Minor cleanup/code review for "indirect toast" stuff.
Fix some issues I noticed while fooling with an extension to allow an additional kind of toast pointer. Much of this is just comment improvement, but there are a couple of actual bugs, which might or might not be reachable today depending on what can happen during logical decoding. An example is that toast_flatten_tuple() failed to cover the possibility of an indirection pointer in its input. Back-patch to 9.4 just in case that is reachable now. In HEAD, also correct some really minor issues with recent compression reorganization, such as dangerously underparenthesized macros.
This commit is contained in:
Tom Lane
parent
c619c2351f
commit
bc4de01db3
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@ -50,7 +50,7 @@
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*/
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typedef struct toast_compress_header
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{
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int32 vl_len_; /* varlena header (do not touch directly!) */
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int32 vl_len_; /* varlena header (do not touch directly!) */
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int32 rawsize;
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} toast_compress_header;
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@ -58,12 +58,12 @@ typedef struct toast_compress_header
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* Utilities for manipulation of header information for compressed
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* toast entries.
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*/
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#define TOAST_COMPRESS_HDRSZ ((int32) sizeof(toast_compress_header))
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#define TOAST_COMPRESS_RAWSIZE(ptr) (((toast_compress_header *) ptr)->rawsize)
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#define TOAST_COMPRESS_HDRSZ ((int32) sizeof(toast_compress_header))
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#define TOAST_COMPRESS_RAWSIZE(ptr) (((toast_compress_header *) (ptr))->rawsize)
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#define TOAST_COMPRESS_RAWDATA(ptr) \
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(((char *) ptr) + TOAST_COMPRESS_HDRSZ)
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(((char *) (ptr)) + TOAST_COMPRESS_HDRSZ)
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#define TOAST_COMPRESS_SET_RAWSIZE(ptr, len) \
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(((toast_compress_header *) ptr)->rawsize = len)
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(((toast_compress_header *) (ptr))->rawsize = (len))
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static void toast_delete_datum(Relation rel, Datum value);
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static Datum toast_save_datum(Relation rel, Datum value,
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@ -90,8 +90,9 @@ static void toast_close_indexes(Relation *toastidxs, int num_indexes,
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*
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* This will return a datum that contains all the data internally, ie, not
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* relying on external storage or memory, but it can still be compressed or
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* have a short header.
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----------
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* have a short header. Note some callers assume that if the input is an
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* EXTERNAL datum, the result will be a pfree'able chunk.
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* ----------
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*/
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struct varlena *
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heap_tuple_fetch_attr(struct varlena * attr)
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@ -108,9 +109,7 @@ heap_tuple_fetch_attr(struct varlena * attr)
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else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
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{
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/*
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* copy into the caller's memory context. That's not required in all
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* cases but sufficient for now since this is mainly used when we need
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* to persist a Datum for unusually long time, like in a HOLD cursor.
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* This is an indirect pointer --- dereference it
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*/
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struct varatt_indirect redirect;
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@ -120,11 +119,14 @@ heap_tuple_fetch_attr(struct varlena * attr)
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/* nested indirect Datums aren't allowed */
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Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));
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/* doesn't make much sense, but better handle it */
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if (VARATT_IS_EXTERNAL_ONDISK(attr))
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/* recurse if value is still external in some other way */
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if (VARATT_IS_EXTERNAL(attr))
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return heap_tuple_fetch_attr(attr);
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/* copy datum verbatim */
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/*
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* Copy into the caller's memory context, in case caller tries to
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* pfree the result.
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*/
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result = (struct varlena *) palloc(VARSIZE_ANY(attr));
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memcpy(result, attr, VARSIZE_ANY(attr));
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}
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@ -144,7 +146,10 @@ heap_tuple_fetch_attr(struct varlena * attr)
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* heap_tuple_untoast_attr -
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*
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* Public entry point to get back a toasted value from compression
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* or external storage.
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* or external storage. The result is always non-extended varlena form.
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*
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* Note some callers assume that if the input is an EXTERNAL or COMPRESSED
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* datum, the result will be a pfree'able chunk.
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* ----------
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*/
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struct varlena *
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@ -160,12 +165,16 @@ heap_tuple_untoast_attr(struct varlena * attr)
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if (VARATT_IS_COMPRESSED(attr))
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{
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struct varlena *tmp = attr;
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attr = toast_decompress_datum(tmp);
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pfree(tmp);
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}
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}
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else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
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{
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/*
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* This is an indirect pointer --- dereference it
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*/
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struct varatt_indirect redirect;
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VARATT_EXTERNAL_GET_POINTER(redirect, attr);
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@ -174,7 +183,18 @@ heap_tuple_untoast_attr(struct varlena * attr)
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/* nested indirect Datums aren't allowed */
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Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));
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/* recurse in case value is still extended in some other way */
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attr = heap_tuple_untoast_attr(attr);
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/* if it isn't, we'd better copy it */
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if (attr == (struct varlena *) redirect.pointer)
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{
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struct varlena *result;
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result = (struct varlena *) palloc(VARSIZE_ANY(attr));
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memcpy(result, attr, VARSIZE_ANY(attr));
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attr = result;
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}
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}
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else if (VARATT_IS_COMPRESSED(attr))
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{
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@ -246,9 +266,12 @@ heap_tuple_untoast_attr_slice(struct varlena * attr,
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else
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preslice = attr;
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Assert(!VARATT_IS_EXTERNAL(preslice));
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if (VARATT_IS_COMPRESSED(preslice))
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{
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struct varlena *tmp = preslice;
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preslice = toast_decompress_datum(tmp);
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if (tmp != attr)
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@ -448,8 +471,6 @@ toast_delete(Relation rel, HeapTuple oldtup)
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continue;
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else if (VARATT_IS_EXTERNAL_ONDISK(PointerGetDatum(value)))
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toast_delete_datum(rel, value);
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else if (VARATT_IS_EXTERNAL_INDIRECT(PointerGetDatum(value)))
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elog(ERROR, "attempt to delete tuple containing indirect datums");
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}
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}
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}
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@ -611,7 +632,8 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
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/*
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* We took care of UPDATE above, so any external value we find
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* still in the tuple must be someone else's we cannot reuse.
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* still in the tuple must be someone else's that we cannot reuse
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* (this includes the case of an out-of-line in-memory datum).
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* Fetch it back (without decompression, unless we are forcing
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* PLAIN storage). If necessary, we'll push it out as a new
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* external value below.
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@ -1043,7 +1065,7 @@ toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
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new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
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if (VARATT_IS_EXTERNAL(new_value))
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{
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new_value = toast_fetch_datum(new_value);
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new_value = heap_tuple_fetch_attr(new_value);
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toast_values[i] = PointerGetDatum(new_value);
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toast_free[i] = true;
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}
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@ -1746,8 +1768,8 @@ toast_fetch_datum(struct varlena * attr)
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int num_indexes;
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int validIndex;
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if (VARATT_IS_EXTERNAL_INDIRECT(attr))
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elog(ERROR, "shouldn't be called for indirect tuples");
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if (!VARATT_IS_EXTERNAL_ONDISK(attr))
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elog(ERROR, "toast_fetch_datum shouldn't be called for non-ondisk datums");
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/* Must copy to access aligned fields */
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VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
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@ -1923,7 +1945,8 @@ toast_fetch_datum_slice(struct varlena * attr, int32 sliceoffset, int32 length)
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int num_indexes;
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int validIndex;
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Assert(VARATT_IS_EXTERNAL_ONDISK(attr));
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if (!VARATT_IS_EXTERNAL_ONDISK(attr))
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elog(ERROR, "toast_fetch_datum_slice shouldn't be called for non-ondisk datums");
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/* Must copy to access aligned fields */
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VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
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@ -96,10 +96,10 @@
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VARHDRSZ)
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/* Size of an EXTERNAL datum that contains a standard TOAST pointer */
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#define TOAST_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(struct varatt_external))
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#define TOAST_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_external))
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/* Size of an indirect datum that contains a standard TOAST pointer */
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#define INDIRECT_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(struct varatt_indirect))
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/* Size of an EXTERNAL datum that contains an indirection pointer */
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#define INDIRECT_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_indirect))
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/*
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* Testing whether an externally-stored value is compressed now requires
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@ -54,11 +54,11 @@
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*/
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/*
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* struct varatt_external is a "TOAST pointer", that is, the information needed
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* to fetch a Datum stored in an out-of-line on-disk Datum. The data is
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* compressed if and only if va_extsize < va_rawsize - VARHDRSZ. This struct
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* must not contain any padding, because we sometimes compare pointers using
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* memcmp.
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* struct varatt_external is a traditional "TOAST pointer", that is, the
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* information needed to fetch a Datum stored out-of-line in a TOAST table.
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* The data is compressed if and only if va_extsize < va_rawsize - VARHDRSZ.
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* This struct must not contain any padding, because we sometimes compare
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* these pointers using memcmp.
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*
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* Note that this information is stored unaligned within actual tuples, so
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* you need to memcpy from the tuple into a local struct variable before
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@ -74,22 +74,23 @@ typedef struct varatt_external
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} varatt_external;
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/*
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* Out-of-line Datum thats stored in memory in contrast to varatt_external
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* pointers which points to data in an external toast relation.
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* struct varatt_indirect is a "TOAST pointer" representing an out-of-line
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* Datum that's stored in memory, not in an external toast relation.
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* The creator of such a Datum is entirely responsible that the referenced
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* storage survives for as long as referencing pointer Datums can exist.
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*
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* Note that just as varatt_external's this is stored unaligned within the
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* tuple.
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* Note that just as for struct varatt_external, this struct is stored
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* unaligned within any containing tuple.
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*/
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typedef struct varatt_indirect
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{
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struct varlena *pointer; /* Pointer to in-memory varlena */
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} varatt_indirect;
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/*
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* Type of external toast datum stored. The peculiar value for VARTAG_ONDISK
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* comes from the requirement for on-disk compatibility with the older
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* definitions of varattrib_1b_e where v_tag was named va_len_1be...
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* Type tag for the various sorts of "TOAST pointer" datums. The peculiar
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* value for VARTAG_ONDISK comes from a requirement for on-disk compatibility
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* with a previous notion that the tag field was the pointer datum's length.
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*/
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typedef enum vartag_external
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{
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@ -98,9 +99,9 @@ typedef enum vartag_external
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} vartag_external;
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#define VARTAG_SIZE(tag) \
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((tag) == VARTAG_INDIRECT ? sizeof(varatt_indirect) : \
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((tag) == VARTAG_INDIRECT ? sizeof(varatt_indirect) : \
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(tag) == VARTAG_ONDISK ? sizeof(varatt_external) : \
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TrapMacro(true, "unknown vartag"))
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TrapMacro(true, "unrecognized TOAST vartag"))
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/*
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* These structs describe the header of a varlena object that may have been
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@ -132,7 +133,7 @@ typedef struct
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char va_data[1]; /* Data begins here */
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} varattrib_1b;
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/* inline portion of a short varlena pointing to an external resource */
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/* TOAST pointers are a subset of varattrib_1b with an identifying tag byte */
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typedef struct
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{
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uint8 va_header; /* Always 0x80 or 0x01 */
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@ -162,8 +163,8 @@ typedef struct
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* this lets us disambiguate alignment padding bytes from the start of an
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* unaligned datum. (We now *require* pad bytes to be filled with zero!)
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*
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* In TOAST datums the tag field in varattrib_1b_e is used to discern whether
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* its an indirection pointer or more commonly an on-disk tuple.
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* In TOAST pointers the va_tag field (see varattrib_1b_e) is used to discern
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* the specific type and length of the pointer datum.
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*/
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/*
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