Full_Name: Hallvard B Furuseth Version: LMDB_0.9.10 OS: Linux x86_64 URL: Submission from: (NULL) (81.191.45.35) Submitted by: hallvard

Uneven-sized keys in MDB_DUPSORT databases get unaligned sub-pages, and thus everything inside their sub-pages gets unaligned too.

A fix preserving the current format when !MISALIGNED_OK would be more memcpying, e.g. in COPY_PGNO(). dcmp functions would do byte by byte comparison for such sub-pages. MDB_page.mp_flags could be split two uint8_t fields: mp_flags, mp_zero (zero for now anyway). Renumber P_KEEP to 0x80 or P_META.

A fix with a format change would be to put the padding byte in front of the sub-page instead of at the end.

One fix with a format change could be that the data item gets uneven size too, with a padding byte in front of the sub-page.

The most general way would be to do that in all nodes with uneven- sized key and even-sized data:

#define NODEDATA(node) ((void *) ((char *)(node)->mn_data + \ (node)->mn_ksize + ((node)->mn_ksize & ~(node)->mn_lo & 1)))

Or do it only with sub-pages. Make the data item uneven-sized so code which is not interested in whether this is a sub-page, need not know about the hack. Access the sub-page specially:

#define NODEPAGE(node) ((MDB_page *) \ ((char *)(node)->mn_data + (((node)->mn_ksize + 1) & -2)))

That could be coded so the old format is still readable. Then a utility can walk all databases and adjust sub-pages so they have padding in front instead of at the end, so no dump/reload will be needed:

/** Address of the possibly 2-byte aligned sub-page in a node. * If the data item has uneven size, then the first byte is * padding to re-align the sub-page after an uneven-sized key. */ #define NODEPAGE(node) ((MDB_page *) \ ((char *)(node)->mn_data + (node)->mn_ksize + ((node)->mn_lo & 1)))