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f741300c90
Instead of truncating pg_multixact at vacuum time, do it only at checkpoint time. The reason for doing it this way is twofold: first, we want it to delete only segments that we're certain will not be required if there's a crash immediately after the removal; and second, we want to do it relatively often so that older files are not left behind if there's an untimely crash. Per my proposal in http://www.postgresql.org/message-id/20140626044519.GJ7340@eldon.alvh.no-ip.org we now execute the truncation in the checkpointer process rather than as part of vacuum. Vacuum is in only charge of maintaining in shared memory the value to which it's possible to truncate the files; that value is stored as part of checkpoints also, and so upon recovery we can reuse the same value to re-execute truncate and reset the oldest-value-still-safe-to-use to one known to remain after truncation. Per bug reported by Jeff Janes in the course of his tests involving bug #8673. While at it, update some comments that hadn't been updated since multixacts were changed. Backpatch to 9.3, where persistency of pg_multixact files was introduced by commit 0ac5ad5134f2.
143 lines
4.6 KiB
C
143 lines
4.6 KiB
C
/*
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* multixact.h
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*
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* PostgreSQL multi-transaction-log manager
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*
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* Portions Copyright (c) 1996-2014, 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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* src/include/access/multixact.h
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*/
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#ifndef MULTIXACT_H
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#define MULTIXACT_H
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#include "access/xlog.h"
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/*
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* The first two MultiXactId values are reserved to store the truncation Xid
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* and epoch of the first segment, so we start assigning multixact values from
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* 2.
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*/
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#define InvalidMultiXactId ((MultiXactId) 0)
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#define FirstMultiXactId ((MultiXactId) 1)
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#define MaxMultiXactId ((MultiXactId) 0xFFFFFFFF)
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#define MultiXactIdIsValid(multi) ((multi) != InvalidMultiXactId)
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#define MaxMultiXactOffset ((MultiXactOffset) 0xFFFFFFFF)
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/* Number of SLRU buffers to use for multixact */
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#define NUM_MXACTOFFSET_BUFFERS 8
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#define NUM_MXACTMEMBER_BUFFERS 16
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/*
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* Possible multixact lock modes ("status"). The first four modes are for
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* tuple locks (FOR KEY SHARE, FOR SHARE, FOR NO KEY UPDATE, FOR UPDATE); the
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* next two are used for update and delete modes.
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*/
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typedef enum
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{
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MultiXactStatusForKeyShare = 0x00,
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MultiXactStatusForShare = 0x01,
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MultiXactStatusForNoKeyUpdate = 0x02,
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MultiXactStatusForUpdate = 0x03,
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/* an update that doesn't touch "key" columns */
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MultiXactStatusNoKeyUpdate = 0x04,
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/* other updates, and delete */
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MultiXactStatusUpdate = 0x05
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} MultiXactStatus;
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#define MaxMultiXactStatus MultiXactStatusUpdate
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/* does a status value correspond to a tuple update? */
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#define ISUPDATE_from_mxstatus(status) \
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((status) > MultiXactStatusForUpdate)
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typedef struct MultiXactMember
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{
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TransactionId xid;
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MultiXactStatus status;
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} MultiXactMember;
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/* ----------------
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* multixact-related XLOG entries
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* ----------------
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*/
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#define XLOG_MULTIXACT_ZERO_OFF_PAGE 0x00
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#define XLOG_MULTIXACT_ZERO_MEM_PAGE 0x10
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#define XLOG_MULTIXACT_CREATE_ID 0x20
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typedef struct xl_multixact_create
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{
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MultiXactId mid; /* new MultiXact's ID */
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MultiXactOffset moff; /* its starting offset in members file */
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int32 nmembers; /* number of member XIDs */
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MultiXactMember members[FLEXIBLE_ARRAY_MEMBER];
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} xl_multixact_create;
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#define SizeOfMultiXactCreate (offsetof(xl_multixact_create, members))
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extern MultiXactId MultiXactIdCreate(TransactionId xid1,
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MultiXactStatus status1, TransactionId xid2,
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MultiXactStatus status2);
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extern MultiXactId MultiXactIdExpand(MultiXactId multi, TransactionId xid,
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MultiXactStatus status);
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extern MultiXactId MultiXactIdCreateFromMembers(int nmembers,
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MultiXactMember *members);
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extern MultiXactId ReadNextMultiXactId(void);
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extern bool MultiXactIdIsRunning(MultiXactId multi);
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extern void MultiXactIdSetOldestMember(void);
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extern int GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **xids,
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bool allow_old);
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extern bool MultiXactHasRunningRemoteMembers(MultiXactId multi);
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extern bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2);
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extern bool MultiXactIdPrecedesOrEquals(MultiXactId multi1,
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MultiXactId multi2);
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extern void AtEOXact_MultiXact(void);
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extern void AtPrepare_MultiXact(void);
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extern void PostPrepare_MultiXact(TransactionId xid);
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extern Size MultiXactShmemSize(void);
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extern void MultiXactShmemInit(void);
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extern void BootStrapMultiXact(void);
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extern void StartupMultiXact(void);
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extern void TrimMultiXact(void);
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extern void ShutdownMultiXact(void);
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extern void SetMultiXactIdLimit(MultiXactId oldest_datminmxid,
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Oid oldest_datoid);
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extern void MultiXactGetCheckptMulti(bool is_shutdown,
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MultiXactId *nextMulti,
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MultiXactOffset *nextMultiOffset,
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MultiXactId *oldestMulti,
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Oid *oldestMultiDB);
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extern void CheckPointMultiXact(void);
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extern MultiXactId GetOldestMultiXactId(void);
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extern void TruncateMultiXact(void);
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extern void MultiXactSetNextMXact(MultiXactId nextMulti,
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MultiXactOffset nextMultiOffset);
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extern void MultiXactAdvanceNextMXact(MultiXactId minMulti,
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MultiXactOffset minMultiOffset);
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extern void MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB);
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extern void MultiXactSetSafeTruncate(MultiXactId safeTruncateMulti);
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extern void multixact_twophase_recover(TransactionId xid, uint16 info,
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void *recdata, uint32 len);
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extern void multixact_twophase_postcommit(TransactionId xid, uint16 info,
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void *recdata, uint32 len);
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extern void multixact_twophase_postabort(TransactionId xid, uint16 info,
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void *recdata, uint32 len);
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extern void multixact_redo(XLogRecPtr lsn, XLogRecord *record);
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extern void multixact_desc(StringInfo buf, XLogRecord *record);
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extern char *mxid_to_string(MultiXactId multi, int nmembers,
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MultiXactMember *members);
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#endif /* MULTIXACT_H */
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