context so that it's cleaned up
automatically on context deletion; that means it has to be copied into
the context before we can set the pointer.

The cost of this approach is basically just an additional pointer field
in struct MemoryContextData, which isn't much overhead, and is bought
back entirely in the AllocSet case by not needing a headerSize field
anymore, since we no longer have to cope with variable header length.
In addition, we can simplify the internal interfaces for memory context
creation still further, saving a few cycles there.  And it's no longer
true that a custom identifier disqualifies a context from participating
in aset.c's freelist scheme, so possibly there's some win on that end.

All the places that were using non-compile-time-constant context names
are adjusted to put the variable info into the "ident" instead.  This
allows more effective identification of those contexts in many cases;
for example, subsidary contexts of relcache entries are now identified
by both type (e.g. "index info") and relname, where before you got only
one or the other.  Contexts associated with PL function cache entries
are now identified more fully and uniformly, too.

I also arranged for plancache contexts to use the query source string
as their identifier.  This is basically free for CachedPlanSources, as
they contained a copy of that string already.  We pay an extra pstrdup
to do it for CachedPlans.  That could perhaps be avoided, but it would
make things more fragile (since the CachedPlanSource is sometimes
destroyed first).  I suspect future improvements in error reporting will
require CachedPlans to have a copy of that string anyway, so it's not
clear that it's worth moving mountains to avoid it now.

This also changes the APIs for context statistics routines so that the
context-specific routines no longer assume that output goes straight
to stderr, nor do they know all details of the output format.  This
is useful immediately to reduce code duplication, and it also allows
for external code to do something with stats output that's different
from printing to stderr.

The reason for pushing this now rather than waiting for v12 is that
it rethinks some of the API changes made by commit 9fa6f00b1.  Seems
better for extension authors to endure just one round of API changes
not two.

Discussion: https://postgr.es/m/CAB=Je-FdtmFZ9y9REHD7VsSrnCkiBhsA4mdsLKSPauwXtQBeNA@mail.gmail.com
2018-03-27 16:46:51 -04:00
Bruce Momjian 9d4649ca49 Update copyright for 2018
Backpatch-through: certain files through 9.3
2018-01-02 23:30:12 -05:00
Tom Lane 9fa6f00b13 Rethink MemoryContext creation to improve performance.
This patch makes a number of interrelated changes to reduce the overhead
involved in creating/deleting memory contexts.  The key ideas are:

* Include the AllocSetContext header of an aset.c context in its first
malloc request, rather than allocating it separately in TopMemoryContext.
This means that we now always create an initial or "keeper" block in an
aset, even if it never receives any allocation requests.

* Create freelists in which we can save and recycle recently-destroyed
asets (this idea is due to Robert Haas).

* In the common case where the name of a context is a constant string,
just store a pointer to it in the context header, rather than copying
the string.

The first change eliminates a palloc/pfree cycle per context, and
also avoids bloat in TopMemoryContext, at the price that creating
a context now involves a malloc/free cycle even if the context never
receives any allocations.  That would be a loser for some common
usage patterns, but recycling short-lived contexts via the freelist
eliminates that pain.

Avoiding copying constant strings not only saves strlen() and strcpy()
overhead, but is an essential part of the freelist optimization because
it makes the context header size constant.  Currently we make no
attempt to use the freelist for contexts with non-constant names.
(Perhaps someday we'll need to think harder about that, but in current
usage, most contexts with custom names are long-lived anyway.)

The freelist management in this initial commit is pretty simplistic,
and we might want to refine it later --- but in common workloads that
will never matter because the freelists will never get full anyway.

To create a context with a non-constant name, one is now required to
call AllocSetContextCreateExtended and specify the MEMCONTEXT_COPY_NAME
option.  AllocSetContextCreate becomes a wrapper macro, and it includes
a test that will complain about non-string-literal context name
parameters on gcc and similar compilers.

An unfortunate side effect of making AllocSetContextCreate a macro is
that one is now *required* to use the size parameter abstraction macros
(ALLOCSET_DEFAULT_SIZES and friends) with it; the pre-9.6 habit of
writing out individual size parameters no longer works unless you
switch to AllocSetContextCreateExtended.

Internally to the memory-context-related modules, the context creation
APIs are simplified, removing the rather baroque original design whereby
a context-type module called mcxt.c which then called back into the
context-type module.  That saved a bit of code duplication, but not much,
and it prevented context-type modules from exercising control over the
allocation of context headers.

In passing, I converted the test-and-elog validation of aset size
parameters into Asserts to save a few more cycles.  The original thought
was that callers might compute size parameters on the fly, but in practice
nobody does that, so it's useless to expend cycles on checking those
numbers in production builds.

Also, mark the memory context method-pointer structs "const",
just for cleanliness.

Discussion: https://postgr.es/m/2264.1512870796@sss.pgh.pa.us
2017-12-13 13:55:16 -05:00
Simon Riggs a4ccc1cef5 Generational memory allocator
Add new style of memory allocator, known as Generational
appropriate for use in cases where memory is allocated
and then freed in roughly oldest first order (FIFO).

Use new allocator for logical decoding’s reorderbuffer
to significantly reduce memory usage and improve performance.

Author: Tomas Vondra
Reviewed-by: Simon Riggs
2017-11-23 05:45:07 +11:00
Tom Lane c7b8998ebb Phase 2 of pgindent updates.
Change pg_bsd_indent to follow upstream rules for placement of comments
to the right of code, and remove pgindent hack that caused comments
following #endif to not obey the general rule.

Commit e3860ffa4d wasn't actually using
the published version of pg_bsd_indent, but a hacked-up version that
tried to minimize the amount of movement of comments to the right of
code.  The situation of interest is where such a comment has to be
moved to the right of its default placement at column 33 because there's
code there.  BSD indent has always moved right in units of tab stops
in such cases --- but in the previous incarnation, indent was working
in 8-space tab stops, while now it knows we use 4-space tabs.  So the
net result is that in about half the cases, such comments are placed
one tab stop left of before.  This is better all around: it leaves
more room on the line for comment text, and it means that in such
cases the comment uniformly starts at the next 4-space tab stop after
the code, rather than sometimes one and sometimes two tabs after.

Also, ensure that comments following #endif are indented the same
as comments following other preprocessor commands such as #else.
That inconsistency turns out to have been self-inflicted damage
from a poorly-thought-through post-indent "fixup" in pgindent.

This patch is much less interesting than the first round of indent
changes, but also bulkier, so I thought it best to separate the effects.

Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
2017-06-21 15:19:25 -04:00
Tom Lane e3860ffa4d Initial pgindent run with pg_bsd_indent version 2.0.
The new indent version includes numerous fixes thanks to Piotr Stefaniak.
The main changes visible in this commit are:

* Nicer formatting of function-pointer declarations.
* No longer unexpectedly removes spaces in expressions using casts,
  sizeof, or offsetof.
* No longer wants to add a space in "struct structname *varname", as
  well as some similar cases for const- or volatile-qualified pointers.
* Declarations using PG_USED_FOR_ASSERTS_ONLY are formatted more nicely.
* Fixes bug where comments following declarations were sometimes placed
  with no space separating them from the code.
* Fixes some odd decisions for comments following case labels.
* Fixes some cases where comments following code were indented to less
  than the expected column 33.

On the less good side, it now tends to put more whitespace around typedef
names that are not listed in typedefs.list.  This might encourage us to
put more effort into typedef name collection; it's not really a bug in
indent itself.

There are more changes coming after this round, having to do with comment
indentation and alignment of lines appearing within parentheses.  I wanted
to limit the size of the diffs to something that could be reviewed without
one's eyes completely glazing over, so it seemed better to split up the
changes as much as practical.

Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
2017-06-21 14:39:04 -04:00
Andres Freund 58b25e9810 Add "Slab" MemoryContext implementation for efficient equal-sized allocations.
The default general purpose aset.c style memory context is not a great
choice for allocations that are all going to be evenly sized,
especially when those objects aren't small, and have varying
lifetimes.  There tends to be a lot of fragmentation, larger
allocations always directly go to libc rather than have their cost
amortized over several pallocs.

These problems lead to the introduction of ad-hoc slab allocators in
reorderbuffer.c. But it turns out that the simplistic implementation
leads to problems when a lot of objects are allocated and freed, as
aset.c is still the underlying implementation. Especially freeing can
easily run into O(n^2) behavior in aset.c.

While the O(n^2) behavior in aset.c can, and probably will, be
addressed, custom allocators for this behavior are more efficient
both in space and time.

This allocator is for evenly sized allocations, and supports both
cheap allocations and freeing, without fragmenting significantly.  It
does so by allocating evenly sized blocks via malloc(), and carves
them into chunks that can be used for allocations.  In order to
release blocks to the OS as early as possible, chunks are allocated
from the fullest block that still has free objects, increasing the
likelihood of a block being entirely unused.

A subsequent commit uses this in reorderbuffer.c, but a further
allocator is needed to resolve the performance problems triggering
this work.

There likely are further potentialy uses of this allocator besides
reorderbuffer.c.

There's potential further optimizations of the new slab.c, in
particular the array of freelists could be replaced by a more
intelligent structure - but for now this looks more than good enough.

Author: Tomas Vondra, editorialized by Andres Freund
Reviewed-By: Andres Freund, Petr Jelinek, Robert Haas, Jim Nasby
Discussion: https://postgr.es/m/d15dff83-0b37-28ed-0809-95a5cc7292ad@2ndquadrant.com
2017-02-27 03:41:44 -08:00
Bruce Momjian 1d25779284 Update copyright via script for 2017 2017-01-03 13:48:53 -05:00
Bruce Momjian ee94300446 Update copyright for 2016
Backpatch certain files through 9.1
2016-01-02 13:33:40 -05:00
Kevin Grittner 25c5392330 Improve performance in freeing memory contexts
The single linked list of memory contexts could result in O(N^2)
performance to free a set of contexts if they were not freed in
reverse order of creation.  In many cases the reverse order was
used, but there were some significant exceptions that caused real-
world performance problems.  Rather than requiring all callers to
care about the order in which contexts were freed, and hunting down
and changing all existing cases where the wrong order was used, we
add one pointer per memory context so that the implementation
details are not so visible.

Jan Wieck
2015-12-08 17:32:49 -06:00
Tom Lane 7b5ef8f2d0 Limit the verbosity of memory context statistics dumps.
We had a report from Stefan Kaltenbrunner of a case in which postmaster
log files overran available disk space because multiple backends spewed
enormous context stats dumps upon hitting an out-of-memory condition.
Given the lack of similar reports, this isn't a common problem, but it
still seems worth doing something about.  However, we don't want to just
blindly truncate the output, because that might prevent diagnosis of OOM
problems.  What seems like a workable compromise is to limit the dump to
100 child contexts per parent, and summarize the space used within any
additional child contexts.  That should help because practical cases where
the dump gets long will typically be huge numbers of siblings under the
same parent context; while the additional debugging value from seeing
details about individual siblings beyond 100 will not be large, we hope.
Anyway it doesn't take much code or memory space to do this, so let's try
it like this and see how things go.

Since the summarization mechanism requires passing totals back up anyway,
I took the opportunity to add a "grand total" line to the end of the
printout.
2015-08-25 13:09:48 -04:00
Tom Lane 097fe194aa Move memory context callback declarations into palloc.h.
Initial experience with this feature suggests that instances of
MemoryContextCallback are likely to propagate into some widely-used headers
over time.  As things stood, that would result in pulling memutils.h or
at least memnodes.h into common headers, which does not seem desirable.
Instead, let's decide that this feature is part of the "ordinary palloc
user" API rather than the "specialized context management" API, and as
such should be declared in palloc.h not memutils.h.
2015-03-01 12:31:32 -05:00
Tom Lane f65e827058 Invent a memory context reset/delete callback mechanism.
This allows cleanup actions to be registered to be called just before a
particular memory context's contents are flushed (either by deletion or
MemoryContextReset).  The patch in itself has no use-cases for this, but
several likely reasons for wanting this exist.

In passing, per discussion, rearrange some boolean fields in struct
MemoryContextData so as to avoid wasted padding space.  For safety,
this requires making allowInCritSection's existence unconditional;
but I think that's a better approach than what was there anyway.
2015-02-27 17:16:43 -05:00
Bruce Momjian 4baaf863ec Update copyright for 2015
Backpatch certain files through 9.0
2015-01-06 11:43:47 -05:00
Heikki Linnakangas 1c6821be31 Fix and enhance the assertion of no palloc's in a critical section.
The assertion failed if WAL_DEBUG or LWLOCK_STATS was enabled; fix that by
using separate memory contexts for the allocations made within those code
blocks.

This patch introduces a mechanism for marking any memory context as allowed
in a critical section. Previously ErrorContext was exempt as a special case.

Instead of a blanket exception of the checkpointer process, only exempt the
memory context used for the pending ops hash table.
2014-06-30 10:26:00 +03:00
Bruce Momjian 7e04792a1c Update copyright for 2014
Update all files in head, and files COPYRIGHT and legal.sgml in all back
branches.
2014-01-07 16:05:30 -05:00
Bruce Momjian bd61a623ac Update copyrights for 2013
Fully update git head, and update back branches in ./COPYRIGHT and
legal.sgml files.
2013-01-01 17:15:01 -05:00
Bruce Momjian e126958c2e Update copyright notices for year 2012. 2012-01-01 18:01:58 -05:00
Heikki Linnakangas 30e98a7e6e Pull up isReset flag from AllocSetContext to MemoryContext struct. This
avoids the overhead of one function call when calling MemoryContextReset(),
and it seems like the isReset optimization would be applicable to any new
memory context we might invent in the future anyway.

This buys back the overhead I just added in previous patch to always call
MemoryContextReset() in ExecScan, even when there's no quals or projections.
2011-05-21 14:47:19 -04:00
Bruce Momjian 5d950e3b0c Stamp copyrights for year 2011. 2011-01-01 13:18:15 -05:00
Magnus Hagander 9f2e211386 Remove cvs keywords from all files. 2010-09-20 22:08:53 +02:00
Bruce Momjian 0239800893 Update copyright for the year 2010. 2010-01-02 16:58:17 +00:00
Peter Eisentraut de160e2c00 Make backend header files C++ safe
This alters various incidental uses of C++ key words to use other similar
identifiers, so that a C++ compiler won't choke outright.  You still
(probably) need extern "C" { }; around the inclusion of backend headers.

based on a patch by Kurt Harriman <harriman@acm.org>

Also add a script cpluspluscheck to check for C++ compatibility in the
future.  As of right now, this passes without error for me.
2009-07-16 06:33:46 +00:00
Bruce Momjian 511db38ace Update copyright for 2009. 2009-01-01 17:24:05 +00:00
Bruce Momjian 9098ab9e32 Update copyrights in source tree to 2008. 2008-01-01 19:46:01 +00:00
Neil Conway 849ec99753 Adjust the output of MemoryContextStats() so that the stats for a
child memory contexts is indented two spaces to the right of its
parent context.  This should make it easier to deduce the memory
context hierarchy from the output of MemoryContextStats().
2007-08-07 06:25:14 +00:00
Bruce Momjian 29dccf5fe0 Update CVS HEAD for 2007 copyright. Back branches are typically not
back-stamped for this.
2007-01-05 22:20:05 +00:00
Bruce Momjian f2f5b05655 Update copyright for 2006. Update scripts. 2006-03-05 15:59:11 +00:00
PostgreSQL Daemon 2ff501590b Tag appropriate files for rc3
Also performed an initial run through of upgrading our Copyright date to
extend to 2005 ... first run here was very simple ... change everything
where: grep 1996-2004 && the word 'Copyright' ... scanned through the
generated list with 'less' first, and after, to make sure that I only
picked up the right entries ...
2004-12-31 22:04:05 +00:00
Tom Lane 257cccbe5e Add some marginal tweaks to eliminate memory leakages associated with
subtransactions.  Trivial subxacts (such as a plpgsql exception block
containing no database access) now demonstrably leak zero bytes.
2004-09-16 20:17:49 +00:00
Bruce Momjian da9a8649d8 Update copyright to 2004. 2004-08-29 04:13:13 +00:00
PostgreSQL Daemon 55b113257c make sure the $Id tags are converted to $PostgreSQL as well ... 2003-11-29 22:41:33 +00:00
Bruce Momjian f3c3deb7d0 Update copyrights to 2003. 2003-08-04 02:40:20 +00:00
Tom Lane 77a7e9968b Change memory-space accounting mechanism in tuplesort.c and tuplestore.c
to make a reasonable attempt at accounting for palloc overhead, not just
the requested size of each memory chunk.  Since in many scenarios this
will make for a significant reduction in the amount of space acquired,
partially compensate by doubling the default value of SORT_MEM to 1Mb.
Per discussion in pgsql-general around 9-Jun-2002..
2002-08-12 00:36:12 +00:00
Bruce Momjian d84fe82230 Update copyright to 2002. 2002-06-20 20:29:54 +00:00