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postgresql/src/include/access/visibilitymap.h

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Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
/*-------------------------------------------------------------------------
*
* visibilitymap.h
8.4 pgindent run, with new combined Linux/FreeBSD/MinGW typedef list provided by Andrew.
2009-06-11 16:49:15 +02:00
* visibility map interface
Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
*
*
Update copyright for 2019 Backpatch-through: certain files through 9.4
2019-01-02 18:44:25 +01:00
* Portions Copyright (c) 2007-2019, PostgreSQL Global Development Group
Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
* Portions Copyright (c) 1994, Regents of the University of California
*
Remove cvs keywords from all files.
2010-09-20 22:08:53 +02:00
* src/include/access/visibilitymap.h
Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
*
*-------------------------------------------------------------------------
*/
#ifndef VISIBILITYMAP_H
#define VISIBILITYMAP_H
#include "access/xlogdefs.h"
Fix a violation of WAL coding rules in the recent patch to include an "all tuples visible" flag in heap page headers. The flag update *must* be applied before calling XLogInsert, but heap_update and the tuple moving routines in VACUUM FULL were ignoring this rule. A crash and replay could therefore leave the flag incorrectly set, causing rows to appear visible in seqscans when they should not be. This might explain recent reports of data corruption from Jeff Ross and others. In passing, do a bit of editorialization on comments in visibilitymap.c.
2009-08-24 04:18:32 +02:00
#include "storage/block.h"
#include "storage/buf.h"
#include "utils/relcache.h"
Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
Cosmetic improvements to freeze map code. Per post-commit review comments from Andres Freund, improve variable names, comments, and in one place, slightly improve the code structure. Masahiko Sawada
2016-06-03 14:43:41 +02:00
/* Number of bits for one heap page */
Change the format of the VM fork to add a second bit per page. The new bit indicates whether every tuple on the page is already frozen. It is cleared only when the all-visible bit is cleared, and it can be set only when we vacuum a page and find that every tuple on that page is both visible to every transaction and in no need of any future vacuuming. A future commit will use this new bit to optimize away full-table scans that would otherwise be triggered by XID wraparound considerations. A page which is merely all-visible must still be scanned in that case, but a page which is all-frozen need not be. This commit does not attempt that optimization, although that optimization is the goal here. It seems better to get the basic infrastructure in place first. Per discussion, it's very desirable for pg_upgrade to automatically migrate existing VM forks from the old format to the new format. That, too, will be handled in a follow-on patch. Masahiko Sawada, reviewed by Kyotaro Horiguchi, Fujii Masao, Amit Kapila, Simon Riggs, Andres Freund, and others, and substantially revised by me.
2016-03-02 03:49:41 +01:00
#define BITS_PER_HEAPBLOCK 2
/* Flags for bit map */
#define VISIBILITYMAP_ALL_VISIBLE 0x01
#define VISIBILITYMAP_ALL_FROZEN 0x02
Phase 2 of pgindent updates. Change pg_bsd_indent to follow upstream rules for placement of comments to the right of code, and remove pgindent hack that caused comments following #endif to not obey the general rule. Commit e3860ffa4dd0dad0dd9eea4be9cc1412373a8c89 wasn't actually using the published version of pg_bsd_indent, but a hacked-up version that tried to minimize the amount of movement of comments to the right of code. The situation of interest is where such a comment has to be moved to the right of its default placement at column 33 because there's code there. BSD indent has always moved right in units of tab stops in such cases --- but in the previous incarnation, indent was working in 8-space tab stops, while now it knows we use 4-space tabs. So the net result is that in about half the cases, such comments are placed one tab stop left of before. This is better all around: it leaves more room on the line for comment text, and it means that in such cases the comment uniformly starts at the next 4-space tab stop after the code, rather than sometimes one and sometimes two tabs after. Also, ensure that comments following #endif are indented the same as comments following other preprocessor commands such as #else. That inconsistency turns out to have been self-inflicted damage from a poorly-thought-through post-indent "fixup" in pgindent. This patch is much less interesting than the first round of indent changes, but also bulkier, so I thought it best to separate the effects. Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
2017-06-21 21:18:54 +02:00
#define VISIBILITYMAP_VALID_BITS 0x03 /* OR of all valid visibilitymap
* flags bits */
Change the format of the VM fork to add a second bit per page. The new bit indicates whether every tuple on the page is already frozen. It is cleared only when the all-visible bit is cleared, and it can be set only when we vacuum a page and find that every tuple on that page is both visible to every transaction and in no need of any future vacuuming. A future commit will use this new bit to optimize away full-table scans that would otherwise be triggered by XID wraparound considerations. A page which is merely all-visible must still be scanned in that case, but a page which is all-frozen need not be. This commit does not attempt that optimization, although that optimization is the goal here. It seems better to get the basic infrastructure in place first. Per discussion, it's very desirable for pg_upgrade to automatically migrate existing VM forks from the old format to the new format. That, too, will be handled in a follow-on patch. Masahiko Sawada, reviewed by Kyotaro Horiguchi, Fujii Masao, Amit Kapila, Simon Riggs, Andres Freund, and others, and substantially revised by me.
2016-03-02 03:49:41 +01:00
/* Macros for visibilitymap test */
#define VM_ALL_VISIBLE(r, b, v) \
((visibilitymap_get_status((r), (b), (v)) & VISIBILITYMAP_ALL_VISIBLE) != 0)
#define VM_ALL_FROZEN(r, b, v) \
((visibilitymap_get_status((r), (b), (v)) & VISIBILITYMAP_ALL_FROZEN) != 0)
Clear all-frozen visibilitymap status when locking tuples. Since a892234 & fd31cd265 the visibilitymap's freeze bit is used to avoid vacuuming the whole relation in anti-wraparound vacuums. Doing so correctly relies on not adding xids to the heap without also unsetting the visibilitymap flag. Tuple locking related code has not done so. To allow selectively resetting all-frozen - to avoid pessimizing heap_lock_tuple - allow to selectively reset the all-frozen with visibilitymap_clear(). To avoid having to use visibilitymap_get_status (e.g. via VM_ALL_FROZEN) inside a critical section, have visibilitymap_clear() return whether any bits have been reset. There's a remaining issue (denoted by XXX): After the PageIsAllVisible() check in heap_lock_tuple() and heap_lock_updated_tuple_rec() the page status could theoretically change. Practically that currently seems impossible, because updaters will hold a page level pin already. Due to the next beta coming up, it seems better to get the required WAL magic bump done before resolving this issue. The added flags field fields to xl_heap_lock and xl_heap_lock_updated require bumping the WAL magic. Since there's already been a catversion bump since the last beta, that's not an issue. Reviewed-By: Robert Haas, Amit Kapila and Andres Freund Author: Masahiko Sawada, heavily revised by Andres Freund Discussion: CAEepm=3fWAbWryVW9swHyLTY4sXVf0xbLvXqOwUoDiNCx9mBjQ@mail.gmail.com Backpatch: -
2016-07-18 11:01:13 +02:00
extern bool visibilitymap_clear(Relation rel, BlockNumber heapBlk,
Buffer vmbuf, uint8 flags);
Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
extern void visibilitymap_pin(Relation rel, BlockNumber heapBlk,
8.4 pgindent run, with new combined Linux/FreeBSD/MinGW typedef list provided by Andrew.
2009-06-11 16:49:15 +02:00
Buffer *vmbuf);
Make the visibility map crash-safe. This involves two main changes from the previous behavior. First, when we set a bit in the visibility map, emit a new WAL record of type XLOG_HEAP2_VISIBLE. Replay sets the page-level PD_ALL_VISIBLE bit and the visibility map bit. Second, when inserting, updating, or deleting a tuple, we can no longer get away with clearing the visibility map bit after releasing the lock on the corresponding heap page, because an intervening crash might leave the visibility map bit set and the page-level bit clear. Making this work requires a bit of interface refactoring. In passing, a few minor but related cleanups: change the test in visibilitymap_set and visibilitymap_clear to throw an error if the wrong page (or no page) is pinned, rather than silently doing nothing; this case should never occur. Also, remove duplicate definitions of InvalidXLogRecPtr. Patch by me, review by Noah Misch.
2011-06-22 05:04:40 +02:00
extern bool visibilitymap_pin_ok(BlockNumber heapBlk, Buffer vmbuf);
Allow I/O reliability checks using 16-bit checksums Checksums are set immediately prior to flush out of shared buffers and checked when pages are read in again. Hint bit setting will require full page write when block is dirtied, which causes various infrastructure changes. Extensive comments, docs and README. WARNING message thrown if checksum fails on non-all zeroes page; ERROR thrown but can be disabled with ignore_checksum_failure = on. Feature enabled by an initdb option, since transition from option off to option on is long and complex and has not yet been implemented. Default is not to use checksums. Checksum used is WAL CRC-32 truncated to 16-bits. Simon Riggs, Jeff Davis, Greg Smith Wide input and assistance from many community members. Thank you.
2013-03-22 14:54:07 +01:00
extern void visibilitymap_set(Relation rel, BlockNumber heapBlk, Buffer heapBuf,
pgindent run for 9.6
2016-06-10 00:02:36 +02:00
XLogRecPtr recptr, Buffer vmBuf, TransactionId cutoff_xid,
uint8 flags);
Change the format of the VM fork to add a second bit per page. The new bit indicates whether every tuple on the page is already frozen. It is cleared only when the all-visible bit is cleared, and it can be set only when we vacuum a page and find that every tuple on that page is both visible to every transaction and in no need of any future vacuuming. A future commit will use this new bit to optimize away full-table scans that would otherwise be triggered by XID wraparound considerations. A page which is merely all-visible must still be scanned in that case, but a page which is all-frozen need not be. This commit does not attempt that optimization, although that optimization is the goal here. It seems better to get the basic infrastructure in place first. Per discussion, it's very desirable for pg_upgrade to automatically migrate existing VM forks from the old format to the new format. That, too, will be handled in a follow-on patch. Masahiko Sawada, reviewed by Kyotaro Horiguchi, Fujii Masao, Amit Kapila, Simon Riggs, Andres Freund, and others, and substantially revised by me.
2016-03-02 03:49:41 +01:00
extern uint8 visibilitymap_get_status(Relation rel, BlockNumber heapBlk, Buffer *vmbuf);
extern void visibilitymap_count(Relation rel, BlockNumber *all_visible, BlockNumber *all_frozen);
Measure the number of all-visible pages for use in index-only scan costing. Add a column pg_class.relallvisible to remember the number of pages that were all-visible according to the visibility map as of the last VACUUM (or ANALYZE, or some other operations that update pg_class.relpages). Use relallvisible/relpages, instead of an arbitrary constant, to estimate how many heap page fetches can be avoided during an index-only scan. This is pretty primitive and will no doubt see refinements once we've acquired more field experience with the index-only scan mechanism, but it's way better than using a constant. Note: I had to adjust an underspecified query in the window.sql regression test, because it was changing answers when the plan changed to use an index-only scan. Some of the adjacent tests perhaps should be adjusted as well, but I didn't do that here.
2011-10-14 23:23:01 +02:00
extern void visibilitymap_truncate(Relation rel, BlockNumber nheapblocks);
Introduce visibility map. The visibility map is a bitmap with one bit per heap page, where a set bit indicates that all tuples on the page are visible to all transactions, and the page therefore doesn't need vacuuming. It is stored in a new relation fork. Lazy vacuum uses the visibility map to skip pages that don't need vacuuming. Vacuum is also responsible for setting the bits in the map. In the future, this can hopefully be used to implement index-only-scans, but we can't currently guarantee that the visibility map is always 100% up-to-date. In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on each heap page, also indicating that all tuples on the page are visible to all transactions. It's important that this flag is kept up-to-date. It is also used to skip visibility tests in sequential scans, which gives a small performance gain on seqscans.
2008-12-03 14:05:22 +01:00
Phase 2 of pgindent updates. Change pg_bsd_indent to follow upstream rules for placement of comments to the right of code, and remove pgindent hack that caused comments following #endif to not obey the general rule. Commit e3860ffa4dd0dad0dd9eea4be9cc1412373a8c89 wasn't actually using the published version of pg_bsd_indent, but a hacked-up version that tried to minimize the amount of movement of comments to the right of code. The situation of interest is where such a comment has to be moved to the right of its default placement at column 33 because there's code there. BSD indent has always moved right in units of tab stops in such cases --- but in the previous incarnation, indent was working in 8-space tab stops, while now it knows we use 4-space tabs. So the net result is that in about half the cases, such comments are placed one tab stop left of before. This is better all around: it leaves more room on the line for comment text, and it means that in such cases the comment uniformly starts at the next 4-space tab stop after the code, rather than sometimes one and sometimes two tabs after. Also, ensure that comments following #endif are indented the same as comments following other preprocessor commands such as #else. That inconsistency turns out to have been self-inflicted damage from a poorly-thought-through post-indent "fixup" in pgindent. This patch is much less interesting than the first round of indent changes, but also bulkier, so I thought it best to separate the effects. Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
2017-06-21 21:18:54 +02:00
#endif /* VISIBILITYMAP_H */