PMEMPOOL_SYNC(3)

NAME

pmempool_sync(), pmempool_transform() - pool set synchronization and transformation

SYNOPSIS

    #include <libpmempool.h>
    int pmempool_sync(const char *poolset_file,
        unsigned flags); (EXPERIMENTAL)
    int pmempool_transform(const char *poolset_file_src,
        const char *poolset_file_dst, unsigned flags); (EXPERIMENTAL)

DESCRIPTION

The pmempool_sync() function synchronizes data between replicas within a pool set.

pmempool_sync() accepts two arguments:

•   poolset_file - a path to a pool set file,

•   flags - a combination of flags (ORed) which modify how synchronization is performed.

    NOTE: Only the pool set file used to create the pool should be used for syncing the pool.

    NOTE: The pmempool_sync() cannot do anything useful if there are no replicas in the pool set. In such case, it fails with an error.

    NOTE: At the moment, replication is only supported for libpmemobj(7) pools, so pmempool_sync() cannot be used with other pool types (libpmemlog(7), libpmemblk(7)).

The following flags are available:

•   PMEMPOOL_SYNC_DRY_RUN - do not apply changes, only check for viability of synchronization.

pmempool_sync() checks that the metadata of all replicas in a pool set is consistent, i.e. all parts are healthy, and if any of them is not, the corrupted or missing parts are recreated and filled with data from one of the healthy replicas.

If a pool set has the option SINGLEHDR (see poolset(5)), the internal metadata of each replica is limited to the beginning of the first part in the replica. If the option NOHDRS is used, replicas contain no internal metadata. In both cases, only the missing parts or the ones which cannot be opened are recreated with the pmempool_sync() function.

pmempool_transform() modifies the internal structure of a pool set. It supports the following operations:

•   adding one or more replicas,

•   removing one or more replicas ,

•   adding or removing pool set options.

Only one of the above operations can be performed at a time.

pmempool_transform() accepts three arguments:

•   poolset_file_src - pathname of the pool set file for the source pool set to be changed,

•   poolset_file_dst - pathname of the pool set file that defines the new structure of the pool set,

•   flags - a combination of flags (ORed) which modify how synchronization is performed.

The following flags are available:

•   PMEMPOOL_TRANSFORM_DRY_RUN - do not apply changes, only check for viability of transformation.

When adding or deleting replicas, the two pool set files can differ only in the definitions of replicas which are to be added or deleted. When adding or removing pool set options (see poolset(5)), the rest of both pool set files have to be of the same structure. The operation of adding/removing a pool set option can be performed on a pool set with local replicas only. To add/remove a pool set option to/from a pool set with remote replicas, one has to remove the remote replicas first, then add/remove the option, and finally recreate the remote replicas having added/removed the pool set option to/from the remote replicas' poolset files. To add a replica it is necessary for its effective size to match or exceed the pool size. Otherwise the whole operation fails and no changes are applied. If none of the pool set options is used, the effective size of a replica is the sum of sizes of all its part files decreased by 4096 bytes per each part file. The 4096 bytes of each part file is utilized for storing internal metadata of the pool part files. If the option SINGLEHDR is used, the effective size of a replica is the sum of sizes of all its part files decreased once by 4096 bytes. In this case only the first part contains internal metadata. If the option NOHDRS is used, the effective size of a replica is the sum of sizes of all its part files. In this case none of the parts contains internal metadata.

    NOTE: At the moment, transform operation is only supported for libpmemobj(7) pools, so pmempool_transform() cannot be used with other pool types (libpmemlog(7), libpmemblk(7)).

RETURN VALUE

pmempool_sync() and pmempool_transform() return 0 on success. Otherwise, they return -1 and set errno appropriately.

ERRORS

EINVAL Invalid format of the input/output pool set file.

EINVAL Unsupported flags value.

EINVAL There is only master replica defined in the input pool set passed to pmempool_sync().

EINVAL The source pool set passed to pmempool_transform() is not a libpmemobj pool.

EINVAL The input and output pool sets passed to pmempool_transform() are identical.

EINVAL Attempt to perform more than one transform operation at a time.

ENOTSUP The pool set contains a remote replica, but remote replication is not supported (librpmem(7) is not available).

NOTES

The pmempool_sync() API is experimental and it may change in future versions of the library.

The pmempool_transform() API is experimental and it may change in future versions of the library.

SEE ALSO

libpmemlog(7), libpmemobj(7) and <https://pmem.io>