5 Commits (60f1e514ad0db017bc583b0e15d056b777bd9626)

Author	SHA1	Message	Date
Robert Haas	3761fe3c20	Simplify LWLock tranche machinery by removing array_base/array_stride. ... array_base and array_stride were added so that we could identify the offset of an LWLock within a tranche, but this facility is only very marginally used apart from the main tranche. So, give every lock in the main tranche its own tranche ID and get rid of array_base, array_stride, and all that's attached. For debugging facilities (Trace_lwlocks and LWLOCK_STATS) print the pointer address of the LWLock using %p instead of the offset. This is arguably more useful, and certainly a lot cheaper. Drop the offset-within-tranche from the information reported to dtrace and from one can't-happen message inside lwlock.c. The main user-visible impact of this change is that pg_stat_activity will now report all waits for LWLocks as "LWLock" rather than reporting some as "LWLockTranche" and others as "LWLockNamed". The main motivation for this change is that the need to specify an array_base and an array_stride is awkward for parallel query. There is only a very limited supply of tranche IDs so we can't just keep allocating new ones, and if we try to use the same tranche IDs every time then we run into trouble when multiple parallel contexts are use simultaneously. So if we didn't get rid of this mechanism we'd have to make it even more complicated. By simplifying it in this way, we instead reduce the size of the generated code for lwlock.c by about 5%. Discussion: http://postgr.es/m/CA+TgmoYsFn6NUW1x0AZtupJGUAs1UDY4dJtCN47_Q6D0sP80PA@mail.gmail.com	9 years ago
Robert Haas	2bbdc6875d	dsa: Cope with the possibility that SIZE_MAX is not defined. ... Per buildfarm member gaur and Tom Lane.	9 years ago
Robert Haas	88f626f868	Fix more DSA problems uncovered by the buildfarm. ... On 32-bit systems, don't try to use 64-bit DSA pointers, because the computation of DSA_MAX_SEGMENT_SIZE overflows Size. Cast 1 to Size before shifting it, so that the compiler doesn't produce a result of the wrong width. In passing, change one use of size_t to Size.	9 years ago
Robert Haas	670b3bc8f5	Try to fix some DSA-related compiler warnings. ... Commit 13df76a537 was overconfident about how portable %016lx is. Some compilers complain because they need %016llx, while platforms where DSA pointers are only 32 bits get unhappy about using a 64-bit format for a 32-bit quantity. Thomas Munro, per an off-list suggestion from me.	9 years ago
Robert Haas	13df76a537	Introduce dynamic shared memory areas. ... Programmers discovered decades ago that it was useful to have a simple interface for allocating and freeing memory, which is why malloc() and free() were invented. Unfortunately, those handy tools don't work with dynamic shared memory segments because those are specific to PostgreSQL and are not necessarily mapped at the same address in every cooperating process. So invent our own allocator instead. This makes it possible for processes cooperating as part of parallel query execution to allocate and free chunks of memory without having to reserve them prior to the start of execution. It could also be used for longer lived objects; for example, we could consider storing data for pg_stat_statements or the stats collector in shared memory using these interfaces, rather than writing them to files. Basically, anything that needs shared memory but can't predict in advance how much it's going to need might find this useful. Thomas Munro and Robert Haas. The original code (of mine) on which Thomas based his work was actually designed to be a new backend-local memory allocator for PostgreSQL, but that hasn't gone anywhere - or not yet, anyway. Thomas took that work and performed major refactoring and extensive modifications to make it work with dynamic shared memory, including the addition of appropriate locking. Discussion: CA+TgmobkeWptGwiNa+SGFWsTLzTzD-CeLz0KcE-y6LFgoUus4A@mail.gmail.com Discussion: CAEepm=1z5WLuNoJ80PaCvz6EtG9dN0j-KuHcHtU6QEfcPP5-qA@mail.gmail.com	9 years ago