Hi John,
> >> Also, I don't think
> >> the new logic for the ctrl/c variables is an improvement:
> >>
> >> 1. iter->ctrlc is intialized with '8' (even in the uncompressed case,
> >> which is confusing). Any time you initialize with something not 0 or
> >> 1, it's a magic number, and here it's far from where the loop variable
> >> is used. This is harder to read.
> >
> > `iter->ctrlc` is used to record the value of `ctrl` in pglz_decompress
> at the end of
> > the last iteration(or loop). In the pglz_decompress, `ctrlc`’s valid
> value is 0~7,
> > When `ctrlc` reaches 8, a control byte is read from the source
> > buffer to `ctrl` then set `ctrlc` to 0. And a control bytes should be
> read from the
> > source buffer to `ctrlc` on the first iteration. So `iter->ctrlc` should
> be intialized with '8'.
>
> My point here is it looks strange out of context, but "0" looked
> normal. Maybe a comment in init_detoast_buffer(), something like "8
> means read a control byte from the source buffer on the first
> iteration, see pg_lzdecompress_iterate()".
>
> Or, possibly, we could have a macro like INVALID_CTRLC. That might
> even improve the readability of the original function. This is just an
> idea, and maybe others would disagree, so you don't need to change it
> for now.
>
All in all, the idea is much better than a magic number 8. So, I've
implemented it.
> At this point, there are no functional things that I think we need to
> change. It's close to ready-for-committer. For the next version, I'd
> like you go through the comments and edit for grammar, spelling, and
> clarity as you see fit. I know you're not a native speaker of English,
> so I can help you with anything that remains.
I've tried my best to improve the comments, but there should be room for
further improvement
I hope you can help me perfect it.
> Also note we use braces
> on their own lines
> {
> like this
> }
>
> Done.
--
Best regards,
Binguo Bao
From 13648adb56b96a75910bb5d0a8e21d358b266d51 Mon Sep 17 00:00:00 2001
From: BBG <[email protected]>
Date: Tue, 4 Jun 2019 22:56:42 +0800
Subject: [PATCH] de-TOASTing using a iterator
---
src/backend/access/heap/tuptoaster.c | 470 +++++++++++++++++++++++++++++++++++
src/backend/utils/adt/varlena.c | 40 ++-
src/include/access/tuptoaster.h | 97 ++++++++
src/include/fmgr.h | 7 +
4 files changed, 608 insertions(+), 6 deletions(-)
diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c
index 74233bb..a8924f1 100644
--- a/src/backend/access/heap/tuptoaster.c
+++ b/src/backend/access/heap/tuptoaster.c
@@ -83,6 +83,13 @@ static int toast_open_indexes(Relation toastrel,
static void toast_close_indexes(Relation *toastidxs, int num_indexes,
LOCKMODE lock);
static void init_toast_snapshot(Snapshot toast_snapshot);
+static FetchDatumIterator create_fetch_datum_iterator(struct varlena *attr);
+static bool free_fetch_datum_iterator(FetchDatumIterator iter);
+static void fetch_datum_iterate(FetchDatumIterator iter);
+static void init_toast_buffer(ToastBuffer *buf, int size, bool compressed);
+static bool free_toast_buffer(ToastBuffer *buf);
+static void pglz_decompress_iterate(ToastBuffer *source, ToastBuffer *dest,
+ DetoastIterator iter);
/* ----------
@@ -347,6 +354,125 @@ heap_tuple_untoast_attr_slice(struct varlena *attr,
/* ----------
+ * init_detoast_iterator -
+ *
+ * The "iterator" variable is normally just a local variable in the caller.
+ * It only make sense to initialize de-TOAST iterator for external on-disk value.
+ *
+ * ----------
+ */
+bool init_detoast_iterator(struct varlena *attr, DetoastIterator iterator)
+{
+ struct varatt_external toast_pointer;
+ if (VARATT_IS_EXTERNAL_ONDISK(attr))
+ {
+ /*
+ * This is an externally stored datum --- initialize fetch datum iterator
+ */
+ iterator->fetch_datum_iterator = create_fetch_datum_iterator(attr);
+ VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
+ if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
+ {
+ /* If it's compressed, prepare buffer for raw data */
+ iterator->buf = (ToastBuffer *) palloc0(sizeof(ToastBuffer));
+ init_toast_buffer(iterator->buf, toast_pointer.va_rawsize, false);
+ iterator->ctrl = 0;
+ iterator->ctrlc = INVALID_CTRLC;
+ iterator->compressed = true;
+ iterator->done = false;
+ }
+ else
+ {
+ iterator->buf = iterator->fetch_datum_iterator->buf;
+ iterator->ctrl = 0;
+ iterator->ctrlc = INVALID_CTRLC;
+ iterator->compressed = false;
+ iterator->done = false;
+ }
+ return true;
+ }
+ else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
+ {
+ /*
+ * This is an indirect pointer --- dereference it
+ */
+ struct varatt_indirect redirect;
+
+ VARATT_EXTERNAL_GET_POINTER(redirect, attr);
+ attr = (struct varlena *) redirect.pointer;
+
+ /* nested indirect Datums aren't allowed */
+ Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));
+
+ /* recurse in case value is still extended in some other way */
+ return init_detoast_iterator(attr, iterator);
+
+ }
+ else if (VARATT_IS_COMPRESSED(attr))
+ {
+ /*
+ * This is a compressed value inside of the main tuple
+ * skip the iterator and just decompress the whole thing.
+ */
+ return false;
+ }
+
+ return false;
+}
+
+
+/* ----------
+ * free_detoast_iterator -
+ *
+ * Free the memory space occupied by the de-TOAST iterator include buffers and
+ * fetch datum iterator.
+ *
+ * Note: "iter" variable is normally just a local variable in the caller, so
+ * shouldn't free de-TOAST iterator itself.
+ * ----------
+ */
+bool free_detoast_iterator(DetoastIterator iter)
+{
+ if (iter == NULL)
+ {
+ return false;
+ }
+ if (iter->buf != iter->fetch_datum_iterator->buf)
+ {
+ free_toast_buffer(iter->buf);
+ }
+ free_fetch_datum_iterator(iter->fetch_datum_iterator);
+ return true;
+}
+
+
+/* ----------
+ * detoast_iterate -
+ *
+ * Iterate through the toasted value referenced by iterator.
+ *
+ * As long as there is another data chunk in compression or external storage,
+ * de-TOAST it into toast buffer in iterator.
+ * ----------
+ */
+extern void detoast_iterate(DetoastIterator iter)
+{
+ FetchDatumIterator fetch_iter = iter->fetch_datum_iterator;
+
+ Assert(iter != NULL && !iter->done);
+
+ fetch_datum_iterate(fetch_iter);
+
+ if (iter->compressed)
+ pglz_decompress_iterate(fetch_iter->buf, iter->buf, iter);
+
+ if (iter->buf->limit == iter->buf->capacity) {
+ iter->done = true;
+ }
+}
+
+
+/* ----------
* toast_raw_datum_size -
*
* Return the raw (detoasted) size of a varlena datum
@@ -2419,3 +2545,347 @@ init_toast_snapshot(Snapshot toast_snapshot)
InitToastSnapshot(*toast_snapshot, snapshot->lsn, snapshot->whenTaken);
}
+
+
+/* ----------
+ * create_fetch_datum_iterator -
+ *
+ * Initialize fetch datum iterator.
+ * ----------
+ */
+static FetchDatumIterator
+create_fetch_datum_iterator(struct varlena *attr)
+{
+ int validIndex;
+ FetchDatumIterator iterator;
+
+ if (!VARATT_IS_EXTERNAL_ONDISK(attr))
+ elog(ERROR, "create_fetch_datum_itearator shouldn't be called for non-ondisk datums");
+
+ iterator = (FetchDatumIterator) palloc0(sizeof(FetchDatumIteratorData));
+
+ /* Must copy to access aligned fields */
+ VARATT_EXTERNAL_GET_POINTER(iterator->toast_pointer, attr);
+
+ iterator->ressize = iterator->toast_pointer.va_extsize;
+ iterator->numchunks = ((iterator->ressize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
+
+ /*
+ * Open the toast relation and its indexes
+ */
+ iterator->toastrel = table_open(iterator->toast_pointer.va_toastrelid, AccessShareLock);
+
+ /* Look for the valid index of the toast relation */
+ validIndex = toast_open_indexes(iterator->toastrel,
+ AccessShareLock,
+ &iterator->toastidxs,
+ &iterator->num_indexes);
+
+ /*
+ * Setup a scan key to fetch from the index by va_valueid
+ */
+ ScanKeyInit(&iterator->toastkey,
+ (AttrNumber) 1,
+ BTEqualStrategyNumber, F_OIDEQ,
+ ObjectIdGetDatum(iterator->toast_pointer.va_valueid));
+
+ /*
+ * Read the chunks by index
+ *
+ * Note that because the index is actually on (valueid, chunkidx) we will
+ * see the chunks in chunkidx order, even though we didn't explicitly ask
+ * for it.
+ */
+
+ init_toast_snapshot(&iterator->SnapshotToast);
+ iterator->toastscan = systable_beginscan_ordered(iterator->toastrel, iterator->toastidxs[validIndex],
+ &iterator->SnapshotToast, 1, &iterator->toastkey);
+
+ iterator->buf = (ToastBuffer *) palloc0(sizeof(ToastBuffer));
+ init_toast_buffer(iterator->buf, iterator->ressize + VARHDRSZ, VARATT_EXTERNAL_IS_COMPRESSED(iterator->toast_pointer));
+
+ iterator->nextidx = 0;
+ iterator->done = false;
+
+ return iterator;
+}
+
+static bool
+free_fetch_datum_iterator(FetchDatumIterator iter)
+{
+ if (iter == NULL)
+ {
+ return false;
+ }
+
+ if (!iter->done)
+ {
+ systable_endscan_ordered(iter->toastscan);
+ toast_close_indexes(iter->toastidxs, iter->num_indexes, AccessShareLock);
+ table_close(iter->toastrel, AccessShareLock);
+ }
+ free_toast_buffer(iter->buf);
+ pfree(iter);
+ return true;
+}
+
+/* ----------
+ * fetch_datum_iterate -
+ *
+ * Iterate through the toasted value referenced by iterator.
+ *
+ * As long as there is another chunk data in compression or external storage,
+ * fetch it into buffer in iterator.
+ * ----------
+ */
+static void
+fetch_datum_iterate(FetchDatumIterator iter)
+{
+ HeapTuple ttup;
+ TupleDesc toasttupDesc;
+ int32 residx;
+ Pointer chunk;
+ bool isnull;
+ char *chunkdata;
+ int32 chunksize;
+
+ Assert(iter != NULL && !iter->done);
+
+ ttup = systable_getnext_ordered(iter->toastscan, ForwardScanDirection);
+ if (ttup == NULL)
+ {
+ /*
+ * Final checks that we successfully fetched the datum
+ */
+ if (iter->nextidx != iter->numchunks)
+ elog(ERROR, "missing chunk number %d for toast value %u in %s",
+ iter->nextidx,
+ iter->toast_pointer.va_valueid,
+ RelationGetRelationName(iter->toastrel));
+
+ /*
+ * End scan and close relations
+ */
+ systable_endscan_ordered(iter->toastscan);
+ toast_close_indexes(iter->toastidxs, iter->num_indexes, AccessShareLock);
+ table_close(iter->toastrel, AccessShareLock);
+
+ iter->done = true;
+ return;
+ }
+
+ /*
+ * Have a chunk, extract the sequence number and the data
+ */
+ toasttupDesc = iter->toastrel->rd_att;
+ residx = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
+ Assert(!isnull);
+ chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
+ Assert(!isnull);
+ if (!VARATT_IS_EXTENDED(chunk))
+ {
+ chunksize = VARSIZE(chunk) - VARHDRSZ;
+ chunkdata = VARDATA(chunk);
+ }
+ else if (VARATT_IS_SHORT(chunk))
+ {
+ /* could happen due to heap_form_tuple doing its thing */
+ chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
+ chunkdata = VARDATA_SHORT(chunk);
+ }
+ else
+ {
+ /* should never happen */
+ elog(ERROR, "found toasted toast chunk for toast value %u in %s",
+ iter->toast_pointer.va_valueid,
+ RelationGetRelationName(iter->toastrel));
+ chunksize = 0; /* keep compiler quiet */
+ chunkdata = NULL;
+ }
+
+ /*
+ * Some checks on the data we've found
+ */
+ if (residx != iter->nextidx)
+ elog(ERROR, "unexpected chunk number %d (expected %d) for toast value %u in %s",
+ residx, iter->nextidx,
+ iter->toast_pointer.va_valueid,
+ RelationGetRelationName(iter->toastrel));
+ if (residx < iter->numchunks - 1)
+ {
+ if (chunksize != TOAST_MAX_CHUNK_SIZE)
+ elog(ERROR, "unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
+ chunksize, (int) TOAST_MAX_CHUNK_SIZE,
+ residx, iter->numchunks,
+ iter->toast_pointer.va_valueid,
+ RelationGetRelationName(iter->toastrel));
+ }
+ else if (residx == iter->numchunks - 1)
+ {
+ if ((residx * TOAST_MAX_CHUNK_SIZE + chunksize) != iter->ressize)
+ elog(ERROR, "unexpected chunk size %d (expected %d) in final chunk %d for toast value %u in %s",
+ chunksize,
+ (int) (iter->ressize - residx * TOAST_MAX_CHUNK_SIZE),
+ residx,
+ iter->toast_pointer.va_valueid,
+ RelationGetRelationName(iter->toastrel));
+ }
+ else
+ elog(ERROR, "unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
+ residx,
+ 0, iter->numchunks - 1,
+ iter->toast_pointer.va_valueid,
+ RelationGetRelationName(iter->toastrel));
+
+ /*
+ * Copy the data into proper place in our iterator buffer
+ */
+ memcpy(iter->buf->limit, chunkdata, chunksize);
+ iter->buf->limit += chunksize;
+
+ iter->nextidx++;
+}
+
+
+static void
+init_toast_buffer(ToastBuffer *buf, int32 size, bool compressed)
+{
+ buf->buf = (const char *) palloc0(size);
+ if (compressed) {
+ SET_VARSIZE_COMPRESSED(buf->buf, size);
+ /*
+ * Note the constrain buf->position <= buf->limit may be broken
+ * at initialization. Make sure that the constrain is satisfied
+ * when consume chars.
+ */
+ buf->position = VARDATA_4B_C(buf->buf);
+ }
+ else
+ {
+ SET_VARSIZE(buf->buf, size);
+ buf->position = VARDATA_4B(buf->buf);
+ }
+ buf->limit = VARDATA(buf->buf);
+ buf->capacity = buf->buf + size;
+ buf->buf_size = size;
+}
+
+
+static bool
+free_toast_buffer(ToastBuffer *buf)
+{
+ if (buf == NULL)
+ {
+ return false;
+ }
+
+ pfree((void *)buf->buf);
+ pfree(buf);
+
+ return true;
+}
+
+
+/* ----------
+ * pglz_decompress_iterate -
+ *
+ * Decompresses source into dest until the source is exhausted.
+ * ----------
+ */
+static void
+pglz_decompress_iterate(ToastBuffer *source, ToastBuffer *dest, DetoastIterator iter)
+{
+ const unsigned char *sp;
+ const unsigned char *srcend;
+ unsigned char *dp;
+ unsigned char *destend;
+
+ /*
+ * In the while loop, sp may go beyond the srcend, provides a four-byte
+ * buffer to prevent sp from reading unallocated bytes from source buffer.
+ * When source->limit reaches source->capacity, don't worry about reading
+ * unallocated bytes.
+ */
+ srcend = (const unsigned char *)
+ (source->limit == source->capacity ? source->limit : (source->limit - 4));
+ sp = (const unsigned char *) source->position;
+ dp = (unsigned char *) dest->limit;
+ destend = (unsigned char *) dest->capacity;
+
+ while (sp < srcend && dp < destend)
+ {
+ /*
+ * Read one control byte and process the next 8 items (or as many as
+ * remain in the compressed input).
+ */
+ unsigned char ctrl;
+ int ctrlc;
+
+ if (iter->ctrlc != INVALID_CTRLC)
+ {
+ ctrl = iter->ctrl;
+ ctrlc = iter->ctrlc;
+ }
+ else
+ {
+ ctrl = *sp++;
+ ctrlc = 0;
+ }
+
+
+ for (; ctrlc < 8 && sp < srcend && dp < destend; ctrlc++)
+ {
+
+ if (ctrl & 1)
+ {
+ /*
+ * Otherwise it contains the match length minus 3 and the
+ * upper 4 bits of the offset. The next following byte
+ * contains the lower 8 bits of the offset. If the length is
+ * coded as 18, another extension tag byte tells how much
+ * longer the match really was (0-255).
+ */
+ int32 len;
+ int32 off;
+
+ len = (sp[0] & 0x0f) + 3;
+ off = ((sp[0] & 0xf0) << 4) | sp[1];
+ sp += 2;
+ if (len == 18)
+ len += *sp++;
+
+ /*
+ * Now we copy the bytes specified by the tag from OUTPUT to
+ * OUTPUT. It is dangerous and platform dependent to use
+ * memcpy() here, because the copied areas could overlap
+ * extremely!
+ */
+ len = Min(len, destend - dp);
+ while (len--)
+ {
+ *dp = dp[-off];
+ dp++;
+ }
+ }
+ else
+ {
+ /*
+ * An unset control bit means LITERAL BYTE. So we just copy
+ * one from INPUT to OUTPUT.
+ */
+ *dp++ = *sp++;
+ }
+
+ /*
+ * Advance the control bit
+ */
+ ctrl >>= 1;
+ }
+
+ iter->ctrlc = ctrlc;
+ iter->ctrl = ctrl;
+ }
+
+ source->position = (char *) sp;
+ dest->limit = (char *) dp;
+}
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index fa08b55..cb63891 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -56,6 +56,8 @@ typedef struct
int len1; /* string lengths in bytes */
int len2;
+ DetoastIterator iter;
+
/* Skip table for Boyer-Moore-Horspool search algorithm: */
int skiptablemask; /* mask for ANDing with skiptable subscripts */
int skiptable[256]; /* skip distance for given mismatched char */
@@ -122,7 +124,7 @@ static text *text_substring(Datum str,
int32 length,
bool length_not_specified);
static text *text_overlay(text *t1, text *t2, int sp, int sl);
-static int text_position(text *t1, text *t2, Oid collid);
+static int text_position(text *t1, text *t2, Oid collid, DetoastIterator iter);
static void text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state);
static bool text_position_next(TextPositionState *state);
static char *text_position_next_internal(char *start_ptr, TextPositionState *state);
@@ -1092,10 +1094,22 @@ text_overlay(text *t1, text *t2, int sp, int sl)
Datum
textpos(PG_FUNCTION_ARGS)
{
- text *str = PG_GETARG_TEXT_PP(0);
+ text *str;
+ DetoastIteratorData iteratorData;
+ DetoastIterator iter = &iteratorData;
text *search_str = PG_GETARG_TEXT_PP(1);
- PG_RETURN_INT32((int32) text_position(str, search_str, PG_GET_COLLATION()));
+ if (init_detoast_iterator((struct varlena *) (DatumGetPointer(PG_GETARG_DATUM(0))), iter))
+ {
+ str = (text *) iter->buf->buf;
+ }
+ else
+ {
+ str = PG_GETARG_TEXT_PP(0);
+ iter = NULL;
+ }
+
+ PG_RETURN_INT32((int32) text_position(str, search_str, PG_GET_COLLATION(), iter));
}
/*
@@ -1113,7 +1127,7 @@ textpos(PG_FUNCTION_ARGS)
* functions.
*/
static int
-text_position(text *t1, text *t2, Oid collid)
+text_position(text *t1, text *t2, Oid collid, DetoastIterator iter)
{
TextPositionState state;
int result;
@@ -1122,6 +1136,7 @@ text_position(text *t1, text *t2, Oid collid)
return 0;
text_position_setup(t1, t2, collid, &state);
+ state.iter = iter;
if (!text_position_next(&state))
result = 0;
else
@@ -1130,7 +1145,6 @@ text_position(text *t1, text *t2, Oid collid)
return result;
}
-
/*
* text_position_setup, text_position_next, text_position_cleanup -
* Component steps of text_position()
@@ -1196,6 +1210,7 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
state->str2 = VARDATA_ANY(t2);
state->len1 = len1;
state->len2 = len2;
+ state->iter = NULL;
state->last_match = NULL;
state->refpoint = state->str1;
state->refpos = 0;
@@ -1358,6 +1373,11 @@ text_position_next_internal(char *start_ptr, TextPositionState *state)
hptr = start_ptr;
while (hptr < haystack_end)
{
+ if (state->iter != NULL)
+ {
+ PG_DETOAST_ITERATE(state->iter, hptr);
+ }
+
if (*hptr == nchar)
return (char *) hptr;
hptr++;
@@ -1375,6 +1395,11 @@ text_position_next_internal(char *start_ptr, TextPositionState *state)
const char *nptr;
const char *p;
+ if (state->iter != NULL)
+ {
+ PG_DETOAST_ITERATE(state->iter, hptr);
+ }
+
nptr = needle_last;
p = hptr;
while (*nptr == *p)
@@ -1438,7 +1463,10 @@ text_position_get_match_pos(TextPositionState *state)
static void
text_position_cleanup(TextPositionState *state)
{
- /* no cleanup needed */
+ if (state->iter != NULL)
+ {
+ free_detoast_iterator(state->iter);
+ }
}
static void
diff --git a/src/include/access/tuptoaster.h b/src/include/access/tuptoaster.h
index f0aea24..79fd4c4 100644
--- a/src/include/access/tuptoaster.h
+++ b/src/include/access/tuptoaster.h
@@ -17,6 +17,103 @@
#include "storage/lockdefs.h"
#include "utils/relcache.h"
+#ifndef FRONTEND
+#include "access/genam.h"
+
+/*
+ * TOAST buffer is a producer consumer buffer.
+ *
+ * +--+--+--+--+--+--+--+--+--+--+--+--+--+
+ * | | | | | | | | | | | | | |
+ * +--+--+--+--+--+--+--+--+--+--+--+--+--+
+ * ^ ^ ^ ^
+ * buf position limit capacity
+ *
+ * buf: point to the start of buffer.
+ * position: point to the next char to be consumed.
+ * limit: point to the next char to be produced.
+ * capacity: point to the end of buffer.
+ *
+ * Constrains that need to be satisfied:
+ * buf <= position <= limit <= capacity
+ */
+typedef struct ToastBuffer
+{
+ const char *buf;
+ const char *position;
+ char *limit;
+ const char *capacity;
+ int32 buf_size;
+} ToastBuffer;
+
+
+typedef struct FetchDatumIteratorData
+{
+ ToastBuffer *buf;
+ Relation toastrel;
+ Relation *toastidxs;
+ SysScanDesc toastscan;
+ ScanKeyData toastkey;
+ SnapshotData SnapshotToast;
+ struct varatt_external toast_pointer;
+ int32 ressize;
+ int32 nextidx;
+ int32 numchunks;
+ int num_indexes;
+ bool done;
+} FetchDatumIteratorData;
+
+typedef struct FetchDatumIteratorData *FetchDatumIterator;
+
+/*
+ * If "ctrlc" field in iterator is equal to INVALID_CTRLC, it means that
+ * the field is invalid and need to read the control byte from the
+ * source buffer in the next iteration, see pglz_decompress_iterate().
+ */
+#define INVALID_CTRLC 8
+
+typedef struct DetoastIteratorData
+{
+ ToastBuffer *buf;
+ FetchDatumIterator fetch_datum_iterator;
+ unsigned char ctrl;
+ int ctrlc;
+ bool compressed; /* toast value is compressed? */
+ bool done;
+} DetoastIteratorData;
+
+typedef struct DetoastIteratorData *DetoastIterator;
+
+/* ----------
+ * init_detoast_iterator -
+ *
+ * Initialize de-TOAST iterator.
+ * ----------
+ */
+extern bool init_detoast_iterator(struct varlena *attr, DetoastIterator iterator);
+
+/* ----------
+ * free_detoast_iterator -
+ *
+ * Free the memory space occupied by the de-TOAST iterator.
+ * ----------
+ */
+extern bool free_detoast_iterator(DetoastIterator iter);
+
+/* ----------
+ * detoast_iterate -
+ *
+ * Iterate through the toasted value referenced by iterator.
+ *
+ * As long as there is another slice in compression or external storage,
+ * de-TOAST it into buffer in iterator.
+ * ----------
+ */
+extern void detoast_iterate(DetoastIterator iter);
+
+#endif
+
+
/*
* This enables de-toasting of index entries. Needed until VACUUM is
* smart enough to rebuild indexes from scratch.
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 3ff0999..446c880 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -239,6 +239,13 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena *datum);
#define PG_DETOAST_DATUM_SLICE(datum,f,c) \
pg_detoast_datum_slice((struct varlena *) DatumGetPointer(datum), \
(int32) (f), (int32) (c))
+#define PG_DETOAST_ITERATE(iter, need) \
+ do { \
+ Assert(need >= iter->buf->buf && need <= iter->buf->capacity); \
+ while (!iter->done && need >= iter->buf->limit) { \
+ detoast_iterate(iter); \
+ } \
+ } while (0)
/* WARNING -- unaligned pointer */
#define PG_DETOAST_DATUM_PACKED(datum) \
pg_detoast_datum_packed((struct varlena *) DatumGetPointer(datum))
--
2.7.4
