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Create an API for inserting and deleting rows in TOAST tables.
This moves much of the non-heap-specific logic from toast_delete and toast_insert_or_update into a helper functions accessible via a new header, toast_helper.h. Using the functions in this module, a table AM can implement creation and deletion of TOAST table rows with much less code duplication than was possible heretofore. Some table AMs won't want to use the TOAST logic at all, but for those that do this will make that easier. Patch by me, reviewed and tested by Prabhat Sabu, Thomas Munro, Andres Freund, and Álvaro Herrera. Discussion: http://postgr.es/m/CA+TgmoZv-=2iWM4jcw5ZhJeL18HF96+W1yJeYrnGMYdkFFnEpQ@mail.gmail.com
This commit is contained in:
Robert Haas
@@ -12,6 +12,6 @@ subdir = src/backend/access/table
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top_builddir = ../../../..
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include $(top_builddir)/src/Makefile.global
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OBJS = table.o tableam.o tableamapi.o
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OBJS = table.o tableam.o tableamapi.o toast_helper.o
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include $(top_srcdir)/src/backend/common.mk
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331
src/backend/access/table/toast_helper.c
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331
src/backend/access/table/toast_helper.c
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@@ -0,0 +1,331 @@
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/*-------------------------------------------------------------------------
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*
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* toast_helper.c
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* Helper functions for table AMs implementing compressed or
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* out-of-line storage of varlena attributes.
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*
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* Copyright (c) 2000-2019, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/backend/access/common/toast_helper.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/detoast.h"
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#include "access/table.h"
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#include "access/toast_helper.h"
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#include "access/toast_internals.h"
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/*
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* Prepare to TOAST a tuple.
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*
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* tupleDesc, toast_values, and toast_isnull are required parameters; they
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* provide the necessary details about the tuple to be toasted.
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*
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* toast_oldvalues and toast_oldisnull should be NULL for a newly-inserted
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* tuple; for an update, they should describe the existing tuple.
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*
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* All of these arrays should have a length equal to tupleDesc->natts.
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*
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* On return, toast_flags and toast_attr will have been initialized.
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* toast_flags is just a single uint8, but toast_attr is an caller-provided
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* array with a length equal to tupleDesc->natts. The caller need not
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* perform any initialization of the array before calling this function.
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*/
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void
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toast_tuple_init(ToastTupleContext *ttc)
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{
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TupleDesc tupleDesc = ttc->ttc_rel->rd_att;
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int numAttrs = tupleDesc->natts;
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int i;
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ttc->ttc_flags = 0;
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for (i = 0; i < numAttrs; i++)
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{
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Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
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struct varlena *old_value;
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struct varlena *new_value;
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ttc->ttc_attr[i].tai_colflags = 0;
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ttc->ttc_attr[i].tai_oldexternal = NULL;
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if (ttc->ttc_oldvalues != NULL)
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{
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/*
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* For UPDATE get the old and new values of this attribute
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*/
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old_value =
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(struct varlena *) DatumGetPointer(ttc->ttc_oldvalues[i]);
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new_value =
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(struct varlena *) DatumGetPointer(ttc->ttc_values[i]);
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/*
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* If the old value is stored on disk, check if it has changed so
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* we have to delete it later.
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*/
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if (att->attlen == -1 && !ttc->ttc_oldisnull[i] &&
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VARATT_IS_EXTERNAL_ONDISK(old_value))
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{
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if (ttc->ttc_isnull[i] ||
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!VARATT_IS_EXTERNAL_ONDISK(new_value) ||
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memcmp((char *) old_value, (char *) new_value,
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VARSIZE_EXTERNAL(old_value)) != 0)
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{
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/*
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* The old external stored value isn't needed any more
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* after the update
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*/
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ttc->ttc_attr[i].tai_colflags |= TOASTCOL_NEEDS_DELETE_OLD;
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ttc->ttc_flags |= TOAST_NEEDS_DELETE_OLD;
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}
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else
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{
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/*
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* This attribute isn't changed by this update so we reuse
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* the original reference to the old value in the new
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* tuple.
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*/
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ttc->ttc_attr[i].tai_colflags |= TOASTCOL_IGNORE;
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continue;
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}
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}
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}
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else
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{
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/*
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* For INSERT simply get the new value
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*/
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new_value = (struct varlena *) DatumGetPointer(ttc->ttc_values[i]);
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}
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/*
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* Handle NULL attributes
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*/
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if (ttc->ttc_isnull[i])
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{
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ttc->ttc_attr[i].tai_colflags |= TOASTCOL_IGNORE;
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ttc->ttc_flags |= TOAST_HAS_NULLS;
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continue;
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}
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/*
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* Now look at varlena attributes
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*/
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if (att->attlen == -1)
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{
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/*
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* If the table's attribute says PLAIN always, force it so.
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*/
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if (att->attstorage == 'p')
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ttc->ttc_attr[i].tai_colflags |= TOASTCOL_IGNORE;
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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 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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*/
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if (VARATT_IS_EXTERNAL(new_value))
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{
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ttc->ttc_attr[i].tai_oldexternal = new_value;
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if (att->attstorage == 'p')
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new_value = heap_tuple_untoast_attr(new_value);
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else
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new_value = heap_tuple_fetch_attr(new_value);
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ttc->ttc_values[i] = PointerGetDatum(new_value);
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ttc->ttc_attr[i].tai_colflags |= TOASTCOL_NEEDS_FREE;
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ttc->ttc_flags |= (TOAST_NEEDS_CHANGE | TOAST_NEEDS_FREE);
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}
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/*
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* Remember the size of this attribute
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*/
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ttc->ttc_attr[i].tai_size = VARSIZE_ANY(new_value);
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}
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else
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{
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/*
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* Not a varlena attribute, plain storage always
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*/
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ttc->ttc_attr[i].tai_colflags |= TOASTCOL_IGNORE;
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}
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}
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}
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/*
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* Find the largest varlena attribute that satisfies certain criteria.
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*
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* The relevant column must not be marked TOASTCOL_IGNORE, and if the
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* for_compression flag is passed as true, it must also not be marked
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* TOASTCOL_INCOMPRESSIBLE.
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*
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* The column must have attstorage 'e' or 'x' if check_main is false, and
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* must have attstorage 'm' if check_main is true.
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*
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* The column must have a minimum size of MAXALIGN(TOAST_POINTER_SIZE);
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* if not, no benefit is to be expected by compressing it.
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*
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* The return value is the index of the biggest suitable column, or
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* -1 if there is none.
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*/
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int
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toast_tuple_find_biggest_attribute(ToastTupleContext *ttc,
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bool for_compression, bool check_main)
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{
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TupleDesc tupleDesc = ttc->ttc_rel->rd_att;
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int numAttrs = tupleDesc->natts;
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int biggest_attno = -1;
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int32 biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
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int32 skip_colflags = TOASTCOL_IGNORE;
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int i;
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if (for_compression)
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skip_colflags |= TOASTCOL_INCOMPRESSIBLE;
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for (i = 0; i < numAttrs; i++)
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{
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Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
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if ((ttc->ttc_attr[i].tai_colflags & skip_colflags) != 0)
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continue;
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if (VARATT_IS_EXTERNAL(DatumGetPointer(ttc->ttc_values[i])))
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continue; /* can't happen, toast_action would be 'p' */
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if (for_compression &&
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VARATT_IS_COMPRESSED(DatumGetPointer(ttc->ttc_values[i])))
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continue;
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if (check_main && att->attstorage != 'm')
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continue;
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if (!check_main && att->attstorage != 'x' && att->attstorage != 'e')
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continue;
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if (ttc->ttc_attr[i].tai_size > biggest_size)
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{
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biggest_attno = i;
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biggest_size = ttc->ttc_attr[i].tai_size;
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}
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}
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return biggest_attno;
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}
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/*
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* Try compression for an attribute.
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*
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* If we find that the attribute is not compressible, mark it so.
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*/
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void
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toast_tuple_try_compression(ToastTupleContext *ttc, int attribute)
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{
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Datum *value = &ttc->ttc_values[attribute];
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Datum new_value = toast_compress_datum(*value);
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ToastAttrInfo *attr = &ttc->ttc_attr[attribute];
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if (DatumGetPointer(new_value) != NULL)
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{
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/* successful compression */
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if ((attr->tai_colflags & TOASTCOL_NEEDS_FREE) != 0)
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pfree(DatumGetPointer(*value));
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*value = new_value;
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attr->tai_colflags |= TOASTCOL_NEEDS_FREE;
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attr->tai_size = VARSIZE(DatumGetPointer(*value));
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ttc->ttc_flags |= (TOAST_NEEDS_CHANGE | TOAST_NEEDS_FREE);
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}
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else
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{
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/* incompressible, ignore on subsequent compression passes */
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attr->tai_colflags |= TOASTCOL_INCOMPRESSIBLE;
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}
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}
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/*
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* Move an attribute to external storage.
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*/
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void
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toast_tuple_externalize(ToastTupleContext *ttc, int attribute, int options)
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{
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Datum *value = &ttc->ttc_values[attribute];
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Datum old_value = *value;
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ToastAttrInfo *attr = &ttc->ttc_attr[attribute];
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attr->tai_colflags |= TOASTCOL_IGNORE;
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*value = toast_save_datum(ttc->ttc_rel, old_value, attr->tai_oldexternal,
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options);
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if ((attr->tai_colflags & TOASTCOL_NEEDS_FREE) != 0)
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pfree(DatumGetPointer(old_value));
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attr->tai_colflags |= TOASTCOL_NEEDS_FREE;
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ttc->ttc_flags |= (TOAST_NEEDS_CHANGE | TOAST_NEEDS_FREE);
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}
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/*
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* Perform appropriate cleanup after one tuple has been subjected to TOAST.
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*/
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void
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toast_tuple_cleanup(ToastTupleContext *ttc)
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{
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TupleDesc tupleDesc = ttc->ttc_rel->rd_att;
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int numAttrs = tupleDesc->natts;
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/*
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* Free allocated temp values
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*/
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if ((ttc->ttc_flags & TOAST_NEEDS_FREE) != 0)
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{
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int i;
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for (i = 0; i < numAttrs; i++)
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{
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ToastAttrInfo *attr = &ttc->ttc_attr[i];
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if ((attr->tai_colflags & TOASTCOL_NEEDS_FREE) != 0)
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pfree(DatumGetPointer(ttc->ttc_values[i]));
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}
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}
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/*
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* Delete external values from the old tuple
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*/
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if ((ttc->ttc_flags & TOAST_NEEDS_DELETE_OLD) != 0)
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{
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int i;
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for (i = 0; i < numAttrs; i++)
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{
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ToastAttrInfo *attr = &ttc->ttc_attr[i];
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if ((attr->tai_colflags & TOASTCOL_NEEDS_DELETE_OLD) != 0)
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toast_delete_datum(ttc->ttc_rel, ttc->ttc_oldvalues[i], false);
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}
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}
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}
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/*
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* Check for external stored attributes and delete them from the secondary
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* relation.
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*/
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void
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toast_delete_external(Relation rel, Datum *values, bool *isnull,
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bool is_speculative)
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{
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TupleDesc tupleDesc = rel->rd_att;
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int numAttrs = tupleDesc->natts;
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int i;
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for (i = 0; i < numAttrs; i++)
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{
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if (TupleDescAttr(tupleDesc, i)->attlen == -1)
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{
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Datum value = values[i];
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if (isnull[i])
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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, is_speculative);
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}
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}
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}
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