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-rw-r--r--src/include/access/detoast.h82
1 files changed, 82 insertions, 0 deletions
diff --git a/src/include/access/detoast.h b/src/include/access/detoast.h
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+++ b/src/include/access/detoast.h
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+/*-------------------------------------------------------------------------
+ *
+ * detoast.h
+ * Access to compressed and external varlena values.
+ *
+ * Copyright (c) 2000-2021, PostgreSQL Global Development Group
+ *
+ * src/include/access/detoast.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DETOAST_H
+#define DETOAST_H
+
+/*
+ * Macro to fetch the possibly-unaligned contents of an EXTERNAL datum
+ * into a local "struct varatt_external" toast pointer. This should be
+ * just a memcpy, but some versions of gcc seem to produce broken code
+ * that assumes the datum contents are aligned. Introducing an explicit
+ * intermediate "varattrib_1b_e *" variable seems to fix it.
+ */
+#define VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr) \
+do { \
+ varattrib_1b_e *attre = (varattrib_1b_e *) (attr); \
+ Assert(VARATT_IS_EXTERNAL(attre)); \
+ Assert(VARSIZE_EXTERNAL(attre) == sizeof(toast_pointer) + VARHDRSZ_EXTERNAL); \
+ memcpy(&(toast_pointer), VARDATA_EXTERNAL(attre), sizeof(toast_pointer)); \
+} while (0)
+
+/* Size of an EXTERNAL datum that contains a standard TOAST pointer */
+#define TOAST_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_external))
+
+/* Size of an EXTERNAL datum that contains an indirection pointer */
+#define INDIRECT_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_indirect))
+
+/* ----------
+ * detoast_external_attr() -
+ *
+ * Fetches an external stored attribute from the toast
+ * relation. Does NOT decompress it, if stored external
+ * in compressed format.
+ * ----------
+ */
+extern struct varlena *detoast_external_attr(struct varlena *attr);
+
+/* ----------
+ * detoast_attr() -
+ *
+ * Fully detoasts one attribute, fetching and/or decompressing
+ * it as needed.
+ * ----------
+ */
+extern struct varlena *detoast_attr(struct varlena *attr);
+
+/* ----------
+ * detoast_attr_slice() -
+ *
+ * Fetches only the specified portion of an attribute.
+ * (Handles all cases for attribute storage)
+ * ----------
+ */
+extern struct varlena *detoast_attr_slice(struct varlena *attr,
+ int32 sliceoffset,
+ int32 slicelength);
+
+/* ----------
+ * toast_raw_datum_size -
+ *
+ * Return the raw (detoasted) size of a varlena datum
+ * ----------
+ */
+extern Size toast_raw_datum_size(Datum value);
+
+/* ----------
+ * toast_datum_size -
+ *
+ * Return the storage size of a varlena datum
+ * ----------
+ */
+extern Size toast_datum_size(Datum value);
+
+#endif /* DETOAST_H */