BufFileWrite across MAX_PHYSICAL_FILESIZE boundary
Just noticed buffile.c:292 doesn't look quite right where
BufFileDumpBuffer calls FileWrite:
bytestowrite = FileWrite(thisfile, file->buffer, bytestowrite);
It looks as though it would write the same data each time the
loop is iterated. Would this be better?
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);
"Kurt Harriman" <kharriman@greenplum.com> writes:
Just noticed buffile.c:292 doesn't look quite right where
BufFileDumpBuffer calls FileWrite:
bytestowrite = FileWrite(thisfile, file->buffer, bytestowrite);
It looks as though it would write the same data each time the
loop is iterated. Would this be better?
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);
Yeah, I think you're right. We've probably not seen this because in
most usages the buffer is always block-aligned, but it looks possible
for tuplestore.c to get out of alignment if its concurrent write/read
feature is exercised just so. Do you want to try demonstrating the bug
with a smaller-than-normal setting of MAX_PHYSICAL_FILESIZE?
regards, tom lane
This has been saved for the 8.4 release:
http://momjian.postgresql.org/cgi-bin/pgpatches_hold
---------------------------------------------------------------------------
Tom Lane wrote:
"Kurt Harriman" <kharriman@greenplum.com> writes:
Just noticed buffile.c:292 doesn't look quite right where
BufFileDumpBuffer calls FileWrite:
bytestowrite = FileWrite(thisfile, file->buffer, bytestowrite);
It looks as though it would write the same data each time the
loop is iterated. Would this be better?
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);Yeah, I think you're right. We've probably not seen this because in
most usages the buffer is always block-aligned, but it looks possible
for tuplestore.c to get out of alignment if its concurrent write/read
feature is exercised just so. Do you want to try demonstrating the bug
with a smaller-than-normal setting of MAX_PHYSICAL_FILESIZE?regards, tom lane
---------------------------(end of broadcast)---------------------------
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--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
Bruce Momjian wrote:
This has been saved for the 8.4 release:
Huh, no, this is a bug and should be fixed right away.
---------------------------------------------------------------------------
Tom Lane wrote:
"Kurt Harriman" <kharriman@greenplum.com> writes:
Just noticed buffile.c:292 doesn't look quite right where
BufFileDumpBuffer calls FileWrite:
bytestowrite = FileWrite(thisfile, file->buffer, bytestowrite);
It looks as though it would write the same data each time the
loop is iterated. Would this be better?
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);Yeah, I think you're right. We've probably not seen this because in
most usages the buffer is always block-aligned, but it looks possible
for tuplestore.c to get out of alignment if its concurrent write/read
feature is exercised just so. Do you want to try demonstrating the bug
with a smaller-than-normal setting of MAX_PHYSICAL_FILESIZE?
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
Alvaro Herrera wrote:
Bruce Momjian wrote:
This has been saved for the 8.4 release:
Huh, no, this is a bug and should be fixed right away.
OK, moved to the 8.3 patch queue.
---------------------------------------------------------------------------
---------------------------------------------------------------------------
Tom Lane wrote:
"Kurt Harriman" <kharriman@greenplum.com> writes:
Just noticed buffile.c:292 doesn't look quite right where
BufFileDumpBuffer calls FileWrite:
bytestowrite = FileWrite(thisfile, file->buffer, bytestowrite);
It looks as though it would write the same data each time the
loop is iterated. Would this be better?
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);Yeah, I think you're right. We've probably not seen this because in
most usages the buffer is always block-aligned, but it looks possible
for tuplestore.c to get out of alignment if its concurrent write/read
feature is exercised just so. Do you want to try demonstrating the bug
with a smaller-than-normal setting of MAX_PHYSICAL_FILESIZE?--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
I wrote:
"Kurt Harriman" <kharriman@greenplum.com> writes:
Just noticed buffile.c:292 doesn't look quite right where
BufFileDumpBuffer calls FileWrite:
bytestowrite = FileWrite(thisfile, file->buffer, bytestowrite);
It looks as though it would write the same data each time the
loop is iterated. Would this be better?
bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);
Yeah, I think you're right.
FYI, I was able to exercise the bug by changing RELSEG_SIZE to 2 within
buffile.c and then running this script in the regression database:
set work_mem = '64kB';
begin;
declare c scroll cursor for select * from tenk1 a join tenk1 b using(two);
fetch 1 from c;
fetch 100 from c;
fetch backward 10 from c;
fetch 100 from c;
fetch backward 10 from c;
fetch 100 from c;
fetch backward 100 from c;
commit;
It doesn't crash with the fix applied. Thanks for spotting it.
regards, tom lane