diff options
Diffstat (limited to 'src/include/postgres.h')
| -rw-r--r-- | src/include/postgres.h | 58 |
1 files changed, 28 insertions, 30 deletions
diff --git a/src/include/postgres.h b/src/include/postgres.h index 8dea56a4f4..02b7056b54 100644 --- a/src/include/postgres.h +++ b/src/include/postgres.h @@ -7,7 +7,7 @@ * Client-side code should include postgres_fe.h instead. * * - * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group + * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group * Portions Copyright (c) 1995, Regents of the University of California * Portions Copyright (c) 2010-2012 Postgres-XC Development Group * @@ -55,11 +55,11 @@ */ /* - * struct varatt_external is a "TOAST pointer", that is, the information needed - * to fetch a Datum stored in an out-of-line on-disk Datum. The data is - * compressed if and only if va_extsize < va_rawsize - VARHDRSZ. This struct - * must not contain any padding, because we sometimes compare pointers using - * memcmp. + * struct varatt_external is a traditional "TOAST pointer", that is, the + * information needed to fetch a Datum stored out-of-line in a TOAST table. + * The data is compressed if and only if va_extsize < va_rawsize - VARHDRSZ. + * This struct must not contain any padding, because we sometimes compare + * these pointers using memcmp. * * Note that this information is stored unaligned within actual tuples, so * you need to memcpy from the tuple into a local struct variable before @@ -75,22 +75,23 @@ typedef struct varatt_external } varatt_external; /* - * Out-of-line Datum thats stored in memory in contrast to varatt_external - * pointers which points to data in an external toast relation. + * struct varatt_indirect is a "TOAST pointer" representing an out-of-line + * Datum that's stored in memory, not in an external toast relation. + * The creator of such a Datum is entirely responsible that the referenced + * storage survives for as long as referencing pointer Datums can exist. * - * Note that just as varatt_external's this is stored unaligned within the - * tuple. + * Note that just as for struct varatt_external, this struct is stored + * unaligned within any containing tuple. */ typedef struct varatt_indirect { struct varlena *pointer; /* Pointer to in-memory varlena */ } varatt_indirect; - /* - * Type of external toast datum stored. The peculiar value for VARTAG_ONDISK - * comes from the requirement for on-disk compatibility with the older - * definitions of varattrib_1b_e where v_tag was named va_len_1be... + * Type tag for the various sorts of "TOAST pointer" datums. The peculiar + * value for VARTAG_ONDISK comes from a requirement for on-disk compatibility + * with a previous notion that the tag field was the pointer datum's length. */ typedef enum vartag_external { @@ -99,9 +100,9 @@ typedef enum vartag_external } vartag_external; #define VARTAG_SIZE(tag) \ - ((tag) == VARTAG_INDIRECT ? sizeof(varatt_indirect) : \ + ((tag) == VARTAG_INDIRECT ? sizeof(varatt_indirect) : \ (tag) == VARTAG_ONDISK ? sizeof(varatt_external) : \ - TrapMacro(true, "unknown vartag")) + TrapMacro(true, "unrecognized TOAST vartag")) /* * These structs describe the header of a varlena object that may have been @@ -117,28 +118,28 @@ typedef union struct /* Normal varlena (4-byte length) */ { uint32 va_header; - char va_data[1]; + char va_data[FLEXIBLE_ARRAY_MEMBER]; } va_4byte; struct /* Compressed-in-line format */ { uint32 va_header; uint32 va_rawsize; /* Original data size (excludes header) */ - char va_data[1]; /* Compressed data */ + char va_data[FLEXIBLE_ARRAY_MEMBER]; /* Compressed data */ } va_compressed; } varattrib_4b; typedef struct { uint8 va_header; - char va_data[1]; /* Data begins here */ + char va_data[FLEXIBLE_ARRAY_MEMBER]; /* Data begins here */ } varattrib_1b; -/* inline portion of a short varlena pointing to an external resource */ +/* TOAST pointers are a subset of varattrib_1b with an identifying tag byte */ typedef struct { uint8 va_header; /* Always 0x80 or 0x01 */ uint8 va_tag; /* Type of datum */ - char va_data[1]; /* Data (of the type indicated by va_tag) */ + char va_data[FLEXIBLE_ARRAY_MEMBER]; /* Type-specific data */ } varattrib_1b_e; /* @@ -163,8 +164,8 @@ typedef struct * this lets us disambiguate alignment padding bytes from the start of an * unaligned datum. (We now *require* pad bytes to be filled with zero!) * - * In TOAST datums the tag field in varattrib_1b_e is used to discern whether - * its an indirection pointer or more commonly an on-disk tuple. + * In TOAST pointers the va_tag field (see varattrib_1b_e) is used to discern + * the specific type and length of the pointer datum. */ /* @@ -681,16 +682,13 @@ extern Datum Float8GetDatum(float8 X); */ /* - * These declarations supports the assertion-related macros in c.h. - * assert_enabled is here because that file doesn't have PGDLLIMPORT in the - * right place, and ExceptionalCondition must be present, for the backend only, - * even when assertions are not enabled. + * Backend only infrastructure for the assertion-related macros in c.h. + * + * ExceptionalCondition must be present even when assertions are not enabled. */ -extern PGDLLIMPORT bool assert_enabled; - extern void ExceptionalCondition(const char *conditionName, const char *errorType, - const char *fileName, int lineNumber) __attribute__((noreturn)); + const char *fileName, int lineNumber) pg_attribute_noreturn(); //#define PGXC_COORD // for PGXC coordinator compiling //#define PGXC_DATANODE // for PGXC data node compiling |