831 lines
27 KiB
C
831 lines
27 KiB
C
/*-------------------------------------------------------------------------
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*
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* nbtdedup.c
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* Deduplicate items in Postgres btrees.
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/access/nbtree/nbtdedup.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/nbtree.h"
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#include "access/nbtxlog.h"
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#include "miscadmin.h"
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#include "utils/rel.h"
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static bool _bt_do_singleval(Relation rel, Page page, BTDedupState state,
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OffsetNumber minoff, IndexTuple newitem);
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static void _bt_singleval_fillfactor(Page page, BTDedupState state,
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Size newitemsz);
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#ifdef USE_ASSERT_CHECKING
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static bool _bt_posting_valid(IndexTuple posting);
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#endif
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/*
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* Deduplicate items on a leaf page. The page will have to be split by caller
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* if we cannot successfully free at least newitemsz (we also need space for
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* newitem's line pointer, which isn't included in caller's newitemsz).
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*
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* The general approach taken here is to perform as much deduplication as
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* possible to free as much space as possible. Note, however, that "single
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* value" strategy is sometimes used for !checkingunique callers, in which
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* case deduplication will leave a few tuples untouched at the end of the
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* page. The general idea is to prepare the page for an anticipated page
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* split that uses nbtsplitloc.c's "single value" strategy to determine a
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* split point. (There is no reason to deduplicate items that will end up on
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* the right half of the page after the anticipated page split; better to
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* handle those if and when the anticipated right half page gets its own
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* deduplication pass, following further inserts of duplicates.)
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*
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* This function should be called during insertion, when the page doesn't have
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* enough space to fit an incoming newitem. If the BTP_HAS_GARBAGE page flag
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* was set, caller should have removed any LP_DEAD items by calling
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* _bt_vacuum_one_page() before calling here. We may still have to kill
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* LP_DEAD items here when the page's BTP_HAS_GARBAGE hint is falsely unset,
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* but that should be rare. Also, _bt_vacuum_one_page() won't unset the
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* BTP_HAS_GARBAGE flag when it finds no LP_DEAD items, so a successful
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* deduplication pass will always clear it, just to keep things tidy.
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*/
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void
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_bt_dedup_one_page(Relation rel, Buffer buf, Relation heapRel,
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IndexTuple newitem, Size newitemsz, bool checkingunique)
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{
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OffsetNumber offnum,
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minoff,
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maxoff;
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Page page = BufferGetPage(buf);
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BTPageOpaque opaque;
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Page newpage;
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int newpagendataitems = 0;
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OffsetNumber deletable[MaxIndexTuplesPerPage];
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BTDedupState state;
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int ndeletable = 0;
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Size pagesaving = 0;
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bool singlevalstrat = false;
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int natts = IndexRelationGetNumberOfAttributes(rel);
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/*
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* We can't assume that there are no LP_DEAD items. For one thing, VACUUM
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* will clear the BTP_HAS_GARBAGE hint without reliably removing items
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* that are marked LP_DEAD. We don't want to unnecessarily unset LP_DEAD
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* bits when deduplicating items. Allowing it would be correct, though
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* wasteful.
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*/
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opaque = (BTPageOpaque) PageGetSpecialPointer(page);
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minoff = P_FIRSTDATAKEY(opaque);
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maxoff = PageGetMaxOffsetNumber(page);
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for (offnum = minoff;
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offnum <= maxoff;
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offnum = OffsetNumberNext(offnum))
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{
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ItemId itemid = PageGetItemId(page, offnum);
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if (ItemIdIsDead(itemid))
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deletable[ndeletable++] = offnum;
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}
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if (ndeletable > 0)
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{
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_bt_delitems_delete(rel, buf, deletable, ndeletable, heapRel);
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/*
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* Return when a split will be avoided. This is equivalent to
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* avoiding a split using the usual _bt_vacuum_one_page() path.
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*/
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if (PageGetFreeSpace(page) >= newitemsz)
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return;
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/*
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* Reconsider number of items on page, in case _bt_delitems_delete()
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* managed to delete an item or two
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*/
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minoff = P_FIRSTDATAKEY(opaque);
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maxoff = PageGetMaxOffsetNumber(page);
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}
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/* Passed-in newitemsz is MAXALIGNED but does not include line pointer */
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newitemsz += sizeof(ItemIdData);
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/*
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* By here, it's clear that deduplication will definitely be attempted.
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* Initialize deduplication state.
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*
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* It would be possible for maxpostingsize (limit on posting list tuple
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* size) to be set to one third of the page. However, it seems like a
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* good idea to limit the size of posting lists to one sixth of a page.
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* That ought to leave us with a good split point when pages full of
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* duplicates can be split several times.
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*/
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state = (BTDedupState) palloc(sizeof(BTDedupStateData));
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state->deduplicate = true;
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state->maxpostingsize = Min(BTMaxItemSize(page) / 2, INDEX_SIZE_MASK);
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/* Metadata about base tuple of current pending posting list */
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state->base = NULL;
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state->baseoff = InvalidOffsetNumber;
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state->basetupsize = 0;
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/* Metadata about current pending posting list TIDs */
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state->htids = palloc(state->maxpostingsize);
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state->nhtids = 0;
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state->nitems = 0;
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/* Size of all physical tuples to be replaced by pending posting list */
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state->phystupsize = 0;
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/* nintervals should be initialized to zero */
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state->nintervals = 0;
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/* Determine if "single value" strategy should be used */
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if (!checkingunique)
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singlevalstrat = _bt_do_singleval(rel, page, state, minoff, newitem);
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/*
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* Deduplicate items from page, and write them to newpage.
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*
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* Copy the original page's LSN into newpage copy. This will become the
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* updated version of the page. We need this because XLogInsert will
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* examine the LSN and possibly dump it in a page image.
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*/
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newpage = PageGetTempPageCopySpecial(page);
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PageSetLSN(newpage, PageGetLSN(page));
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/* Copy high key, if any */
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if (!P_RIGHTMOST(opaque))
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{
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ItemId hitemid = PageGetItemId(page, P_HIKEY);
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Size hitemsz = ItemIdGetLength(hitemid);
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IndexTuple hitem = (IndexTuple) PageGetItem(page, hitemid);
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if (PageAddItem(newpage, (Item) hitem, hitemsz, P_HIKEY,
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false, false) == InvalidOffsetNumber)
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elog(ERROR, "deduplication failed to add highkey");
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}
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for (offnum = minoff;
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offnum <= maxoff;
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offnum = OffsetNumberNext(offnum))
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{
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ItemId itemid = PageGetItemId(page, offnum);
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IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
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Assert(!ItemIdIsDead(itemid));
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if (offnum == minoff)
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{
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/*
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* No previous/base tuple for the data item -- use the data item
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* as base tuple of pending posting list
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*/
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_bt_dedup_start_pending(state, itup, offnum);
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}
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else if (state->deduplicate &&
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_bt_keep_natts_fast(rel, state->base, itup) > natts &&
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_bt_dedup_save_htid(state, itup))
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{
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/*
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* Tuple is equal to base tuple of pending posting list. Heap
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* TID(s) for itup have been saved in state.
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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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* Tuple is not equal to pending posting list tuple, or
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* _bt_dedup_save_htid() opted to not merge current item into
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* pending posting list for some other reason (e.g., adding more
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* TIDs would have caused posting list to exceed current
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* maxpostingsize).
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*
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* If state contains pending posting list with more than one item,
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* form new posting tuple, and actually update the page. Else
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* reset the state and move on without modifying the page.
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*/
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pagesaving += _bt_dedup_finish_pending(newpage, state);
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newpagendataitems++;
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if (singlevalstrat)
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{
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/*
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* Single value strategy's extra steps.
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*
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* Lower maxpostingsize for sixth and final item that might be
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* deduplicated by current deduplication pass. When sixth
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* item formed/observed, stop deduplicating items.
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*
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* Note: It's possible that this will be reached even when
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* current deduplication pass has yet to merge together some
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* existing items. It doesn't matter whether or not the
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* current call generated the maxpostingsize-capped duplicate
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* tuples at the start of the page.
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*/
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if (newpagendataitems == 5)
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_bt_singleval_fillfactor(page, state, newitemsz);
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else if (newpagendataitems == 6)
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{
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state->deduplicate = false;
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singlevalstrat = false; /* won't be back here */
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}
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}
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/* itup starts new pending posting list */
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_bt_dedup_start_pending(state, itup, offnum);
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}
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}
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/* Handle the last item */
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pagesaving += _bt_dedup_finish_pending(newpage, state);
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newpagendataitems++;
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/*
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* If no items suitable for deduplication were found, newpage must be
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* exactly the same as the original page, so just return from function.
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*
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* We could determine whether or not to proceed on the basis the space
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* savings being sufficient to avoid an immediate page split instead. We
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* don't do that because there is some small value in nbtsplitloc.c always
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* operating against a page that is fully deduplicated (apart from
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* newitem). Besides, most of the cost has already been paid.
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*/
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if (state->nintervals == 0)
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{
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/* cannot leak memory here */
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pfree(newpage);
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pfree(state->htids);
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pfree(state);
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return;
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}
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/*
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* By here, it's clear that deduplication will definitely go ahead.
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*
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* Clear the BTP_HAS_GARBAGE page flag in the unlikely event that it is
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* still falsely set, just to keep things tidy. (We can't rely on
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* _bt_vacuum_one_page() having done this already, and we can't rely on a
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* page split or VACUUM getting to it in the near future.)
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*/
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if (P_HAS_GARBAGE(opaque))
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{
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BTPageOpaque nopaque = (BTPageOpaque) PageGetSpecialPointer(newpage);
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nopaque->btpo_flags &= ~BTP_HAS_GARBAGE;
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}
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START_CRIT_SECTION();
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PageRestoreTempPage(newpage, page);
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MarkBufferDirty(buf);
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/* XLOG stuff */
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if (RelationNeedsWAL(rel))
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{
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XLogRecPtr recptr;
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xl_btree_dedup xlrec_dedup;
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xlrec_dedup.nintervals = state->nintervals;
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XLogBeginInsert();
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XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
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XLogRegisterData((char *) &xlrec_dedup, SizeOfBtreeDedup);
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/*
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* The intervals array is not in the buffer, but pretend that it is.
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* When XLogInsert stores the whole buffer, the array need not be
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* stored too.
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*/
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XLogRegisterBufData(0, (char *) state->intervals,
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state->nintervals * sizeof(BTDedupInterval));
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recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DEDUP);
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PageSetLSN(page, recptr);
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}
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END_CRIT_SECTION();
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/* Local space accounting should agree with page accounting */
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Assert(pagesaving < newitemsz || PageGetExactFreeSpace(page) >= newitemsz);
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/* cannot leak memory here */
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pfree(state->htids);
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pfree(state);
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}
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/*
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* Create a new pending posting list tuple based on caller's base tuple.
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*
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* Every tuple processed by deduplication either becomes the base tuple for a
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* posting list, or gets its heap TID(s) accepted into a pending posting list.
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* A tuple that starts out as the base tuple for a posting list will only
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* actually be rewritten within _bt_dedup_finish_pending() when it turns out
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* that there are duplicates that can be merged into the base tuple.
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*/
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void
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_bt_dedup_start_pending(BTDedupState state, IndexTuple base,
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OffsetNumber baseoff)
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{
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Assert(state->nhtids == 0);
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Assert(state->nitems == 0);
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Assert(!BTreeTupleIsPivot(base));
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/*
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* Copy heap TID(s) from new base tuple for new candidate posting list
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* into working state's array
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*/
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if (!BTreeTupleIsPosting(base))
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{
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memcpy(state->htids, &base->t_tid, sizeof(ItemPointerData));
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state->nhtids = 1;
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state->basetupsize = IndexTupleSize(base);
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}
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else
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{
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int nposting;
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nposting = BTreeTupleGetNPosting(base);
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memcpy(state->htids, BTreeTupleGetPosting(base),
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sizeof(ItemPointerData) * nposting);
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state->nhtids = nposting;
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/* basetupsize should not include existing posting list */
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state->basetupsize = BTreeTupleGetPostingOffset(base);
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}
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/*
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* Save new base tuple itself -- it'll be needed if we actually create a
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* new posting list from new pending posting list.
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*
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* Must maintain physical size of all existing tuples (including line
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* pointer overhead) so that we can calculate space savings on page.
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*/
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state->nitems = 1;
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state->base = base;
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state->baseoff = baseoff;
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state->phystupsize = MAXALIGN(IndexTupleSize(base)) + sizeof(ItemIdData);
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/* Also save baseoff in pending state for interval */
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state->intervals[state->nintervals].baseoff = state->baseoff;
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}
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/*
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* Save itup heap TID(s) into pending posting list where possible.
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*
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* Returns bool indicating if the pending posting list managed by state now
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* includes itup's heap TID(s).
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*/
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bool
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_bt_dedup_save_htid(BTDedupState state, IndexTuple itup)
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{
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int nhtids;
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ItemPointer htids;
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Size mergedtupsz;
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Assert(!BTreeTupleIsPivot(itup));
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if (!BTreeTupleIsPosting(itup))
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{
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nhtids = 1;
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htids = &itup->t_tid;
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}
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else
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{
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nhtids = BTreeTupleGetNPosting(itup);
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htids = BTreeTupleGetPosting(itup);
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}
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/*
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* Don't append (have caller finish pending posting list as-is) if
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* appending heap TID(s) from itup would put us over maxpostingsize limit.
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*
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* This calculation needs to match the code used within _bt_form_posting()
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* for new posting list tuples.
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*/
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mergedtupsz = MAXALIGN(state->basetupsize +
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(state->nhtids + nhtids) * sizeof(ItemPointerData));
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if (mergedtupsz > state->maxpostingsize)
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return false;
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/*
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* Save heap TIDs to pending posting list tuple -- itup can be merged into
|
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* pending posting list
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*/
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state->nitems++;
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memcpy(state->htids + state->nhtids, htids,
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sizeof(ItemPointerData) * nhtids);
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state->nhtids += nhtids;
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state->phystupsize += MAXALIGN(IndexTupleSize(itup)) + sizeof(ItemIdData);
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return true;
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}
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/*
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* Finalize pending posting list tuple, and add it to the page. Final tuple
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* is based on saved base tuple, and saved list of heap TIDs.
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*
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* Returns space saving from deduplicating to make a new posting list tuple.
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* Note that this includes line pointer overhead. This is zero in the case
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* where no deduplication was possible.
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*/
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Size
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_bt_dedup_finish_pending(Page newpage, BTDedupState state)
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{
|
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OffsetNumber tupoff;
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Size tuplesz;
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Size spacesaving;
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|
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Assert(state->nitems > 0);
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Assert(state->nitems <= state->nhtids);
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Assert(state->intervals[state->nintervals].baseoff == state->baseoff);
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tupoff = OffsetNumberNext(PageGetMaxOffsetNumber(newpage));
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if (state->nitems == 1)
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{
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/* Use original, unchanged base tuple */
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tuplesz = IndexTupleSize(state->base);
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if (PageAddItem(newpage, (Item) state->base, tuplesz, tupoff,
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false, false) == InvalidOffsetNumber)
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elog(ERROR, "deduplication failed to add tuple to page");
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spacesaving = 0;
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}
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else
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{
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IndexTuple final;
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|
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/* Form a tuple with a posting list */
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final = _bt_form_posting(state->base, state->htids, state->nhtids);
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tuplesz = IndexTupleSize(final);
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Assert(tuplesz <= state->maxpostingsize);
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/* Save final number of items for posting list */
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state->intervals[state->nintervals].nitems = state->nitems;
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Assert(tuplesz == MAXALIGN(IndexTupleSize(final)));
|
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if (PageAddItem(newpage, (Item) final, tuplesz, tupoff, false,
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false) == InvalidOffsetNumber)
|
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elog(ERROR, "deduplication failed to add tuple to page");
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|
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pfree(final);
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spacesaving = state->phystupsize - (tuplesz + sizeof(ItemIdData));
|
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/* Increment nintervals, since we wrote a new posting list tuple */
|
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state->nintervals++;
|
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Assert(spacesaving > 0 && spacesaving < BLCKSZ);
|
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}
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|
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/* Reset state for next pending posting list */
|
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state->nhtids = 0;
|
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state->nitems = 0;
|
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state->phystupsize = 0;
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|
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return spacesaving;
|
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}
|
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|
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/*
|
|
* Determine if page non-pivot tuples (data items) are all duplicates of the
|
|
* same value -- if they are, deduplication's "single value" strategy should
|
|
* be applied. The general goal of this strategy is to ensure that
|
|
* nbtsplitloc.c (which uses its own single value strategy) will find a useful
|
|
* split point as further duplicates are inserted, and successive rightmost
|
|
* page splits occur among pages that store the same duplicate value. When
|
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* the page finally splits, it should end up BTREE_SINGLEVAL_FILLFACTOR% full,
|
|
* just like it would if deduplication were disabled.
|
|
*
|
|
* We expect that affected workloads will require _several_ single value
|
|
* strategy deduplication passes (over a page that only stores duplicates)
|
|
* before the page is finally split. The first deduplication pass should only
|
|
* find regular non-pivot tuples. Later deduplication passes will find
|
|
* existing maxpostingsize-capped posting list tuples, which must be skipped
|
|
* over. The penultimate pass is generally the first pass that actually
|
|
* reaches _bt_singleval_fillfactor(), and so will deliberately leave behind a
|
|
* few untouched non-pivot tuples. The final deduplication pass won't free
|
|
* any space -- it will skip over everything without merging anything (it
|
|
* retraces the steps of the penultimate pass).
|
|
*
|
|
* Fortunately, having several passes isn't too expensive. Each pass (after
|
|
* the first pass) won't spend many cycles on the large posting list tuples
|
|
* left by previous passes. Each pass will find a large contiguous group of
|
|
* smaller duplicate tuples to merge together at the end of the page.
|
|
*
|
|
* Note: We deliberately don't bother checking if the high key is a distinct
|
|
* value (prior to the TID tiebreaker column) before proceeding, unlike
|
|
* nbtsplitloc.c. Its single value strategy only gets applied on the
|
|
* rightmost page of duplicates of the same value (other leaf pages full of
|
|
* duplicates will get a simple 50:50 page split instead of splitting towards
|
|
* the end of the page). There is little point in making the same distinction
|
|
* here.
|
|
*/
|
|
static bool
|
|
_bt_do_singleval(Relation rel, Page page, BTDedupState state,
|
|
OffsetNumber minoff, IndexTuple newitem)
|
|
{
|
|
int natts = IndexRelationGetNumberOfAttributes(rel);
|
|
ItemId itemid;
|
|
IndexTuple itup;
|
|
|
|
itemid = PageGetItemId(page, minoff);
|
|
itup = (IndexTuple) PageGetItem(page, itemid);
|
|
|
|
if (_bt_keep_natts_fast(rel, newitem, itup) > natts)
|
|
{
|
|
itemid = PageGetItemId(page, PageGetMaxOffsetNumber(page));
|
|
itup = (IndexTuple) PageGetItem(page, itemid);
|
|
|
|
if (_bt_keep_natts_fast(rel, newitem, itup) > natts)
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Lower maxpostingsize when using "single value" strategy, to avoid a sixth
|
|
* and final maxpostingsize-capped tuple. The sixth and final posting list
|
|
* tuple will end up somewhat smaller than the first five. (Note: The first
|
|
* five tuples could actually just be very large duplicate tuples that
|
|
* couldn't be merged together at all. Deduplication will simply not modify
|
|
* the page when that happens.)
|
|
*
|
|
* When there are six posting lists on the page (after current deduplication
|
|
* pass goes on to create/observe a sixth very large tuple), caller should end
|
|
* its deduplication pass. It isn't useful to try to deduplicate items that
|
|
* are supposed to end up on the new right sibling page following the
|
|
* anticipated page split. A future deduplication pass of future right
|
|
* sibling page might take care of it. (This is why the first single value
|
|
* strategy deduplication pass for a given leaf page will generally find only
|
|
* plain non-pivot tuples -- see _bt_do_singleval() comments.)
|
|
*/
|
|
static void
|
|
_bt_singleval_fillfactor(Page page, BTDedupState state, Size newitemsz)
|
|
{
|
|
Size leftfree;
|
|
int reduction;
|
|
|
|
/* This calculation needs to match nbtsplitloc.c */
|
|
leftfree = PageGetPageSize(page) - SizeOfPageHeaderData -
|
|
MAXALIGN(sizeof(BTPageOpaqueData));
|
|
/* Subtract size of new high key (includes pivot heap TID space) */
|
|
leftfree -= newitemsz + MAXALIGN(sizeof(ItemPointerData));
|
|
|
|
/*
|
|
* Reduce maxpostingsize by an amount equal to target free space on left
|
|
* half of page
|
|
*/
|
|
reduction = leftfree * ((100 - BTREE_SINGLEVAL_FILLFACTOR) / 100.0);
|
|
if (state->maxpostingsize > reduction)
|
|
state->maxpostingsize -= reduction;
|
|
else
|
|
state->maxpostingsize = 0;
|
|
}
|
|
|
|
/*
|
|
* Build a posting list tuple based on caller's "base" index tuple and list of
|
|
* heap TIDs. When nhtids == 1, builds a standard non-pivot tuple without a
|
|
* posting list. (Posting list tuples can never have a single heap TID, partly
|
|
* because that ensures that deduplication always reduces final MAXALIGN()'d
|
|
* size of entire tuple.)
|
|
*
|
|
* Convention is that posting list starts at a MAXALIGN()'d offset (rather
|
|
* than a SHORTALIGN()'d offset), in line with the approach taken when
|
|
* appending a heap TID to new pivot tuple/high key during suffix truncation.
|
|
* This sometimes wastes a little space that was only needed as alignment
|
|
* padding in the original tuple. Following this convention simplifies the
|
|
* space accounting used when deduplicating a page (the same convention
|
|
* simplifies the accounting for choosing a point to split a page at).
|
|
*
|
|
* Note: Caller's "htids" array must be unique and already in ascending TID
|
|
* order. Any existing heap TIDs from "base" won't automatically appear in
|
|
* returned posting list tuple (they must be included in htids array.)
|
|
*/
|
|
IndexTuple
|
|
_bt_form_posting(IndexTuple base, ItemPointer htids, int nhtids)
|
|
{
|
|
uint32 keysize,
|
|
newsize;
|
|
IndexTuple itup;
|
|
|
|
if (BTreeTupleIsPosting(base))
|
|
keysize = BTreeTupleGetPostingOffset(base);
|
|
else
|
|
keysize = IndexTupleSize(base);
|
|
|
|
Assert(!BTreeTupleIsPivot(base));
|
|
Assert(nhtids > 0 && nhtids <= PG_UINT16_MAX);
|
|
Assert(keysize == MAXALIGN(keysize));
|
|
|
|
/* Determine final size of new tuple */
|
|
if (nhtids > 1)
|
|
newsize = MAXALIGN(keysize +
|
|
nhtids * sizeof(ItemPointerData));
|
|
else
|
|
newsize = keysize;
|
|
|
|
Assert(newsize <= INDEX_SIZE_MASK);
|
|
Assert(newsize == MAXALIGN(newsize));
|
|
|
|
/* Allocate memory using palloc0() (matches index_form_tuple()) */
|
|
itup = palloc0(newsize);
|
|
memcpy(itup, base, keysize);
|
|
itup->t_info &= ~INDEX_SIZE_MASK;
|
|
itup->t_info |= newsize;
|
|
if (nhtids > 1)
|
|
{
|
|
/* Form posting list tuple */
|
|
BTreeTupleSetPosting(itup, nhtids, keysize);
|
|
memcpy(BTreeTupleGetPosting(itup), htids,
|
|
sizeof(ItemPointerData) * nhtids);
|
|
Assert(_bt_posting_valid(itup));
|
|
}
|
|
else
|
|
{
|
|
/* Form standard non-pivot tuple */
|
|
itup->t_info &= ~INDEX_ALT_TID_MASK;
|
|
ItemPointerCopy(htids, &itup->t_tid);
|
|
Assert(ItemPointerIsValid(&itup->t_tid));
|
|
}
|
|
|
|
return itup;
|
|
}
|
|
|
|
/*
|
|
* Generate a replacement tuple by "updating" a posting list tuple so that it
|
|
* no longer has TIDs that need to be deleted.
|
|
*
|
|
* Used by VACUUM. Caller's vacposting argument points to the existing
|
|
* posting list tuple to be updated.
|
|
*
|
|
* On return, caller's vacposting argument will point to final "updated"
|
|
* tuple, which will be palloc()'d in caller's memory context.
|
|
*/
|
|
void
|
|
_bt_update_posting(BTVacuumPosting vacposting)
|
|
{
|
|
IndexTuple origtuple = vacposting->itup;
|
|
uint32 keysize,
|
|
newsize;
|
|
IndexTuple itup;
|
|
int nhtids;
|
|
int ui,
|
|
d;
|
|
ItemPointer htids;
|
|
|
|
nhtids = BTreeTupleGetNPosting(origtuple) - vacposting->ndeletedtids;
|
|
|
|
Assert(_bt_posting_valid(origtuple));
|
|
Assert(nhtids > 0 && nhtids < BTreeTupleGetNPosting(origtuple));
|
|
|
|
if (BTreeTupleIsPosting(origtuple))
|
|
keysize = BTreeTupleGetPostingOffset(origtuple);
|
|
else
|
|
keysize = IndexTupleSize(origtuple);
|
|
|
|
/*
|
|
* Determine final size of new tuple.
|
|
*
|
|
* This calculation needs to match the code used within _bt_form_posting()
|
|
* for new posting list tuples. We avoid calling _bt_form_posting() here
|
|
* to save ourselves a second memory allocation for a htids workspace.
|
|
*/
|
|
if (nhtids > 1)
|
|
newsize = MAXALIGN(keysize +
|
|
nhtids * sizeof(ItemPointerData));
|
|
else
|
|
newsize = keysize;
|
|
|
|
/* Allocate memory using palloc0() (matches index_form_tuple()) */
|
|
itup = palloc0(newsize);
|
|
memcpy(itup, origtuple, keysize);
|
|
itup->t_info &= ~INDEX_SIZE_MASK;
|
|
itup->t_info |= newsize;
|
|
|
|
if (nhtids > 1)
|
|
{
|
|
/* Form posting list tuple */
|
|
BTreeTupleSetPosting(itup, nhtids, keysize);
|
|
htids = BTreeTupleGetPosting(itup);
|
|
}
|
|
else
|
|
{
|
|
/* Form standard non-pivot tuple */
|
|
itup->t_info &= ~INDEX_ALT_TID_MASK;
|
|
htids = &itup->t_tid;
|
|
}
|
|
|
|
ui = 0;
|
|
d = 0;
|
|
for (int i = 0; i < BTreeTupleGetNPosting(origtuple); i++)
|
|
{
|
|
if (d < vacposting->ndeletedtids && vacposting->deletetids[d] == i)
|
|
{
|
|
d++;
|
|
continue;
|
|
}
|
|
htids[ui++] = *BTreeTupleGetPostingN(origtuple, i);
|
|
}
|
|
Assert(ui == nhtids);
|
|
Assert(d == vacposting->ndeletedtids);
|
|
Assert(nhtids == 1 || _bt_posting_valid(itup));
|
|
|
|
/* vacposting arg's itup will now point to updated version */
|
|
vacposting->itup = itup;
|
|
}
|
|
|
|
/*
|
|
* Prepare for a posting list split by swapping heap TID in newitem with heap
|
|
* TID from original posting list (the 'oposting' heap TID located at offset
|
|
* 'postingoff'). Modifies newitem, so caller should pass their own private
|
|
* copy that can safely be modified.
|
|
*
|
|
* Returns new posting list tuple, which is palloc()'d in caller's context.
|
|
* This is guaranteed to be the same size as 'oposting'. Modified newitem is
|
|
* what caller actually inserts. (This happens inside the same critical
|
|
* section that performs an in-place update of old posting list using new
|
|
* posting list returned here.)
|
|
*
|
|
* While the keys from newitem and oposting must be opclass equal, and must
|
|
* generate identical output when run through the underlying type's output
|
|
* function, it doesn't follow that their representations match exactly.
|
|
* Caller must avoid assuming that there can't be representational differences
|
|
* that make datums from oposting bigger or smaller than the corresponding
|
|
* datums from newitem. For example, differences in TOAST input state might
|
|
* break a faulty assumption about tuple size (the executor is entitled to
|
|
* apply TOAST compression based on its own criteria). It also seems possible
|
|
* that further representational variation will be introduced in the future,
|
|
* in order to support nbtree features like page-level prefix compression.
|
|
*
|
|
* See nbtree/README for details on the design of posting list splits.
|
|
*/
|
|
IndexTuple
|
|
_bt_swap_posting(IndexTuple newitem, IndexTuple oposting, int postingoff)
|
|
{
|
|
int nhtids;
|
|
char *replacepos;
|
|
char *replaceposright;
|
|
Size nmovebytes;
|
|
IndexTuple nposting;
|
|
|
|
nhtids = BTreeTupleGetNPosting(oposting);
|
|
Assert(_bt_posting_valid(oposting));
|
|
Assert(postingoff > 0 && postingoff < nhtids);
|
|
|
|
/*
|
|
* Move item pointers in posting list to make a gap for the new item's
|
|
* heap TID. We shift TIDs one place to the right, losing original
|
|
* rightmost TID. (nmovebytes must not include TIDs to the left of
|
|
* postingoff, nor the existing rightmost/max TID that gets overwritten.)
|
|
*/
|
|
nposting = CopyIndexTuple(oposting);
|
|
replacepos = (char *) BTreeTupleGetPostingN(nposting, postingoff);
|
|
replaceposright = (char *) BTreeTupleGetPostingN(nposting, postingoff + 1);
|
|
nmovebytes = (nhtids - postingoff - 1) * sizeof(ItemPointerData);
|
|
memmove(replaceposright, replacepos, nmovebytes);
|
|
|
|
/* Fill the gap at postingoff with TID of new item (original new TID) */
|
|
Assert(!BTreeTupleIsPivot(newitem) && !BTreeTupleIsPosting(newitem));
|
|
ItemPointerCopy(&newitem->t_tid, (ItemPointer) replacepos);
|
|
|
|
/* Now copy oposting's rightmost/max TID into new item (final new TID) */
|
|
ItemPointerCopy(BTreeTupleGetMaxHeapTID(oposting), &newitem->t_tid);
|
|
|
|
Assert(ItemPointerCompare(BTreeTupleGetMaxHeapTID(nposting),
|
|
BTreeTupleGetHeapTID(newitem)) < 0);
|
|
Assert(_bt_posting_valid(nposting));
|
|
|
|
return nposting;
|
|
}
|
|
|
|
/*
|
|
* Verify posting list invariants for "posting", which must be a posting list
|
|
* tuple. Used within assertions.
|
|
*/
|
|
#ifdef USE_ASSERT_CHECKING
|
|
static bool
|
|
_bt_posting_valid(IndexTuple posting)
|
|
{
|
|
ItemPointerData last;
|
|
ItemPointer htid;
|
|
|
|
if (!BTreeTupleIsPosting(posting) || BTreeTupleGetNPosting(posting) < 2)
|
|
return false;
|
|
|
|
/* Remember first heap TID for loop */
|
|
ItemPointerCopy(BTreeTupleGetHeapTID(posting), &last);
|
|
if (!ItemPointerIsValid(&last))
|
|
return false;
|
|
|
|
/* Iterate, starting from second TID */
|
|
for (int i = 1; i < BTreeTupleGetNPosting(posting); i++)
|
|
{
|
|
htid = BTreeTupleGetPostingN(posting, i);
|
|
|
|
if (!ItemPointerIsValid(htid))
|
|
return false;
|
|
if (ItemPointerCompare(htid, &last) <= 0)
|
|
return false;
|
|
ItemPointerCopy(htid, &last);
|
|
}
|
|
|
|
return true;
|
|
}
|
|
#endif
|