Thread: pgsql: Checkpoint sorting and balancing.
Checkpoint sorting and balancing. Up to now checkpoints were written in the order they're in the BufferDescriptors. That's nearly random in a lot of cases, which performs badly on rotating media, but even on SSDs it causes slowdowns. To avoid that, sort checkpoints before writing them out. We currently sort by tablespace, relfilenode, fork and block number. One of the major reasons that previously wasn't done, was fear of imbalance between tablespaces. To address that balance writes between tablespaces. The other prime concern was that the relatively large allocation to sort the buffers in might fail, preventing checkpoints from happening. Thus pre-allocate the required memory in shared memory, at server startup. This particularly makes it more efficient to have checkpoint flushing enabled, because that'll often result in a lot of writes that can be coalesced into one flush. Discussion: alpine.DEB.2.10.1506011320000.28433@sto Author: Fabien Coelho and Andres Freund Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/9cd00c457e6a1ebb984167ac556a9961812a683c Modified Files -------------- src/backend/storage/buffer/README | 5 - src/backend/storage/buffer/buf_init.c | 22 ++- src/backend/storage/buffer/bufmgr.c | 274 +++++++++++++++++++++++++++++----- src/include/storage/buf_internals.h | 18 +++ src/tools/pgindent/typedefs.list | 2 + 5 files changed, 277 insertions(+), 44 deletions(-)
On 3/10/16 8:29 PM, Andres Freund wrote:
> Checkpoint sorting and balancing.
This patch appears to have introduced a change that makes the build
with dtrace fail:
In file included from ../../../../src/include/pg_trace.h:15:0,
from bufmgr.c:42:
bufmgr.c: In function 'BufferSync':
bufmgr.c:1939:59: error: 'num_to_write' undeclared (first use in this function)
TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_write);
^
../../../../src/include/utils/probes.h:93:83: note: in definition of macro 'TRACE_POSTGRESQL_BUFFER_SYNC_DONE'
__dtrace_probe$postgresql$buffer__sync__done$v1$696e74$696e74$696e74(arg0, arg1, arg2); \
^~~~
bufmgr.c:1939:59: note: each undeclared identifier is reported only once for each function it appears in
TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_write);
^
../../../../src/include/utils/probes.h:93:83: note: in definition of macro 'TRACE_POSTGRESQL_BUFFER_SYNC_DONE'
__dtrace_probe$postgresql$buffer__sync__done$v1$696e74$696e74$696e74(arg0, arg1, arg2); \
^~~~
On 2016-03-10 20:47:10 -0500, Peter Eisentraut wrote: > On 3/10/16 8:29 PM, Andres Freund wrote: > > Checkpoint sorting and balancing. > > This patch appears to have introduced a change that makes the build > with dtrace fail: > > In file included from ../../../../src/include/pg_trace.h:15:0, > from bufmgr.c:42: > bufmgr.c: In function 'BufferSync': > bufmgr.c:1939:59: error: 'num_to_write' undeclared (first use in this function) > TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_write); > ^ > ../../../../src/include/utils/probes.h:93:83: note: in definition of macro 'TRACE_POSTGRESQL_BUFFER_SYNC_DONE' > __dtrace_probe$postgresql$buffer__sync__done$v1$696e74$696e74$696e74(arg0, arg1, arg2); \ > ^~~~ > bufmgr.c:1939:59: note: each undeclared identifier is reported only once for each function it appears in > TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_write); > ^ > ../../../../src/include/utils/probes.h:93:83: note: in definition of macro 'TRACE_POSTGRESQL_BUFFER_SYNC_DONE' > __dtrace_probe$postgresql$buffer__sync__done$v1$696e74$696e74$696e74(arg0, arg1, arg2); \ > ^~~~ Hrmpf. I tried to fix the issue; could you quickly verify? These probes are a bit annoying; and I seriously doubt anybody actually uses them. But obviously we should keep them working as long as we have them. Thanks! Andres
On 3/10/16 8:52 PM, Andres Freund wrote: > Hrmpf. I tried to fix the issue; could you quickly verify? looks good
On Fri, Mar 11, 2016 at 2:29 AM, Andres Freund <andres@anarazel.de> wrote: > Checkpoint sorting and balancing. +1. -- Michael