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355 lines
9.5 KiB
C
355 lines
9.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* sharedfileset.c
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* Shared temporary file management.
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*
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* Portions Copyright (c) 1996-2021, 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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* IDENTIFICATION
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* src/backend/storage/file/sharedfileset.c
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*
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* SharedFileSets provide a temporary namespace (think directory) so that
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* files can be discovered by name, and a shared ownership semantics so that
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* shared files survive until the last user detaches.
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*
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* SharedFileSets can be used by backends when the temporary files need to be
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* opened/closed multiple times and the underlying files need to survive across
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* transactions.
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <limits.h>
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#include "catalog/pg_tablespace.h"
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#include "commands/tablespace.h"
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#include "common/hashfn.h"
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#include "miscadmin.h"
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#include "storage/dsm.h"
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#include "storage/ipc.h"
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#include "storage/sharedfileset.h"
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#include "utils/builtins.h"
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static List *filesetlist = NIL;
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static void SharedFileSetOnDetach(dsm_segment *segment, Datum datum);
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static void SharedFileSetDeleteOnProcExit(int status, Datum arg);
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static void SharedFileSetPath(char *path, SharedFileSet *fileset, Oid tablespace);
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static void SharedFilePath(char *path, SharedFileSet *fileset, const char *name);
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static Oid ChooseTablespace(const SharedFileSet *fileset, const char *name);
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/*
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* Initialize a space for temporary files that can be opened by other backends.
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* Other backends must attach to it before accessing it. Associate this
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* SharedFileSet with 'seg'. Any contained files will be deleted when the
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* last backend detaches.
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*
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* We can also use this interface if the temporary files are used only by
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* single backend but the files need to be opened and closed multiple times
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* and also the underlying files need to survive across transactions. For
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* such cases, dsm segment 'seg' should be passed as NULL. Callers are
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* expected to explicitly remove such files by using SharedFileSetDelete/
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* SharedFileSetDeleteAll or we remove such files on proc exit.
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*
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* Files will be distributed over the tablespaces configured in
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* temp_tablespaces.
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*
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* Under the covers the set is one or more directories which will eventually
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* be deleted.
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*/
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void
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SharedFileSetInit(SharedFileSet *fileset, dsm_segment *seg)
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{
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static uint32 counter = 0;
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SpinLockInit(&fileset->mutex);
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fileset->refcnt = 1;
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fileset->creator_pid = MyProcPid;
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fileset->number = counter;
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counter = (counter + 1) % INT_MAX;
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/* Capture the tablespace OIDs so that all backends agree on them. */
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PrepareTempTablespaces();
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fileset->ntablespaces =
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GetTempTablespaces(&fileset->tablespaces[0],
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lengthof(fileset->tablespaces));
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if (fileset->ntablespaces == 0)
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{
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/* If the GUC is empty, use current database's default tablespace */
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fileset->tablespaces[0] = MyDatabaseTableSpace;
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fileset->ntablespaces = 1;
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}
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else
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{
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int i;
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/*
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* An entry of InvalidOid means use the default tablespace for the
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* current database. Replace that now, to be sure that all users of
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* the SharedFileSet agree on what to do.
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*/
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for (i = 0; i < fileset->ntablespaces; i++)
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{
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if (fileset->tablespaces[i] == InvalidOid)
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fileset->tablespaces[i] = MyDatabaseTableSpace;
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}
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}
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/* Register our cleanup callback. */
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if (seg)
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on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
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else
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{
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static bool registered_cleanup = false;
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if (!registered_cleanup)
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{
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/*
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* We must not have registered any fileset before registering the
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* fileset clean up.
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*/
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Assert(filesetlist == NIL);
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on_proc_exit(SharedFileSetDeleteOnProcExit, 0);
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registered_cleanup = true;
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}
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filesetlist = lcons((void *) fileset, filesetlist);
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}
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}
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/*
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* Attach to a set of directories that was created with SharedFileSetInit.
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*/
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void
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SharedFileSetAttach(SharedFileSet *fileset, dsm_segment *seg)
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{
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bool success;
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SpinLockAcquire(&fileset->mutex);
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if (fileset->refcnt == 0)
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success = false;
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else
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{
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++fileset->refcnt;
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success = true;
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}
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SpinLockRelease(&fileset->mutex);
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if (!success)
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ereport(ERROR,
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(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
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errmsg("could not attach to a SharedFileSet that is already destroyed")));
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/* Register our cleanup callback. */
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on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
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}
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/*
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* Create a new file in the given set.
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*/
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File
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SharedFileSetCreate(SharedFileSet *fileset, const char *name)
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{
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char path[MAXPGPATH];
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File file;
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SharedFilePath(path, fileset, name);
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file = PathNameCreateTemporaryFile(path, false);
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/* If we failed, see if we need to create the directory on demand. */
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if (file <= 0)
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{
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char tempdirpath[MAXPGPATH];
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char filesetpath[MAXPGPATH];
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Oid tablespace = ChooseTablespace(fileset, name);
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TempTablespacePath(tempdirpath, tablespace);
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SharedFileSetPath(filesetpath, fileset, tablespace);
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PathNameCreateTemporaryDir(tempdirpath, filesetpath);
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file = PathNameCreateTemporaryFile(path, true);
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}
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return file;
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}
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/*
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* Open a file that was created with SharedFileSetCreate(), possibly in
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* another backend.
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*/
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File
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SharedFileSetOpen(SharedFileSet *fileset, const char *name, int mode)
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{
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char path[MAXPGPATH];
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File file;
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SharedFilePath(path, fileset, name);
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file = PathNameOpenTemporaryFile(path, mode);
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return file;
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}
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/*
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* Delete a file that was created with SharedFileSetCreate().
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* Return true if the file existed, false if didn't.
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*/
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bool
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SharedFileSetDelete(SharedFileSet *fileset, const char *name,
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bool error_on_failure)
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{
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char path[MAXPGPATH];
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SharedFilePath(path, fileset, name);
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return PathNameDeleteTemporaryFile(path, error_on_failure);
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}
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/*
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* Delete all files in the set.
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*/
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void
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SharedFileSetDeleteAll(SharedFileSet *fileset)
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{
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char dirpath[MAXPGPATH];
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int i;
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/*
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* Delete the directory we created in each tablespace. Doesn't fail
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* because we use this in error cleanup paths, but can generate LOG
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* message on IO error.
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*/
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for (i = 0; i < fileset->ntablespaces; ++i)
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{
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SharedFileSetPath(dirpath, fileset, fileset->tablespaces[i]);
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PathNameDeleteTemporaryDir(dirpath);
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}
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/* Unregister the shared fileset */
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SharedFileSetUnregister(fileset);
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}
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/*
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* Callback function that will be invoked when this backend detaches from a
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* DSM segment holding a SharedFileSet that it has created or attached to. If
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* we are the last to detach, then try to remove the directories and
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* everything in them. We can't raise an error on failures, because this runs
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* in error cleanup paths.
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*/
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static void
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SharedFileSetOnDetach(dsm_segment *segment, Datum datum)
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{
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bool unlink_all = false;
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SharedFileSet *fileset = (SharedFileSet *) DatumGetPointer(datum);
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SpinLockAcquire(&fileset->mutex);
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Assert(fileset->refcnt > 0);
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if (--fileset->refcnt == 0)
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unlink_all = true;
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SpinLockRelease(&fileset->mutex);
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/*
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* If we are the last to detach, we delete the directory in all
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* tablespaces. Note that we are still actually attached for the rest of
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* this function so we can safely access its data.
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*/
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if (unlink_all)
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SharedFileSetDeleteAll(fileset);
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}
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/*
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* Callback function that will be invoked on the process exit. This will
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* process the list of all the registered sharedfilesets and delete the
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* underlying files.
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*/
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static void
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SharedFileSetDeleteOnProcExit(int status, Datum arg)
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{
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/*
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* Remove all the pending shared fileset entries. We don't use foreach() here
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* because SharedFileSetDeleteAll will remove the current element in
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* filesetlist. Though we have used foreach_delete_current() to remove the
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* element from filesetlist it could only fix up the state of one of the
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* loops, see SharedFileSetUnregister.
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*/
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while (list_length(filesetlist) > 0)
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{
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SharedFileSet *fileset = (SharedFileSet *) linitial(filesetlist);
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SharedFileSetDeleteAll(fileset);
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}
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filesetlist = NIL;
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}
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/*
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* Unregister the shared fileset entry registered for cleanup on proc exit.
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*/
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void
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SharedFileSetUnregister(SharedFileSet *input_fileset)
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{
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ListCell *l;
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/*
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* If the caller is following the dsm based cleanup then we don't maintain
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* the filesetlist so return.
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*/
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if (filesetlist == NIL)
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return;
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foreach(l, filesetlist)
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{
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SharedFileSet *fileset = (SharedFileSet *) lfirst(l);
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/* Remove the entry from the list */
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if (input_fileset == fileset)
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{
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filesetlist = foreach_delete_current(filesetlist, l);
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return;
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}
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}
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/* Should have found a match */
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Assert(false);
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}
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/*
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* Build the path for the directory holding the files backing a SharedFileSet
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* in a given tablespace.
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*/
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static void
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SharedFileSetPath(char *path, SharedFileSet *fileset, Oid tablespace)
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{
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char tempdirpath[MAXPGPATH];
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TempTablespacePath(tempdirpath, tablespace);
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snprintf(path, MAXPGPATH, "%s/%s%lu.%u.sharedfileset",
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tempdirpath, PG_TEMP_FILE_PREFIX,
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(unsigned long) fileset->creator_pid, fileset->number);
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}
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/*
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* Sorting hat to determine which tablespace a given shared temporary file
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* belongs in.
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*/
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static Oid
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ChooseTablespace(const SharedFileSet *fileset, const char *name)
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{
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uint32 hash = hash_any((const unsigned char *) name, strlen(name));
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return fileset->tablespaces[hash % fileset->ntablespaces];
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}
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/*
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* Compute the full path of a file in a SharedFileSet.
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*/
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static void
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SharedFilePath(char *path, SharedFileSet *fileset, const char *name)
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{
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char dirpath[MAXPGPATH];
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SharedFileSetPath(dirpath, fileset, ChooseTablespace(fileset, name));
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snprintf(path, MAXPGPATH, "%s/%s", dirpath, name);
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}
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