Full_Name: Howard Chu Version: HEAD OS: Linux URL: ftp://ftp.openldap.org/incoming/ Submission from: (NULL) (195.235.15.200) Submitted by: hyc I ran into some corruption problems when running a 64bit LMDB process concurrent with a 32bit one using MDB_VL32. While LMDB's own structures are all 64bit clean in a VL32 build, unfortunately pthread_mutex_t structures are not. In particular, in glibc a pthread_mutex_t can be one of 3 different sizes - 24 bytes for 32bit runtime on 32bit processor, 32 bytes for 32bit runtime on x86-64, and 40 bytes for 64bit runtime on x86-64. As such, we cannot safely share an LMDB environment between 32 and 64bit Linux processes, even when using MDB_VL32. This problem doesn't affect Windows, platforms using SysV semaphores, or platforms using POSIX named semaphores. I don't currently know whether this is a problem on other platforms that support POSIX process-shared mutexes. Hallvard has suggested that we add some additional LOCK_FORMAT bits to protect against incompatible accesses. This would primarily be useful for the mdb_stat command, which can still safely retrieve some useful information from an environment without acquiring any mutexes. E.g., an MDB_VL32 build of mdb_stat could retrieve most envinfo, statinfo, and readerinfo from a running 64bit environment. It could not scan the freelist, scan all the names of named DBs, or clean the reader list, since these operations all require taking the reader mutex.
changed state Open to Active moved from Incoming to Software Bugs
hyc@openldap.org wrote: > Full_Name: Howard Chu > Version: HEAD > OS: Linux > URL: ftp://ftp.openldap.org/incoming/ > Submission from: (NULL) (195.235.15.200) > Submitted by: hyc > > > I ran into some corruption problems when running a 64bit LMDB process concurrent > with a 32bit one using MDB_VL32. While LMDB's own structures are all 64bit clean > in a VL32 build, unfortunately pthread_mutex_t structures are not. In > particular, in glibc a pthread_mutex_t can be one of 3 different sizes - 24 > bytes for 32bit runtime on 32bit processor, 32 bytes for 32bit runtime on > x86-64, and 40 bytes for 64bit runtime on x86-64. As such, we cannot safely > share an LMDB environment between 32 and 64bit Linux processes, even when using > MDB_VL32. > > This problem doesn't affect Windows, platforms using SysV semaphores, or > platforms using POSIX named semaphores. I don't currently know whether this is a > problem on other platforms that support POSIX process-shared mutexes. For glibc, I've submitted an enhancement request regarding mutex sizes: https://sourceware.org/bugzilla/show_bug.cgi?id=21119 -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/