all local buffers @ xact commit, so accordingly nextFreeLocalBuf
is first local buffer now.
It helps to avoid unnecessary local buffer allocations in LocalBufferAlloc()
latter ("memmory leaks" in 'order by').
2. ResetLocalBufferPool() lost allocated local buffers:
memset(LocalBufferDescriptors, 0, sizeof(BufferDesc) * NLocBuffer);
(local buffers leak @ xact aborts).
fd = FileNameOpenFile(path, O_RDWR|O_CREAT|O_EXCL, 0600);
/*
* If the file already exists and is empty, we pretend that the
* create succeeded. During bootstrap processing, we skip that check,
* because pg_time, pg_variable, and pg_log get created before their
* .bki file entries are processed.
*
> * As the result of this pretence it was possible to have in
> * pg_class > 1 records with the same relname. Actually, it
> * should be fixed in upper levels, too, but... - vadim 05/06/97
> */
Reply-To: hackers@hub.org, Dan McGuirk <mcguirk@indirect.com>
To: hackers@hub.org
Subject: [HACKERS] tmin writeback optimization
I was doing some profiling of the backend, and noticed that during a certain
benchmark I was running somewhere between 30% and 75% of the backend's CPU
time was being spent in calls to TransactionIdDidCommit() from
HeapTupleSatisfiesNow() or HeapTupleSatisfiesItself() to determine that
changed rows' transactions had in fact been committed even though the rows'
tmin values had not yet been set.
When a query looks at a given row, it needs to figure out whether the
transaction that changed the row has been committed and hence it should pay
attention to the row, or whether on the other hand the transaction is still
in progress or has been aborted and hence the row should be ignored. If
a tmin value is set, it is known definitively that the row's transaction
has been committed. However, if tmin is not set, the transaction
referred to in xmin must be looked up in pg_log, and this is what the
backend was spending a lot of time doing during my benchmark.
So, implementing a method suggested by Vadim, I created the following
patch that, the first time a query finds a committed row whose tmin value
is not set, sets it, and marks the buffer where the row is stored as
dirty. (It works for tmax, too.) This doesn't result in the boost in
real time performance I was hoping for, however it does decrease backend
CPU usage by up to two-thirds in certain situations, so it could be
rather beneficial in high-concurrency settings.
Subject: [HACKERS] lock debug trace
This is an update to my previous patches for lock debugging, already applied
to the current sources. It adds some improvements in the output messages and
some more output in WaitOnLock(). I have used with success to trace a nasty
deadlock condition on pg_listener.
Subject: [HACKERS] linux/alpha patches
These patches lay the groundwork for a Linux/Alpha port. The port doesn't
actually work unless you tweak the linker to put all the pointers in the
first 32 bits of the address space, but it's at least a start. It
implements the test-and-set instruction in Alpha assembly, and also fixes
a lot of pointer-to-integer conversions, which is probably good anyway.
The following patches add to the backend a new debugging flag -K which prints
a debug trace of all locking operations on user relations (those with oid
greater than 20000). The code is compiled only if LOCK_MGR_DEBUG is defined,
so the patch should be harmless if not explicitly enabled.
I'm using the code to trace deadlock conditions caused by application queries
using the command "$POSTMASTER -D $PGDATA -o '-d 1 -K 1'.
The patches are for version 6.0 dated 970126.
1. New flag - BM_JUST_DIRTIED - added for BufferDesc;
2. All data "dirtiers" (WriteBuffer and WriteNoReleaseBuffer)
set this flag (and BM_DIRTY too);
3. All data "flushers" (FlushBuffer, BufferSync and BufferReplace)
turn this flag off just before calling smgr[blind]write/smgrflush
and check this flag after flushing buffer: if it turned ON then
BM_DIRTY will stay ON.
included after storage/ipc.h like other similar cases that were changed
recently.
This one has popped up during the last few days.
My sources are sup'ed today, 13. jan 1996.
regards
Erik Bertelsen.
Changes:
* Unique index capability works using the syntax 'create unique
index'.
* Duplicate OID's in the system tables are removed. I put
little scripts called 'duplicate_oids' and 'find_oid' in
include/catalog that help to find and remove duplicate OID's.
I also moved 'unused_oids' from backend/catalog to
include/catalog, since it has to be in the same directory
as the include files in order to work.
* The backend tries converting the name of a function or aggregate
to all lowercase if the original name given doesn't work (mostly
for compatibility with ODBC).
* You can 'SELECT NULL' to your heart's content.
* I put my _bt_updateitem fix in instead, which uses
_bt_insertonpg so that even if the new key is so big that
the page has to be split, everything still works.
* All literal references to system catalog OID's have been
replaced with references to define'd constants from the catalog
header files.
* I added a couple of node copy functions. I think this was a
preliminary attempt to get rules to work.
