/*------------------------------------------------------------------------- * * md.c * This code manages relations that reside on magnetic disk. * * Or at least, that was what the Berkeley folk had in mind when they named * this file. In reality, what this code provides is an interface from * the smgr API to Unix-like filesystem APIs, so it will work with any type * of device for which the operating system provides filesystem support. * It doesn't matter whether the bits are on spinning rust or some other * storage technology. * * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/storage/smgr/md.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include #include #include #include "miscadmin.h" #include "access/xlog.h" #include "catalog/catalog.h" #include "portability/instr_time.h" #include "postmaster/bgwriter.h" #include "storage/fd.h" #include "storage/bufmgr.h" #include "storage/relfilenode.h" #include "storage/smgr.h" #include "utils/hsearch.h" #include "utils/memutils.h" #include "pg_trace.h" /* intervals for calling AbsorbFsyncRequests in mdsync and mdpostckpt */ #define FSYNCS_PER_ABSORB 10 #define UNLINKS_PER_ABSORB 10 /* * Special values for the segno arg to RememberFsyncRequest. * * Note that CompactCheckpointerRequestQueue assumes that it's OK to remove an * fsync request from the queue if an identical, subsequent request is found. * See comments there before making changes here. */ #define FORGET_RELATION_FSYNC (InvalidBlockNumber) #define FORGET_DATABASE_FSYNC (InvalidBlockNumber-1) #define UNLINK_RELATION_REQUEST (InvalidBlockNumber-2) /* * On Windows, we have to interpret EACCES as possibly meaning the same as * ENOENT, because if a file is unlinked-but-not-yet-gone on that platform, * that's what you get. Ugh. This code is designed so that we don't * actually believe these cases are okay without further evidence (namely, * a pending fsync request getting canceled ... see mdsync). */ #ifndef WIN32 #define FILE_POSSIBLY_DELETED(err) ((err) == ENOENT) #else #define FILE_POSSIBLY_DELETED(err) ((err) == ENOENT || (err) == EACCES) #endif /* * The magnetic disk storage manager keeps track of open file * descriptors in its own descriptor pool. This is done to make it * easier to support relations that are larger than the operating * system's file size limit (often 2GBytes). In order to do that, * we break relations up into "segment" files that are each shorter than * the OS file size limit. The segment size is set by the RELSEG_SIZE * configuration constant in pg_config.h. * * On disk, a relation must consist of consecutively numbered segment * files in the pattern * -- Zero or more full segments of exactly RELSEG_SIZE blocks each * -- Exactly one partial segment of size 0 <= size < RELSEG_SIZE blocks * -- Optionally, any number of inactive segments of size 0 blocks. * The full and partial segments are collectively the "active" segments. * Inactive segments are those that once contained data but are currently * not needed because of an mdtruncate() operation. The reason for leaving * them present at size zero, rather than unlinking them, is that other * backends and/or the checkpointer might be holding open file references to * such segments. If the relation expands again after mdtruncate(), such * that a deactivated segment becomes active again, it is important that * such file references still be valid --- else data might get written * out to an unlinked old copy of a segment file that will eventually * disappear. * * The file descriptor pointer (md_fd field) stored in the SMgrRelation * cache is, therefore, just the head of a list of MdfdVec objects, one * per segment. But note the md_fd pointer can be NULL, indicating * relation not open. * * Also note that mdfd_chain == NULL does not necessarily mean the relation * doesn't have another segment after this one; we may just not have * opened the next segment yet. (We could not have "all segments are * in the chain" as an invariant anyway, since another backend could * extend the relation when we weren't looking.) We do not make chain * entries for inactive segments, however; as soon as we find a partial * segment, we assume that any subsequent segments are inactive. * * All MdfdVec objects are palloc'd in the MdCxt memory context. */ typedef struct _MdfdVec { File mdfd_vfd; /* fd number in fd.c's pool */ BlockNumber mdfd_segno; /* segment number, from 0 */ struct _MdfdVec *mdfd_chain; /* next segment, or NULL */ } MdfdVec; static MemoryContext MdCxt; /* context for all md.c allocations */ /* * In some contexts (currently, standalone backends and the checkpointer) * we keep track of pending fsync operations: we need to remember all relation * segments that have been written since the last checkpoint, so that we can * fsync them down to disk before completing the next checkpoint. This hash * table remembers the pending operations. We use a hash table mostly as * a convenient way of merging duplicate requests. * * We use a similar mechanism to remember no-longer-needed files that can * be deleted after the next checkpoint, but we use a linked list instead of * a hash table, because we don't expect there to be any duplicate requests. * * These mechanisms are only used for non-temp relations; we never fsync * temp rels, nor do we need to postpone their deletion (see comments in * mdunlink). * * (Regular backends do not track pending operations locally, but forward * them to the checkpointer.) */ typedef uint16 CycleCtr; /* can be any convenient integer size */ typedef struct { RelFileNode rnode; /* hash table key (must be first!) */ CycleCtr cycle_ctr; /* mdsync_cycle_ctr of oldest request */ /* requests[f] has bit n set if we need to fsync segment n of fork f */ Bitmapset *requests[MAX_FORKNUM + 1]; /* canceled[f] is true if we canceled fsyncs for fork "recently" */ bool canceled[MAX_FORKNUM + 1]; } PendingOperationEntry; typedef struct { RelFileNode rnode; /* the dead relation to delete */ CycleCtr cycle_ctr; /* mdckpt_cycle_ctr when request was made */ } PendingUnlinkEntry; static HTAB *pendingOpsTable = NULL; static List *pendingUnlinks = NIL; static CycleCtr mdsync_cycle_ctr = 0; static CycleCtr mdckpt_cycle_ctr = 0; typedef enum /* behavior for mdopen & _mdfd_getseg */ { EXTENSION_FAIL, /* ereport if segment not present */ EXTENSION_RETURN_NULL, /* return NULL if not present */ EXTENSION_CREATE /* create new segments as needed */ } ExtensionBehavior; /* local routines */ static void mdunlinkfork(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo); static MdfdVec *mdopen(SMgrRelation reln, ForkNumber forknum, ExtensionBehavior behavior); static void register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg); static void register_unlink(RelFileNodeBackend rnode); static MdfdVec *_fdvec_alloc(void); static char *_mdfd_segpath(SMgrRelation reln, ForkNumber forknum, BlockNumber segno); static MdfdVec *_mdfd_openseg(SMgrRelation reln, ForkNumber forkno, BlockNumber segno, int oflags); static MdfdVec *_mdfd_getseg(SMgrRelation reln, ForkNumber forkno, BlockNumber blkno, bool skipFsync, ExtensionBehavior behavior); static BlockNumber _mdnblocks(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg); /* * mdinit() -- Initialize private state for magnetic disk storage manager. */ void mdinit(void) { MdCxt = AllocSetContextCreate(TopMemoryContext, "MdSmgr", ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE); /* * Create pending-operations hashtable if we need it. Currently, we need * it if we are standalone (not under a postmaster) or if we are a startup * or checkpointer auxiliary process. */ if (!IsUnderPostmaster || AmStartupProcess() || AmCheckpointerProcess()) { HASHCTL hash_ctl; MemSet(&hash_ctl, 0, sizeof(hash_ctl)); hash_ctl.keysize = sizeof(RelFileNode); hash_ctl.entrysize = sizeof(PendingOperationEntry); hash_ctl.hash = tag_hash; hash_ctl.hcxt = MdCxt; pendingOpsTable = hash_create("Pending Ops Table", 100L, &hash_ctl, HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT); pendingUnlinks = NIL; } } /* * In archive recovery, we rely on checkpointer to do fsyncs, but we will have * already created the pendingOpsTable during initialization of the startup * process. Calling this function drops the local pendingOpsTable so that * subsequent requests will be forwarded to checkpointer. */ void SetForwardFsyncRequests(void) { /* Perform any pending fsyncs we may have queued up, then drop table */ if (pendingOpsTable) { mdsync(); hash_destroy(pendingOpsTable); } pendingOpsTable = NULL; /* * We should not have any pending unlink requests, since mdunlink doesn't * queue unlink requests when isRedo. */ Assert(pendingUnlinks == NIL); } /* * mdexists() -- Does the physical file exist? * * Note: this will return true for lingering files, with pending deletions */ bool mdexists(SMgrRelation reln, ForkNumber forkNum) { /* * Close it first, to ensure that we notice if the fork has been unlinked * since we opened it. */ mdclose(reln, forkNum); return (mdopen(reln, forkNum, EXTENSION_RETURN_NULL) != NULL); } /* * mdcreate() -- Create a new relation on magnetic disk. * * If isRedo is true, it's okay for the relation to exist already. */ void mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo) { char *path; File fd; if (isRedo && reln->md_fd[forkNum] != NULL) return; /* created and opened already... */ Assert(reln->md_fd[forkNum] == NULL); path = relpath(reln->smgr_rnode, forkNum); fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY, 0600); if (fd < 0) { int save_errno = errno; /* * During bootstrap, there are cases where a system relation will be * accessed (by internal backend processes) before the bootstrap * script nominally creates it. Therefore, allow the file to exist * already, even if isRedo is not set. (See also mdopen) */ if (isRedo || IsBootstrapProcessingMode()) fd = PathNameOpenFile(path, O_RDWR | PG_BINARY, 0600); if (fd < 0) { /* be sure to report the error reported by create, not open */ errno = save_errno; ereport(ERROR, (errcode_for_file_access(), errmsg("could not create file \"%s\": %m", path))); } } pfree(path); reln->md_fd[forkNum] = _fdvec_alloc(); reln->md_fd[forkNum]->mdfd_vfd = fd; reln->md_fd[forkNum]->mdfd_segno = 0; reln->md_fd[forkNum]->mdfd_chain = NULL; } /* * mdunlink() -- Unlink a relation. * * Note that we're passed a RelFileNodeBackend --- by the time this is called, * there won't be an SMgrRelation hashtable entry anymore. * * forkNum can be a fork number to delete a specific fork, or InvalidForkNumber * to delete all forks. * * For regular relations, we don't unlink the first segment file of the rel, * but just truncate it to zero length, and record a request to unlink it after * the next checkpoint. Additional segments can be unlinked immediately, * however. Leaving the empty file in place prevents that relfilenode * number from being reused. The scenario this protects us from is: * 1. We delete a relation (and commit, and actually remove its file). * 2. We create a new relation, which by chance gets the same relfilenode as * the just-deleted one (OIDs must've wrapped around for that to happen). * 3. We crash before another checkpoint occurs. * During replay, we would delete the file and then recreate it, which is fine * if the contents of the file were repopulated by subsequent WAL entries. * But if we didn't WAL-log insertions, but instead relied on fsyncing the * file after populating it (as for instance CLUSTER and CREATE INDEX do), * the contents of the file would be lost forever. By leaving the empty file * until after the next checkpoint, we prevent reassignment of the relfilenode * number until it's safe, because relfilenode assignment skips over any * existing file. * * We do not need to go through this dance for temp relations, though, because * we never make WAL entries for temp rels, and so a temp rel poses no threat * to the health of a regular rel that has taken over its relfilenode number. * The fact that temp rels and regular rels have different file naming * patterns provides additional safety. * * All the above applies only to the relation's main fork; other forks can * just be removed immediately, since they are not needed to prevent the * relfilenode number from being recycled. Also, we do not carefully * track whether other forks have been created or not, but just attempt to * unlink them unconditionally; so we should never complain about ENOENT. * * If isRedo is true, it's unsurprising for the relation to be already gone. * Also, we should remove the file immediately instead of queuing a request * for later, since during redo there's no possibility of creating a * conflicting relation. * * Note: any failure should be reported as WARNING not ERROR, because * we are usually not in a transaction anymore when this is called. */ void mdunlink(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo) { /* * We have to clean out any pending fsync requests for the doomed * relation, else the next mdsync() will fail. There can't be any such * requests for a temp relation, though. We can send just one request * even when deleting multiple forks, since the fsync queuing code accepts * the "InvalidForkNumber = all forks" convention. */ if (!RelFileNodeBackendIsTemp(rnode)) ForgetRelationFsyncRequests(rnode.node, forkNum); /* Now do the per-fork work */ if (forkNum == InvalidForkNumber) { for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++) mdunlinkfork(rnode, forkNum, isRedo); } else mdunlinkfork(rnode, forkNum, isRedo); } static void mdunlinkfork(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo) { char *path; int ret; path = relpath(rnode, forkNum); /* * Delete or truncate the first segment. */ if (isRedo || forkNum != MAIN_FORKNUM || RelFileNodeBackendIsTemp(rnode)) { ret = unlink(path); if (ret < 0 && errno != ENOENT) ereport(WARNING, (errcode_for_file_access(), errmsg("could not remove file \"%s\": %m", path))); } else { /* truncate(2) would be easier here, but Windows hasn't got it */ int fd; fd = OpenTransientFile(path, O_RDWR | PG_BINARY, 0); if (fd >= 0) { int save_errno; ret = ftruncate(fd, 0); save_errno = errno; CloseTransientFile(fd); errno = save_errno; } else ret = -1; if (ret < 0 && errno != ENOENT) ereport(WARNING, (errcode_for_file_access(), errmsg("could not truncate file \"%s\": %m", path))); /* Register request to unlink first segment later */ register_unlink(rnode); } /* * Delete any additional segments. */ if (ret >= 0) { char *segpath = (char *) palloc(strlen(path) + 12); BlockNumber segno; /* * Note that because we loop until getting ENOENT, we will correctly * remove all inactive segments as well as active ones. */ for (segno = 1;; segno++) { sprintf(segpath, "%s.%u", path, segno); if (unlink(segpath) < 0) { /* ENOENT is expected after the last segment... */ if (errno != ENOENT) ereport(WARNING, (errcode_for_file_access(), errmsg("could not remove file \"%s\": %m", segpath))); break; } } pfree(segpath); } pfree(path); } /* * mdextend() -- Add a block to the specified relation. * * The semantics are nearly the same as mdwrite(): write at the * specified position. However, this is to be used for the case of * extending a relation (i.e., blocknum is at or beyond the current * EOF). Note that we assume writing a block beyond current EOF * causes intervening file space to become filled with zeroes. */ void mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer, bool skipFsync) { off_t seekpos; int nbytes; MdfdVec *v; /* This assert is too expensive to have on normally ... */ #ifdef CHECK_WRITE_VS_EXTEND Assert(blocknum >= mdnblocks(reln, forknum)); #endif /* * If a relation manages to grow to 2^32-1 blocks, refuse to extend it any * more --- we mustn't create a block whose number actually is * InvalidBlockNumber. */ if (blocknum == InvalidBlockNumber) ereport(ERROR, (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), errmsg("cannot extend file \"%s\" beyond %u blocks", relpath(reln->smgr_rnode, forknum), InvalidBlockNumber))); v = _mdfd_getseg(reln, forknum, blocknum, skipFsync, EXTENSION_CREATE); seekpos = (off_t) BLCKSZ *(blocknum % ((BlockNumber) RELSEG_SIZE)); Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE); /* * Note: because caller usually obtained blocknum by calling mdnblocks, * which did a seek(SEEK_END), this seek is often redundant and will be * optimized away by fd.c. It's not redundant, however, if there is a * partial page at the end of the file. In that case we want to try to * overwrite the partial page with a full page. It's also not redundant * if bufmgr.c had to dump another buffer of the same file to make room * for the new page's buffer. */ if (FileSeek(v->mdfd_vfd, seekpos, SEEK_SET) != seekpos) ereport(ERROR, (errcode_for_file_access(), errmsg("could not seek to block %u in file \"%s\": %m", blocknum, FilePathName(v->mdfd_vfd)))); if ((nbytes = FileWrite(v->mdfd_vfd, buffer, BLCKSZ)) != BLCKSZ) { if (nbytes < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not extend file \"%s\": %m", FilePathName(v->mdfd_vfd)), errhint("Check free disk space."))); /* short write: complain appropriately */ ereport(ERROR, (errcode(ERRCODE_DISK_FULL), errmsg("could not extend file \"%s\": wrote only %d of %d bytes at block %u", FilePathName(v->mdfd_vfd), nbytes, BLCKSZ, blocknum), errhint("Check free disk space."))); } if (!skipFsync && !SmgrIsTemp(reln)) register_dirty_segment(reln, forknum, v); Assert(_mdnblocks(reln, forknum, v) <= ((BlockNumber) RELSEG_SIZE)); } /* * mdopen() -- Open the specified relation. * * Note we only open the first segment, when there are multiple segments. * * If first segment is not present, either ereport or return NULL according * to "behavior". We treat EXTENSION_CREATE the same as EXTENSION_FAIL; * EXTENSION_CREATE means it's OK to extend an existing relation, not to * invent one out of whole cloth. */ static MdfdVec * mdopen(SMgrRelation reln, ForkNumber forknum, ExtensionBehavior behavior) { MdfdVec *mdfd; char *path; File fd; /* No work if already open */ if (reln->md_fd[forknum]) return reln->md_fd[forknum]; path = relpath(reln->smgr_rnode, forknum); fd = PathNameOpenFile(path, O_RDWR | PG_BINARY, 0600); if (fd < 0) { /* * During bootstrap, there are cases where a system relation will be * accessed (by internal backend processes) before the bootstrap * script nominally creates it. Therefore, accept mdopen() as a * substitute for mdcreate() in bootstrap mode only. (See mdcreate) */ if (IsBootstrapProcessingMode()) fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY, 0600); if (fd < 0) { if (behavior == EXTENSION_RETURN_NULL && FILE_POSSIBLY_DELETED(errno)) { pfree(path); return NULL; } ereport(ERROR, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", path))); } } pfree(path); reln->md_fd[forknum] = mdfd = _fdvec_alloc(); mdfd->mdfd_vfd = fd; mdfd->mdfd_segno = 0; mdfd->mdfd_chain = NULL; Assert(_mdnblocks(reln, forknum, mdfd) <= ((BlockNumber) RELSEG_SIZE)); return mdfd; } /* * mdclose() -- Close the specified relation, if it isn't closed already. */ void mdclose(SMgrRelation reln, ForkNumber forknum) { MdfdVec *v = reln->md_fd[forknum]; /* No work if already closed */ if (v == NULL) return; reln->md_fd[forknum] = NULL; /* prevent dangling pointer after error */ while (v != NULL) { MdfdVec *ov = v; /* if not closed already */ if (v->mdfd_vfd >= 0) FileClose(v->mdfd_vfd); /* Now free vector */ v = v->mdfd_chain; pfree(ov); } } /* * mdprefetch() -- Initiate asynchronous read of the specified block of a relation */ void mdprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum) { #ifdef USE_PREFETCH off_t seekpos; MdfdVec *v; v = _mdfd_getseg(reln, forknum, blocknum, false, EXTENSION_FAIL); seekpos = (off_t) BLCKSZ *(blocknum % ((BlockNumber) RELSEG_SIZE)); Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE); (void) FilePrefetch(v->mdfd_vfd, seekpos, BLCKSZ); #endif /* USE_PREFETCH */ } /* * mdread() -- Read the specified block from a relation. */ void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer) { off_t seekpos; int nbytes; MdfdVec *v; TRACE_POSTGRESQL_SMGR_MD_READ_START(forknum, blocknum, reln->smgr_rnode.node.spcNode, reln->smgr_rnode.node.dbNode, reln->smgr_rnode.node.relNode, reln->smgr_rnode.backend); v = _mdfd_getseg(reln, forknum, blocknum, false, EXTENSION_FAIL); seekpos = (off_t) BLCKSZ *(blocknum % ((BlockNumber) RELSEG_SIZE)); Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE); if (FileSeek(v->mdfd_vfd, seekpos, SEEK_SET) != seekpos) ereport(ERROR, (errcode_for_file_access(), errmsg("could not seek to block %u in file \"%s\": %m", blocknum, FilePathName(v->mdfd_vfd)))); nbytes = FileRead(v->mdfd_vfd, buffer, BLCKSZ); TRACE_POSTGRESQL_SMGR_MD_READ_DONE(forknum, blocknum, reln->smgr_rnode.node.spcNode, reln->smgr_rnode.node.dbNode, reln->smgr_rnode.node.relNode, reln->smgr_rnode.backend, nbytes, BLCKSZ); if (nbytes != BLCKSZ) { if (nbytes < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not read block %u in file \"%s\": %m", blocknum, FilePathName(v->mdfd_vfd)))); /* * Short read: we are at or past EOF, or we read a partial block at * EOF. Normally this is an error; upper levels should never try to * read a nonexistent block. However, if zero_damaged_pages is ON or * we are InRecovery, we should instead return zeroes without * complaining. This allows, for example, the case of trying to * update a block that was later truncated away. */ if (zero_damaged_pages || InRecovery) MemSet(buffer, 0, BLCKSZ); else ereport(ERROR, (errcode(ERRCODE_DATA_CORRUPTED), errmsg("could not read block %u in file \"%s\": read only %d of %d bytes", blocknum, FilePathName(v->mdfd_vfd), nbytes, BLCKSZ))); } } /* * mdwrite() -- Write the supplied block at the appropriate location. * * This is to be used only for updating already-existing blocks of a * relation (ie, those before the current EOF). To extend a relation, * use mdextend(). */ void mdwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer, bool skipFsync) { off_t seekpos; int nbytes; MdfdVec *v; /* This assert is too expensive to have on normally ... */ #ifdef CHECK_WRITE_VS_EXTEND Assert(blocknum < mdnblocks(reln, forknum)); #endif TRACE_POSTGRESQL_SMGR_MD_WRITE_START(forknum, blocknum, reln->smgr_rnode.node.spcNode, reln->smgr_rnode.node.dbNode, reln->smgr_rnode.node.relNode, reln->smgr_rnode.backend); v = _mdfd_getseg(reln, forknum, blocknum, skipFsync, EXTENSION_FAIL); seekpos = (off_t) BLCKSZ *(blocknum % ((BlockNumber) RELSEG_SIZE)); Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE); if (FileSeek(v->mdfd_vfd, seekpos, SEEK_SET) != seekpos) ereport(ERROR, (errcode_for_file_access(), errmsg("could not seek to block %u in file \"%s\": %m", blocknum, FilePathName(v->mdfd_vfd)))); nbytes = FileWrite(v->mdfd_vfd, buffer, BLCKSZ); TRACE_POSTGRESQL_SMGR_MD_WRITE_DONE(forknum, blocknum, reln->smgr_rnode.node.spcNode, reln->smgr_rnode.node.dbNode, reln->smgr_rnode.node.relNode, reln->smgr_rnode.backend, nbytes, BLCKSZ); if (nbytes != BLCKSZ) { if (nbytes < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not write block %u in file \"%s\": %m", blocknum, FilePathName(v->mdfd_vfd)))); /* short write: complain appropriately */ ereport(ERROR, (errcode(ERRCODE_DISK_FULL), errmsg("could not write block %u in file \"%s\": wrote only %d of %d bytes", blocknum, FilePathName(v->mdfd_vfd), nbytes, BLCKSZ), errhint("Check free disk space."))); } if (!skipFsync && !SmgrIsTemp(reln)) register_dirty_segment(reln, forknum, v); } /* * mdnblocks() -- Get the number of blocks stored in a relation. * * Important side effect: all active segments of the relation are opened * and added to the mdfd_chain list. If this routine has not been * called, then only segments up to the last one actually touched * are present in the chain. */ BlockNumber mdnblocks(SMgrRelation reln, ForkNumber forknum) { MdfdVec *v = mdopen(reln, forknum, EXTENSION_FAIL); BlockNumber nblocks; BlockNumber segno = 0; /* * Skip through any segments that aren't the last one, to avoid redundant * seeks on them. We have previously verified that these segments are * exactly RELSEG_SIZE long, and it's useless to recheck that each time. * * NOTE: this assumption could only be wrong if another backend has * truncated the relation. We rely on higher code levels to handle that * scenario by closing and re-opening the md fd, which is handled via * relcache flush. (Since the checkpointer doesn't participate in * relcache flush, it could have segment chain entries for inactive * segments; that's OK because the checkpointer never needs to compute * relation size.) */ while (v->mdfd_chain != NULL) { segno++; v = v->mdfd_chain; } for (;;) { nblocks = _mdnblocks(reln, forknum, v); if (nblocks > ((BlockNumber) RELSEG_SIZE)) elog(FATAL, "segment too big"); if (nblocks < ((BlockNumber) RELSEG_SIZE)) return (segno * ((BlockNumber) RELSEG_SIZE)) + nblocks; /* * If segment is exactly RELSEG_SIZE, advance to next one. */ segno++; if (v->mdfd_chain == NULL) { /* * Because we pass O_CREAT, we will create the next segment (with * zero length) immediately, if the last segment is of length * RELSEG_SIZE. While perhaps not strictly necessary, this keeps * the logic simple. */ v->mdfd_chain = _mdfd_openseg(reln, forknum, segno, O_CREAT); if (v->mdfd_chain == NULL) ereport(ERROR, (errcode_for_file_access(), errmsg("could not open file \"%s\": %m", _mdfd_segpath(reln, forknum, segno)))); } v = v->mdfd_chain; } } /* * mdtruncate() -- Truncate relation to specified number of blocks. */ void mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks) { MdfdVec *v; BlockNumber curnblk; BlockNumber priorblocks; /* * NOTE: mdnblocks makes sure we have opened all active segments, so that * truncation loop will get them all! */ curnblk = mdnblocks(reln, forknum); if (nblocks > curnblk) { /* Bogus request ... but no complaint if InRecovery */ if (InRecovery) return; ereport(ERROR, (errmsg("could not truncate file \"%s\" to %u blocks: it's only %u blocks now", relpath(reln->smgr_rnode, forknum), nblocks, curnblk))); } if (nblocks == curnblk) return; /* no work */ v = mdopen(reln, forknum, EXTENSION_FAIL); priorblocks = 0; while (v != NULL) { MdfdVec *ov = v; if (priorblocks > nblocks) { /* * This segment is no longer active (and has already been unlinked * from the mdfd_chain). We truncate the file, but do not delete * it, for reasons explained in the header comments. */ if (FileTruncate(v->mdfd_vfd, 0) < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not truncate file \"%s\": %m", FilePathName(v->mdfd_vfd)))); if (!SmgrIsTemp(reln)) register_dirty_segment(reln, forknum, v); v = v->mdfd_chain; Assert(ov != reln->md_fd[forknum]); /* we never drop the 1st * segment */ pfree(ov); } else if (priorblocks + ((BlockNumber) RELSEG_SIZE) > nblocks) { /* * This is the last segment we want to keep. Truncate the file to * the right length, and clear chain link that points to any * remaining segments (which we shall zap). NOTE: if nblocks is * exactly a multiple K of RELSEG_SIZE, we will truncate the K+1st * segment to 0 length but keep it. This adheres to the invariant * given in the header comments. */ BlockNumber lastsegblocks = nblocks - priorblocks; if (FileTruncate(v->mdfd_vfd, (off_t) lastsegblocks * BLCKSZ) < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not truncate file \"%s\" to %u blocks: %m", FilePathName(v->mdfd_vfd), nblocks))); if (!SmgrIsTemp(reln)) register_dirty_segment(reln, forknum, v); v = v->mdfd_chain; ov->mdfd_chain = NULL; } else { /* * We still need this segment and 0 or more blocks beyond it, so * nothing to do here. */ v = v->mdfd_chain; } priorblocks += RELSEG_SIZE; } } /* * mdimmedsync() -- Immediately sync a relation to stable storage. * * Note that only writes already issued are synced; this routine knows * nothing of dirty buffers that may exist inside the buffer manager. */ void mdimmedsync(SMgrRelation reln, ForkNumber forknum) { MdfdVec *v; /* * NOTE: mdnblocks makes sure we have opened all active segments, so that * fsync loop will get them all! */ mdnblocks(reln, forknum); v = mdopen(reln, forknum, EXTENSION_FAIL); while (v != NULL) { if (FileSync(v->mdfd_vfd) < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not fsync file \"%s\": %m", FilePathName(v->mdfd_vfd)))); v = v->mdfd_chain; } } /* * mdsync() -- Sync previous writes to stable storage. */ void mdsync(void) { static bool mdsync_in_progress = false; HASH_SEQ_STATUS hstat; PendingOperationEntry *entry; int absorb_counter; /* Statistics on sync times */ int processed = 0; instr_time sync_start, sync_end, sync_diff; uint64 elapsed; uint64 longest = 0; uint64 total_elapsed = 0; /* * This is only called during checkpoints, and checkpoints should only * occur in processes that have created a pendingOpsTable. */ if (!pendingOpsTable) elog(ERROR, "cannot sync without a pendingOpsTable"); /* * If we are in the checkpointer, the sync had better include all fsync * requests that were queued by backends up to this point. The tightest * race condition that could occur is that a buffer that must be written * and fsync'd for the checkpoint could have been dumped by a backend just * before it was visited by BufferSync(). We know the backend will have * queued an fsync request before clearing the buffer's dirtybit, so we * are safe as long as we do an Absorb after completing BufferSync(). */ AbsorbFsyncRequests(); /* * To avoid excess fsync'ing (in the worst case, maybe a never-terminating * checkpoint), we want to ignore fsync requests that are entered into the * hashtable after this point --- they should be processed next time, * instead. We use mdsync_cycle_ctr to tell old entries apart from new * ones: new ones will have cycle_ctr equal to the incremented value of * mdsync_cycle_ctr. * * In normal circumstances, all entries present in the table at this point * will have cycle_ctr exactly equal to the current (about to be old) * value of mdsync_cycle_ctr. However, if we fail partway through the * fsync'ing loop, then older values of cycle_ctr might remain when we * come back here to try again. Repeated checkpoint failures would * eventually wrap the counter around to the point where an old entry * might appear new, causing us to skip it, possibly allowing a checkpoint * to succeed that should not have. To forestall wraparound, any time the * previous mdsync() failed to complete, run through the table and * forcibly set cycle_ctr = mdsync_cycle_ctr. * * Think not to merge this loop with the main loop, as the problem is * exactly that that loop may fail before having visited all the entries. * From a performance point of view it doesn't matter anyway, as this path * will never be taken in a system that's functioning normally. */ if (mdsync_in_progress) { /* prior try failed, so update any stale cycle_ctr values */ hash_seq_init(&hstat, pendingOpsTable); while ((entry = (PendingOperationEntry *) hash_seq_search(&hstat)) != NULL) { entry->cycle_ctr = mdsync_cycle_ctr; } } /* Advance counter so that new hashtable entries are distinguishable */ mdsync_cycle_ctr++; /* Set flag to detect failure if we don't reach the end of the loop */ mdsync_in_progress = true; /* Now scan the hashtable for fsync requests to process */ absorb_counter = FSYNCS_PER_ABSORB; hash_seq_init(&hstat, pendingOpsTable); while ((entry = (PendingOperationEntry *) hash_seq_search(&hstat)) != NULL) { ForkNumber forknum; /* * If the entry is new then don't process it this time; it might * contain multiple fsync-request bits, but they are all new. Note * "continue" bypasses the hash-remove call at the bottom of the loop. */ if (entry->cycle_ctr == mdsync_cycle_ctr) continue; /* Else assert we haven't missed it */ Assert((CycleCtr) (entry->cycle_ctr + 1) == mdsync_cycle_ctr); /* * Scan over the forks and segments represented by the entry. * * The bitmap manipulations are slightly tricky, because we can call * AbsorbFsyncRequests() inside the loop and that could result in * bms_add_member() modifying and even re-palloc'ing the bitmapsets. * This is okay because we unlink each bitmapset from the hashtable * entry before scanning it. That means that any incoming fsync * requests will be processed now if they reach the table before we * begin to scan their fork. */ for (forknum = 0; forknum <= MAX_FORKNUM; forknum++) { Bitmapset *requests = entry->requests[forknum]; int segno; entry->requests[forknum] = NULL; entry->canceled[forknum] = false; while ((segno = bms_first_member(requests)) >= 0) { int failures; /* * If fsync is off then we don't have to bother opening the * file at all. (We delay checking until this point so that * changing fsync on the fly behaves sensibly.) */ if (!enableFsync) continue; /* * If in checkpointer, we want to absorb pending requests * every so often to prevent overflow of the fsync request * queue. It is unspecified whether newly-added entries will * be visited by hash_seq_search, but we don't care since we * don't need to process them anyway. */ if (--absorb_counter <= 0) { AbsorbFsyncRequests(); absorb_counter = FSYNCS_PER_ABSORB; } /* * The fsync table could contain requests to fsync segments * that have been deleted (unlinked) by the time we get to * them. Rather than just hoping an ENOENT (or EACCES on * Windows) error can be ignored, what we do on error is * absorb pending requests and then retry. Since mdunlink() * queues a "cancel" message before actually unlinking, the * fsync request is guaranteed to be marked canceled after the * absorb if it really was this case. DROP DATABASE likewise * has to tell us to forget fsync requests before it starts * deletions. */ for (failures = 0;; failures++) /* loop exits at "break" */ { SMgrRelation reln; MdfdVec *seg; char *path; int save_errno; /* * Find or create an smgr hash entry for this relation. * This may seem a bit unclean -- md calling smgr? But * it's really the best solution. It ensures that the * open file reference isn't permanently leaked if we get * an error here. (You may say "but an unreferenced * SMgrRelation is still a leak!" Not really, because the * only case in which a checkpoint is done by a process * that isn't about to shut down is in the checkpointer, * and it will periodically do smgrcloseall(). This fact * justifies our not closing the reln in the success path * either, which is a good thing since in non-checkpointer * cases we couldn't safely do that.) */ reln = smgropen(entry->rnode, InvalidBackendId); /* Attempt to open and fsync the target segment */ seg = _mdfd_getseg(reln, forknum, (BlockNumber) segno * (BlockNumber) RELSEG_SIZE, false, EXTENSION_RETURN_NULL); INSTR_TIME_SET_CURRENT(sync_start); if (seg != NULL && FileSync(seg->mdfd_vfd) >= 0) { /* Success; update statistics about sync timing */ INSTR_TIME_SET_CURRENT(sync_end); sync_diff = sync_end; INSTR_TIME_SUBTRACT(sync_diff, sync_start); elapsed = INSTR_TIME_GET_MICROSEC(sync_diff); if (elapsed > longest) longest = elapsed; total_elapsed += elapsed; processed++; if (log_checkpoints) elog(DEBUG1, "checkpoint sync: number=%d file=%s time=%.3f msec", processed, FilePathName(seg->mdfd_vfd), (double) elapsed / 1000); break; /* out of retry loop */ } /* Compute file name for use in message */ save_errno = errno; path = _mdfd_segpath(reln, forknum, (BlockNumber) segno); errno = save_errno; /* * It is possible that the relation has been dropped or * truncated since the fsync request was entered. * Therefore, allow ENOENT, but only if we didn't fail * already on this file. This applies both for * _mdfd_getseg() and for FileSync, since fd.c might have * closed the file behind our back. * * XXX is there any point in allowing more than one retry? * Don't see one at the moment, but easy to change the * test here if so. */ if (!FILE_POSSIBLY_DELETED(errno) || failures > 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not fsync file \"%s\": %m", path))); else ereport(DEBUG1, (errcode_for_file_access(), errmsg("could not fsync file \"%s\" but retrying: %m", path))); pfree(path); /* * Absorb incoming requests and check to see if a cancel * arrived for this relation fork. */ AbsorbFsyncRequests(); absorb_counter = FSYNCS_PER_ABSORB; /* might as well... */ if (entry->canceled[forknum]) break; } /* end retry loop */ } bms_free(requests); } /* * We've finished everything that was requested before we started to * scan the entry. If no new requests have been inserted meanwhile, * remove the entry. Otherwise, update its cycle counter, as all the * requests now in it must have arrived during this cycle. */ for (forknum = 0; forknum <= MAX_FORKNUM; forknum++) { if (entry->requests[forknum] != NULL) break; } if (forknum <= MAX_FORKNUM) entry->cycle_ctr = mdsync_cycle_ctr; else { /* Okay to remove it */ if (hash_search(pendingOpsTable, &entry->rnode, HASH_REMOVE, NULL) == NULL) elog(ERROR, "pendingOpsTable corrupted"); } } /* end loop over hashtable entries */ /* Return sync performance metrics for report at checkpoint end */ CheckpointStats.ckpt_sync_rels = processed; CheckpointStats.ckpt_longest_sync = longest; CheckpointStats.ckpt_agg_sync_time = total_elapsed; /* Flag successful completion of mdsync */ mdsync_in_progress = false; } /* * mdpreckpt() -- Do pre-checkpoint work * * To distinguish unlink requests that arrived before this checkpoint * started from those that arrived during the checkpoint, we use a cycle * counter similar to the one we use for fsync requests. That cycle * counter is incremented here. * * This must be called *before* the checkpoint REDO point is determined. * That ensures that we won't delete files too soon. * * Note that we can't do anything here that depends on the assumption * that the checkpoint will be completed. */ void mdpreckpt(void) { /* * Any unlink requests arriving after this point will be assigned the next * cycle counter, and won't be unlinked until next checkpoint. */ mdckpt_cycle_ctr++; } /* * mdpostckpt() -- Do post-checkpoint work * * Remove any lingering files that can now be safely removed. */ void mdpostckpt(void) { int absorb_counter; absorb_counter = UNLINKS_PER_ABSORB; while (pendingUnlinks != NIL) { PendingUnlinkEntry *entry = (PendingUnlinkEntry *) linitial(pendingUnlinks); char *path; /* * New entries are appended to the end, so if the entry is new we've * reached the end of old entries. * * Note: if just the right number of consecutive checkpoints fail, we * could be fooled here by cycle_ctr wraparound. However, the only * consequence is that we'd delay unlinking for one more checkpoint, * which is perfectly tolerable. */ if (entry->cycle_ctr == mdckpt_cycle_ctr) break; /* Unlink the file */ path = relpathperm(entry->rnode, MAIN_FORKNUM); if (unlink(path) < 0) { /* * There's a race condition, when the database is dropped at the * same time that we process the pending unlink requests. If the * DROP DATABASE deletes the file before we do, we will get ENOENT * here. rmtree() also has to ignore ENOENT errors, to deal with * the possibility that we delete the file first. */ if (errno != ENOENT) ereport(WARNING, (errcode_for_file_access(), errmsg("could not remove file \"%s\": %m", path))); } pfree(path); /* And remove the list entry */ pendingUnlinks = list_delete_first(pendingUnlinks); pfree(entry); /* * As in mdsync, we don't want to stop absorbing fsync requests for a * long time when there are many deletions to be done. We can safely * call AbsorbFsyncRequests() at this point in the loop (note it might * try to delete list entries). */ if (--absorb_counter <= 0) { AbsorbFsyncRequests(); absorb_counter = UNLINKS_PER_ABSORB; } } } /* * register_dirty_segment() -- Mark a relation segment as needing fsync * * If there is a local pending-ops table, just make an entry in it for * mdsync to process later. Otherwise, try to pass off the fsync request * to the checkpointer process. If that fails, just do the fsync * locally before returning (we hope this will not happen often enough * to be a performance problem). */ static void register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg) { /* Temp relations should never be fsync'd */ Assert(!SmgrIsTemp(reln)); if (pendingOpsTable) { /* push it into local pending-ops table */ RememberFsyncRequest(reln->smgr_rnode.node, forknum, seg->mdfd_segno); } else { if (ForwardFsyncRequest(reln->smgr_rnode.node, forknum, seg->mdfd_segno)) return; /* passed it off successfully */ ereport(DEBUG1, (errmsg("could not forward fsync request because request queue is full"))); if (FileSync(seg->mdfd_vfd) < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not fsync file \"%s\": %m", FilePathName(seg->mdfd_vfd)))); } } /* * register_unlink() -- Schedule a file to be deleted after next checkpoint * * We don't bother passing in the fork number, because this is only used * with main forks. * * As with register_dirty_segment, this could involve either a local or * a remote pending-ops table. */ static void register_unlink(RelFileNodeBackend rnode) { /* Should never be used with temp relations */ Assert(!RelFileNodeBackendIsTemp(rnode)); if (pendingOpsTable) { /* push it into local pending-ops table */ RememberFsyncRequest(rnode.node, MAIN_FORKNUM, UNLINK_RELATION_REQUEST); } else { /* * Notify the checkpointer about it. If we fail to queue the request * message, we have to sleep and try again, because we can't simply * delete the file now. Ugly, but hopefully won't happen often. * * XXX should we just leave the file orphaned instead? */ Assert(IsUnderPostmaster); while (!ForwardFsyncRequest(rnode.node, MAIN_FORKNUM, UNLINK_RELATION_REQUEST)) pg_usleep(10000L); /* 10 msec seems a good number */ } } /* * RememberFsyncRequest() -- callback from checkpointer side of fsync request * * We stuff fsync requests into the local hash table for execution * during the checkpointer's next checkpoint. UNLINK requests go into a * separate linked list, however, because they get processed separately. * * The range of possible segment numbers is way less than the range of * BlockNumber, so we can reserve high values of segno for special purposes. * We define three: * - FORGET_RELATION_FSYNC means to cancel pending fsyncs for a relation, * either for one fork, or all forks if forknum is InvalidForkNumber * - FORGET_DATABASE_FSYNC means to cancel pending fsyncs for a whole database * - UNLINK_RELATION_REQUEST is a request to delete the file after the next * checkpoint. * Note also that we're assuming real segment numbers don't exceed INT_MAX. * * (Handling FORGET_DATABASE_FSYNC requests is a tad slow because the hash * table has to be searched linearly, but dropping a database is a pretty * heavyweight operation anyhow, so we'll live with it.) */ void RememberFsyncRequest(RelFileNode rnode, ForkNumber forknum, BlockNumber segno) { Assert(pendingOpsTable); if (segno == FORGET_RELATION_FSYNC) { /* Remove any pending requests for the relation (one or all forks) */ PendingOperationEntry *entry; entry = (PendingOperationEntry *) hash_search(pendingOpsTable, &rnode, HASH_FIND, NULL); if (entry) { /* * We can't just delete the entry since mdsync could have an * active hashtable scan. Instead we delete the bitmapsets; this * is safe because of the way mdsync is coded. We also set the * "canceled" flags so that mdsync can tell that a cancel arrived * for the fork(s). */ if (forknum == InvalidForkNumber) { /* remove requests for all forks */ for (forknum = 0; forknum <= MAX_FORKNUM; forknum++) { bms_free(entry->requests[forknum]); entry->requests[forknum] = NULL; entry->canceled[forknum] = true; } } else { /* remove requests for single fork */ bms_free(entry->requests[forknum]); entry->requests[forknum] = NULL; entry->canceled[forknum] = true; } } } else if (segno == FORGET_DATABASE_FSYNC) { /* Remove any pending requests for the entire database */ HASH_SEQ_STATUS hstat; PendingOperationEntry *entry; ListCell *cell, *prev, *next; /* Remove fsync requests */ hash_seq_init(&hstat, pendingOpsTable); while ((entry = (PendingOperationEntry *) hash_seq_search(&hstat)) != NULL) { if (entry->rnode.dbNode == rnode.dbNode) { /* remove requests for all forks */ for (forknum = 0; forknum <= MAX_FORKNUM; forknum++) { bms_free(entry->requests[forknum]); entry->requests[forknum] = NULL; entry->canceled[forknum] = true; } } } /* Remove unlink requests */ prev = NULL; for (cell = list_head(pendingUnlinks); cell; cell = next) { PendingUnlinkEntry *entry = (PendingUnlinkEntry *) lfirst(cell); next = lnext(cell); if (entry->rnode.dbNode == rnode.dbNode) { pendingUnlinks = list_delete_cell(pendingUnlinks, cell, prev); pfree(entry); } else prev = cell; } } else if (segno == UNLINK_RELATION_REQUEST) { /* Unlink request: put it in the linked list */ MemoryContext oldcxt = MemoryContextSwitchTo(MdCxt); PendingUnlinkEntry *entry; /* PendingUnlinkEntry doesn't store forknum, since it's always MAIN */ Assert(forknum == MAIN_FORKNUM); entry = palloc(sizeof(PendingUnlinkEntry)); entry->rnode = rnode; entry->cycle_ctr = mdckpt_cycle_ctr; pendingUnlinks = lappend(pendingUnlinks, entry); MemoryContextSwitchTo(oldcxt); } else { /* Normal case: enter a request to fsync this segment */ MemoryContext oldcxt = MemoryContextSwitchTo(MdCxt); PendingOperationEntry *entry; bool found; entry = (PendingOperationEntry *) hash_search(pendingOpsTable, &rnode, HASH_ENTER, &found); /* if new entry, initialize it */ if (!found) { entry->cycle_ctr = mdsync_cycle_ctr; MemSet(entry->requests, 0, sizeof(entry->requests)); MemSet(entry->canceled, 0, sizeof(entry->canceled)); } /* * NB: it's intentional that we don't change cycle_ctr if the entry * already exists. The cycle_ctr must represent the oldest fsync * request that could be in the entry. */ entry->requests[forknum] = bms_add_member(entry->requests[forknum], (int) segno); MemoryContextSwitchTo(oldcxt); } } /* * ForgetRelationFsyncRequests -- forget any fsyncs for a relation fork * * forknum == InvalidForkNumber means all forks, although this code doesn't * actually know that, since it's just forwarding the request elsewhere. */ void ForgetRelationFsyncRequests(RelFileNode rnode, ForkNumber forknum) { if (pendingOpsTable) { /* standalone backend or startup process: fsync state is local */ RememberFsyncRequest(rnode, forknum, FORGET_RELATION_FSYNC); } else if (IsUnderPostmaster) { /* * Notify the checkpointer about it. If we fail to queue the cancel * message, we have to sleep and try again ... ugly, but hopefully * won't happen often. * * XXX should we CHECK_FOR_INTERRUPTS in this loop? Escaping with an * error would leave the no-longer-used file still present on disk, * which would be bad, so I'm inclined to assume that the checkpointer * will always empty the queue soon. */ while (!ForwardFsyncRequest(rnode, forknum, FORGET_RELATION_FSYNC)) pg_usleep(10000L); /* 10 msec seems a good number */ /* * Note we don't wait for the checkpointer to actually absorb the * cancel message; see mdsync() for the implications. */ } } /* * ForgetDatabaseFsyncRequests -- forget any fsyncs and unlinks for a DB */ void ForgetDatabaseFsyncRequests(Oid dbid) { RelFileNode rnode; rnode.dbNode = dbid; rnode.spcNode = 0; rnode.relNode = 0; if (pendingOpsTable) { /* standalone backend or startup process: fsync state is local */ RememberFsyncRequest(rnode, InvalidForkNumber, FORGET_DATABASE_FSYNC); } else if (IsUnderPostmaster) { /* see notes in ForgetRelationFsyncRequests */ while (!ForwardFsyncRequest(rnode, InvalidForkNumber, FORGET_DATABASE_FSYNC)) pg_usleep(10000L); /* 10 msec seems a good number */ } } /* * _fdvec_alloc() -- Make a MdfdVec object. */ static MdfdVec * _fdvec_alloc(void) { return (MdfdVec *) MemoryContextAlloc(MdCxt, sizeof(MdfdVec)); } /* * Return the filename for the specified segment of the relation. The * returned string is palloc'd. */ static char * _mdfd_segpath(SMgrRelation reln, ForkNumber forknum, BlockNumber segno) { char *path, *fullpath; path = relpath(reln->smgr_rnode, forknum); if (segno > 0) { fullpath = psprintf("%s.%u", path, segno); pfree(path); } else fullpath = path; return fullpath; } /* * Open the specified segment of the relation, * and make a MdfdVec object for it. Returns NULL on failure. */ static MdfdVec * _mdfd_openseg(SMgrRelation reln, ForkNumber forknum, BlockNumber segno, int oflags) { MdfdVec *v; int fd; char *fullpath; fullpath = _mdfd_segpath(reln, forknum, segno); /* open the file */ fd = PathNameOpenFile(fullpath, O_RDWR | PG_BINARY | oflags, 0600); pfree(fullpath); if (fd < 0) return NULL; /* allocate an mdfdvec entry for it */ v = _fdvec_alloc(); /* fill the entry */ v->mdfd_vfd = fd; v->mdfd_segno = segno; v->mdfd_chain = NULL; Assert(_mdnblocks(reln, forknum, v) <= ((BlockNumber) RELSEG_SIZE)); /* all done */ return v; } /* * _mdfd_getseg() -- Find the segment of the relation holding the * specified block. * * If the segment doesn't exist, we ereport, return NULL, or create the * segment, according to "behavior". Note: skipFsync is only used in the * EXTENSION_CREATE case. */ static MdfdVec * _mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno, bool skipFsync, ExtensionBehavior behavior) { MdfdVec *v = mdopen(reln, forknum, behavior); BlockNumber targetseg; BlockNumber nextsegno; if (!v) return NULL; /* only possible if EXTENSION_RETURN_NULL */ targetseg = blkno / ((BlockNumber) RELSEG_SIZE); for (nextsegno = 1; nextsegno <= targetseg; nextsegno++) { Assert(nextsegno == v->mdfd_segno + 1); if (v->mdfd_chain == NULL) { /* * Normally we will create new segments only if authorized by the * caller (i.e., we are doing mdextend()). But when doing WAL * recovery, create segments anyway; this allows cases such as * replaying WAL data that has a write into a high-numbered * segment of a relation that was later deleted. We want to go * ahead and create the segments so we can finish out the replay. * * We have to maintain the invariant that segments before the last * active segment are of size RELSEG_SIZE; therefore, pad them out * with zeroes if needed. (This only matters if caller is * extending the relation discontiguously, but that can happen in * hash indexes.) */ if (behavior == EXTENSION_CREATE || InRecovery) { if (_mdnblocks(reln, forknum, v) < RELSEG_SIZE) { char *zerobuf = palloc0(BLCKSZ); mdextend(reln, forknum, nextsegno * ((BlockNumber) RELSEG_SIZE) - 1, zerobuf, skipFsync); pfree(zerobuf); } v->mdfd_chain = _mdfd_openseg(reln, forknum, +nextsegno, O_CREAT); } else { /* We won't create segment if not existent */ v->mdfd_chain = _mdfd_openseg(reln, forknum, nextsegno, 0); } if (v->mdfd_chain == NULL) { if (behavior == EXTENSION_RETURN_NULL && FILE_POSSIBLY_DELETED(errno)) return NULL; ereport(ERROR, (errcode_for_file_access(), errmsg("could not open file \"%s\" (target block %u): %m", _mdfd_segpath(reln, forknum, nextsegno), blkno))); } } v = v->mdfd_chain; } return v; } /* * Get number of blocks present in a single disk file */ static BlockNumber _mdnblocks(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg) { off_t len; len = FileSeek(seg->mdfd_vfd, 0L, SEEK_END); if (len < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not seek to end of file \"%s\": %m", FilePathName(seg->mdfd_vfd)))); /* note that this calculation will ignore any partial block at EOF */ return (BlockNumber) (len / BLCKSZ); }