diff options
Diffstat (limited to 'src/backend/access/nbtree/nbtpage.c')
| -rw-r--r-- | src/backend/access/nbtree/nbtpage.c | 149 |
1 files changed, 82 insertions, 67 deletions
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c index 33f85cd59a6..ace06f0a250 100644 --- a/src/backend/access/nbtree/nbtpage.c +++ b/src/backend/access/nbtree/nbtpage.c @@ -9,7 +9,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.66 2003/07/21 20:29:39 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.67 2003/08/04 00:43:15 momjian Exp $ * * NOTES * Postgres btree pages look like ordinary relation pages. The opaque @@ -181,8 +181,8 @@ _bt_getroot(Relation rel, int access) /* * Metadata initialized by someone else. In order to * guarantee no deadlocks, we have to release the metadata - * page and start all over again. (Is that really true? - * But it's hardly worth trying to optimize this case.) + * page and start all over again. (Is that really true? But + * it's hardly worth trying to optimize this case.) */ _bt_relbuf(rel, metabuf); return _bt_getroot(rel, access); @@ -190,8 +190,8 @@ _bt_getroot(Relation rel, int access) /* * Get, initialize, write, and leave a lock of the appropriate - * type on the new root page. Since this is the first page in - * the tree, it's a leaf as well as the root. + * type on the new root page. Since this is the first page in the + * tree, it's a leaf as well as the root. */ rootbuf = _bt_getbuf(rel, P_NEW, BT_WRITE); rootblkno = BufferGetBlockNumber(rootbuf); @@ -240,7 +240,7 @@ _bt_getroot(Relation rel, int access) _bt_wrtnorelbuf(rel, rootbuf); /* - * swap root write lock for read lock. There is no danger of + * swap root write lock for read lock. There is no danger of * anyone else accessing the new root page while it's unlocked, * since no one else knows where it is yet. */ @@ -284,8 +284,8 @@ _bt_getroot(Relation rel, int access) } /* - * By here, we have a pin and read lock on the root page, and no - * lock set on the metadata page. Return the root page's buffer. + * By here, we have a pin and read lock on the root page, and no lock + * set on the metadata page. Return the root page's buffer. */ return rootbuf; } @@ -299,7 +299,7 @@ _bt_getroot(Relation rel, int access) * By the time we acquire lock on the root page, it might have been split and * not be the true root anymore. This is okay for the present uses of this * routine; we only really need to be able to move up at least one tree level - * from whatever non-root page we were at. If we ever do need to lock the + * from whatever non-root page we were at. If we ever do need to lock the * one true root page, we could loop here, re-reading the metapage on each * failure. (Note that it wouldn't do to hold the lock on the metapage while * moving to the root --- that'd deadlock against any concurrent root split.) @@ -406,9 +406,9 @@ _bt_getbuf(Relation rel, BlockNumber blkno, int access) * First see if the FSM knows of any free pages. * * We can't trust the FSM's report unreservedly; we have to check - * that the page is still free. (For example, an already-free page - * could have been re-used between the time the last VACUUM scanned - * it and the time the VACUUM made its FSM updates.) + * that the page is still free. (For example, an already-free + * page could have been re-used between the time the last VACUUM + * scanned it and the time the VACUUM made its FSM updates.) */ for (;;) { @@ -431,10 +431,10 @@ _bt_getbuf(Relation rel, BlockNumber blkno, int access) /* * Extend the relation by one page. * - * We have to use a lock to ensure no one else is extending the rel at - * the same time, else we will both try to initialize the same new - * page. We can skip locking for new or temp relations, however, - * since no one else could be accessing them. + * We have to use a lock to ensure no one else is extending the rel + * at the same time, else we will both try to initialize the same + * new page. We can skip locking for new or temp relations, + * however, since no one else could be accessing them. */ needLock = !(rel->rd_isnew || rel->rd_istemp); @@ -444,8 +444,8 @@ _bt_getbuf(Relation rel, BlockNumber blkno, int access) buf = ReadBuffer(rel, P_NEW); /* - * Release the file-extension lock; it's now OK for someone else to - * extend the relation some more. + * Release the file-extension lock; it's now OK for someone else + * to extend the relation some more. */ if (needLock) UnlockPage(rel, 0, ExclusiveLock); @@ -484,7 +484,7 @@ _bt_relbuf(Relation rel, Buffer buf) * and a pin on the buffer. * * NOTE: actually, the buffer manager just marks the shared buffer page - * dirty here; the real I/O happens later. This is okay since we are not + * dirty here; the real I/O happens later. This is okay since we are not * relying on write ordering anyway. The WAL mechanism is responsible for * guaranteeing correctness after a crash. */ @@ -534,13 +534,14 @@ _bt_page_recyclable(Page page) BTPageOpaque opaque; /* - * It's possible to find an all-zeroes page in an index --- for example, - * a backend might successfully extend the relation one page and then - * crash before it is able to make a WAL entry for adding the page. - * If we find a zeroed page then reclaim it. + * It's possible to find an all-zeroes page in an index --- for + * example, a backend might successfully extend the relation one page + * and then crash before it is able to make a WAL entry for adding the + * page. If we find a zeroed page then reclaim it. */ if (PageIsNew(page)) return true; + /* * Otherwise, recycle if deleted and too old to have any processes * interested in it. @@ -565,7 +566,7 @@ _bt_page_recyclable(Page page) * mistake. On exit, metapage data is correct and we no longer have * a pin or lock on the metapage. * - * Actually this is not used for splitting on-the-fly anymore. It's only used + * Actually this is not used for splitting on-the-fly anymore. It's only used * in nbtsort.c at the completion of btree building, where we know we have * sole access to the index anyway. */ @@ -623,7 +624,7 @@ _bt_metaproot(Relation rel, BlockNumber rootbknum, uint32 level) /* * Delete item(s) from a btree page. * - * This must only be used for deleting leaf items. Deleting an item on a + * This must only be used for deleting leaf items. Deleting an item on a * non-leaf page has to be done as part of an atomic action that includes * deleting the page it points to. * @@ -646,9 +647,7 @@ _bt_delitems(Relation rel, Buffer buf, * adjusting item numbers for previous deletions. */ for (i = nitems - 1; i >= 0; i--) - { PageIndexTupleDelete(page, itemnos[i]); - } /* XLOG stuff */ if (!rel->rd_istemp) @@ -666,8 +665,8 @@ _bt_delitems(Relation rel, Buffer buf, rdata[0].next = &(rdata[1]); /* - * The target-offsets array is not in the buffer, but pretend - * that it is. When XLogInsert stores the whole buffer, the offsets + * The target-offsets array is not in the buffer, but pretend that + * it is. When XLogInsert stores the whole buffer, the offsets * array need not be stored too. */ rdata[1].buffer = buf; @@ -701,7 +700,7 @@ _bt_delitems(Relation rel, Buffer buf, * may currently be trying to follow links leading to the page; they have to * be allowed to use its right-link to recover. See nbtree/README. * - * On entry, the target buffer must be pinned and read-locked. This lock and + * On entry, the target buffer must be pinned and read-locked. This lock and * pin will be dropped before exiting. * * Returns the number of pages successfully deleted (zero on failure; could @@ -714,7 +713,7 @@ _bt_delitems(Relation rel, Buffer buf, int _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) { - BlockNumber target, + BlockNumber target, leftsib, rightsib, parent; @@ -740,17 +739,18 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) BTPageOpaque opaque; /* - * We can never delete rightmost pages nor root pages. While at it, + * We can never delete rightmost pages nor root pages. While at it, * check that page is not already deleted and is empty. */ page = BufferGetPage(buf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque) || - P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page)) + P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page)) { _bt_relbuf(rel, buf); return 0; } + /* * Save info about page, including a copy of its high key (it must * have one, being non-rightmost). @@ -760,12 +760,13 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) leftsib = opaque->btpo_prev; itemid = PageGetItemId(page, P_HIKEY); targetkey = CopyBTItem((BTItem) PageGetItem(page, itemid)); + /* * We need to get an approximate pointer to the page's parent page. - * Use the standard search mechanism to search for the page's high key; - * this will give us a link to either the current parent or someplace - * to its left (if there are multiple equal high keys). To avoid - * deadlocks, we'd better drop the target page lock first. + * Use the standard search mechanism to search for the page's high + * key; this will give us a link to either the current parent or + * someplace to its left (if there are multiple equal high keys). To + * avoid deadlocks, we'd better drop the target page lock first. */ _bt_relbuf(rel, buf); /* we need a scan key to do our search, so build one */ @@ -775,9 +776,11 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) &lbuf, BT_READ); /* don't need a pin on that either */ _bt_relbuf(rel, lbuf); + /* * If we are trying to delete an interior page, _bt_search did more - * than we needed. Locate the stack item pointing to our parent level. + * than we needed. Locate the stack item pointing to our parent + * level. */ ilevel = 0; for (;;) @@ -789,10 +792,12 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) stack = stack->bts_parent; ilevel++; } + /* * We have to lock the pages we need to modify in the standard order: - * moving right, then up. Else we will deadlock against other writers. - * + * moving right, then up. Else we will deadlock against other + * writers. + * * So, we need to find and write-lock the current left sibling of the * target page. The sibling that was current a moment ago could have * split, so we may have to move right. This search could fail if @@ -823,21 +828,24 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) } else lbuf = InvalidBuffer; + /* - * Next write-lock the target page itself. It should be okay to take just - * a write lock not a superexclusive lock, since no scans would stop on an - * empty page. + * Next write-lock the target page itself. It should be okay to take + * just a write lock not a superexclusive lock, since no scans would + * stop on an empty page. */ buf = _bt_getbuf(rel, target, BT_WRITE); page = BufferGetPage(buf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); + /* - * Check page is still empty etc, else abandon deletion. The empty check - * is necessary since someone else might have inserted into it while - * we didn't have it locked; the others are just for paranoia's sake. + * Check page is still empty etc, else abandon deletion. The empty + * check is necessary since someone else might have inserted into it + * while we didn't have it locked; the others are just for paranoia's + * sake. */ if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque) || - P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page)) + P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page)) { _bt_relbuf(rel, buf); if (BufferIsValid(lbuf)) @@ -846,14 +854,17 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) } if (opaque->btpo_prev != leftsib) elog(ERROR, "left link changed unexpectedly"); + /* * And next write-lock the (current) right sibling. */ rightsib = opaque->btpo_next; rbuf = _bt_getbuf(rel, rightsib, BT_WRITE); + /* * Next find and write-lock the current parent of the target page. - * This is essentially the same as the corresponding step of splitting. + * This is essentially the same as the corresponding step of + * splitting. */ ItemPointerSet(&(stack->bts_btitem.bti_itup.t_tid), target, P_HIKEY); @@ -863,10 +874,11 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) RelationGetRelationName(rel)); parent = stack->bts_blkno; poffset = stack->bts_offset; + /* * If the target is the rightmost child of its parent, then we can't - * delete, unless it's also the only child --- in which case the parent - * changes to half-dead status. + * delete, unless it's also the only child --- in which case the + * parent changes to half-dead status. */ page = BufferGetPage(pbuf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); @@ -893,12 +905,13 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) if (OffsetNumberNext(P_FIRSTDATAKEY(opaque)) == maxoff) parent_one_child = true; } + /* * If we are deleting the next-to-last page on the target's level, - * then the rightsib is a candidate to become the new fast root. - * (In theory, it might be possible to push the fast root even further - * down, but the odds of doing so are slim, and the locking considerations - * daunting.) + * then the rightsib is a candidate to become the new fast root. (In + * theory, it might be possible to push the fast root even further + * down, but the odds of doing so are slim, and the locking + * considerations daunting.) * * We can safely acquire a lock on the metapage here --- see comments for * _bt_newroot(). @@ -914,12 +927,13 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE); metapg = BufferGetPage(metabuf); metad = BTPageGetMeta(metapg); + /* * The expected case here is btm_fastlevel == targetlevel+1; - * if the fastlevel is <= targetlevel, something is wrong, and we - * choose to overwrite it to fix it. + * if the fastlevel is <= targetlevel, something is wrong, and + * we choose to overwrite it to fix it. */ - if (metad->btm_fastlevel > targetlevel+1) + if (metad->btm_fastlevel > targetlevel + 1) { /* no update wanted */ _bt_relbuf(rel, metabuf); @@ -937,9 +951,9 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) /* * Update parent. The normal case is a tad tricky because we want to - * delete the target's downlink and the *following* key. Easiest way is - * to copy the right sibling's downlink over the target downlink, and then - * delete the following item. + * delete the target's downlink and the *following* key. Easiest way + * is to copy the right sibling's downlink over the target downlink, + * and then delete the following item. */ page = BufferGetPage(pbuf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); @@ -950,7 +964,7 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) } else { - OffsetNumber nextoffset; + OffsetNumber nextoffset; itemid = PageGetItemId(page, poffset); btitem = (BTItem) PageGetItem(page, itemid); @@ -968,8 +982,8 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) } /* - * Update siblings' side-links. Note the target page's side-links will - * continue to point to the siblings. + * Update siblings' side-links. Note the target page's side-links + * will continue to point to the siblings. */ if (BufferIsValid(lbuf)) { @@ -1096,10 +1110,11 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full) _bt_wrtbuf(rel, lbuf); /* - * If parent became half dead, recurse to try to delete it. Otherwise, - * if right sibling is empty and is now the last child of the parent, - * recurse to try to delete it. (These cases cannot apply at the same - * time, though the second case might itself recurse to the first.) + * If parent became half dead, recurse to try to delete it. + * Otherwise, if right sibling is empty and is now the last child of + * the parent, recurse to try to delete it. (These cases cannot apply + * at the same time, though the second case might itself recurse to + * the first.) */ if (parent_half_dead) { |