|
| 1 | +/*------------------------------------------------------------------------- |
| 2 | + * |
| 3 | + * detoast.c |
| 4 | + * Retrieve compressed or external variable size attributes. |
| 5 | + * |
| 6 | + * Copyright (c) 2000-2022, PostgreSQL Global Development Group |
| 7 | + * |
| 8 | + * IDENTIFICATION |
| 9 | + * src/backend/access/common/detoast.c |
| 10 | + * |
| 11 | + *------------------------------------------------------------------------- |
| 12 | + */ |
| 13 | + |
| 14 | +#include "postgres.h" |
| 15 | + |
| 16 | +#include "access/detoast.h" |
| 17 | +#include "access/table.h" |
| 18 | +#include "access/tableam.h" |
| 19 | +#include "access/toast_internals.h" |
| 20 | +#include "common/int.h" |
| 21 | +#include "common/pg_lzcompress.h" |
| 22 | +#include "utils/expandeddatum.h" |
| 23 | +#include "utils/rel.h" |
| 24 | +#include "access/toasterapi.h" |
| 25 | + |
| 26 | +/* ---------- |
| 27 | + * create_detoast_iterator - |
| 28 | + * |
| 29 | + * It only makes sense to initialize a de-TOAST iterator for external on-disk values. |
| 30 | + * |
| 31 | + * ---------- |
| 32 | + */ |
| 33 | +DetoastIterator |
| 34 | +create_detoast_iterator(struct varlena *attr) |
| 35 | +{ |
| 36 | + struct varatt_external toast_pointer; |
| 37 | + DetoastIterator iter; |
| 38 | + if (VARATT_IS_EXTERNAL_ONDISK(attr)) |
| 39 | + { |
| 40 | + FetchDatumIterator fetch_iter; |
| 41 | + |
| 42 | + iter = (DetoastIterator) palloc0(sizeof(DetoastIteratorData)); |
| 43 | + iter->done = false; |
| 44 | + iter->nrefs = 1; |
| 45 | + |
| 46 | + /* This is an externally stored datum --- initialize fetch datum iterator */ |
| 47 | + iter->fetch_datum_iterator = fetch_iter = create_fetch_datum_iterator(attr); |
| 48 | + VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr); |
| 49 | + if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer)) |
| 50 | + { |
| 51 | + iter->compressed = true; |
| 52 | + |
| 53 | + /* prepare buffer to received decompressed data */ |
| 54 | + iter->buf = create_toast_buffer(toast_pointer.va_rawsize, false); |
| 55 | + |
| 56 | + /* initialize state for pglz_decompress_iterate() */ |
| 57 | + iter->ctrl = 0; |
| 58 | + iter->ctrlc = INVALID_CTRLC; |
| 59 | + } |
| 60 | + else |
| 61 | + { |
| 62 | + iter->compressed = false; |
| 63 | + |
| 64 | + /* point the buffer directly at the raw data */ |
| 65 | + iter->buf = fetch_iter->buf; |
| 66 | + } |
| 67 | + return iter; |
| 68 | + } |
| 69 | + else if (VARATT_IS_EXTERNAL_INDIRECT(attr)) |
| 70 | + { |
| 71 | + /* indirect pointer --- dereference it */ |
| 72 | + struct varatt_indirect redirect; |
| 73 | + |
| 74 | + VARATT_EXTERNAL_GET_POINTER(redirect, attr); |
| 75 | + attr = (struct varlena *) redirect.pointer; |
| 76 | + |
| 77 | + /* nested indirect Datums aren't allowed */ |
| 78 | + Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr)); |
| 79 | + |
| 80 | + /* recurse in case value is still extended in some other way */ |
| 81 | + return create_detoast_iterator(attr); |
| 82 | + |
| 83 | + } |
| 84 | + else if (VARATT_IS_COMPRESSED(attr)) |
| 85 | + { |
| 86 | + ToastBuffer *buf; |
| 87 | + |
| 88 | + iter = (DetoastIterator) palloc0(sizeof(DetoastIteratorData)); |
| 89 | + iter->done = false; |
| 90 | + iter->nrefs = 1; |
| 91 | + |
| 92 | + iter->fetch_datum_iterator = palloc0(sizeof(*iter->fetch_datum_iterator)); |
| 93 | + iter->fetch_datum_iterator->buf = buf = create_toast_buffer(VARSIZE_ANY(attr), true); |
| 94 | + iter->fetch_datum_iterator->done = true; |
| 95 | + iter->compressed = true; |
| 96 | + |
| 97 | + memcpy((void *) buf->buf, attr, VARSIZE_ANY(attr)); |
| 98 | + buf->limit = (char *) buf->capacity; |
| 99 | + |
| 100 | + /* prepare buffer to received decompressed data */ |
| 101 | + iter->buf = create_toast_buffer(TOAST_COMPRESS_EXTSIZE(attr) + VARHDRSZ, false); |
| 102 | + |
| 103 | + /* initialize state for pglz_decompress_iterate() */ |
| 104 | + iter->ctrl = 0; |
| 105 | + iter->ctrlc = INVALID_CTRLC; |
| 106 | + return iter; |
| 107 | + } |
| 108 | + else |
| 109 | + /* in-line value -- no iteration used, even if it's compressed */ |
| 110 | + return NULL; |
| 111 | +} |
| 112 | + |
| 113 | +/* ---------- |
| 114 | + * free_detoast_iterator - |
| 115 | + * |
| 116 | + * Free memory used by the de-TOAST iterator, including buffers and |
| 117 | + * fetch datum iterator. |
| 118 | + * ---------- |
| 119 | + */ |
| 120 | +void |
| 121 | +free_detoast_iterator(DetoastIterator iter) |
| 122 | +{ |
| 123 | + if (iter == NULL) |
| 124 | + return; |
| 125 | + if (--iter->nrefs > 0) |
| 126 | + return; |
| 127 | + if (iter->compressed) |
| 128 | + free_toast_buffer(iter->buf); |
| 129 | + free_fetch_datum_iterator(iter->fetch_datum_iterator); |
| 130 | + pfree(iter); |
| 131 | +} |
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