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Simplify autovacuum work-item implementation
The initial implementation of autovacuum work-items used a dynamic shared memory area (DSA). However, it's argued that dynamic shared memory is not portable enough, so we cannot rely on it being supported everywhere; at the same time, autovacuum work-items are now a critical part of the server, so it's not acceptable that they don't work in the cases where dynamic shared memory is disabled. Therefore, let's fall back to a simpler implementation of work-items that just uses autovacuum's main shared memory segment for storage. Discussion: https://postgr.es/m/CA+TgmobQVbz4K_+RSmiM9HeRKpy3vS5xnbkL95gSEnWijzprKQ@mail.gmail.com
This commit is contained in:
Alvaro Herrera
parent
b73f1b5c29
commit
31ae1638ce
@ -245,6 +245,24 @@ typedef enum
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AutoVacNumSignals /* must be last */
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} AutoVacuumSignal;
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/*
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* Autovacuum workitem array, stored in AutoVacuumShmem->av_workItems. This
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* list is mostly protected by AutovacuumLock, except that if an item is
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* marked 'active' other processes must not modify the work-identifying
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* members.
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*/
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typedef struct AutoVacuumWorkItem
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{
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AutoVacuumWorkItemType avw_type;
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bool avw_used; /* below data is valid */
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bool avw_active; /* being processed */
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Oid avw_database;
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Oid avw_relation;
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BlockNumber avw_blockNumber;
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} AutoVacuumWorkItem;
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#define NUM_WORKITEMS 256
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/*-------------
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* The main autovacuum shmem struct. On shared memory we store this main
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* struct and the array of WorkerInfo structs. This struct keeps:
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@ -255,10 +273,10 @@ typedef enum
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* av_runningWorkers the WorkerInfo non-free queue
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* av_startingWorker pointer to WorkerInfo currently being started (cleared by
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* the worker itself as soon as it's up and running)
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* av_dsa_handle handle for allocatable shared memory
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* av_workItems work item array
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*
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* This struct is protected by AutovacuumLock, except for av_signal and parts
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* of the worker list (see above). av_dsa_handle is readable unlocked.
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* of the worker list (see above).
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*-------------
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*/
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typedef struct
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@ -268,8 +286,7 @@ typedef struct
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dlist_head av_freeWorkers;
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dlist_head av_runningWorkers;
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WorkerInfo av_startingWorker;
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dsa_handle av_dsa_handle;
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dsa_pointer av_workitems;
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AutoVacuumWorkItem av_workItems[NUM_WORKITEMS];
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} AutoVacuumShmemStruct;
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static AutoVacuumShmemStruct *AutoVacuumShmem;
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@ -284,32 +301,6 @@ static MemoryContext DatabaseListCxt = NULL;
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/* Pointer to my own WorkerInfo, valid on each worker */
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static WorkerInfo MyWorkerInfo = NULL;
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/*
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* Autovacuum workitem array, stored in AutoVacuumShmem->av_workitems. This
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* list is mostly protected by AutovacuumLock, except that if it's marked
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* 'active' other processes must not modify the work-identifying members,
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* though changing the list pointers is okay.
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*/
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typedef struct AutoVacuumWorkItem
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{
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AutoVacuumWorkItemType avw_type;
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Oid avw_database;
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Oid avw_relation;
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BlockNumber avw_blockNumber;
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bool avw_active;
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dsa_pointer avw_next; /* doubly linked list pointers */
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dsa_pointer avw_prev;
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} AutoVacuumWorkItem;
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#define NUM_WORKITEMS 256
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typedef struct
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{
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dsa_pointer avs_usedItems;
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dsa_pointer avs_freeItems;
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} AutovacWorkItems;
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static dsa_area *AutoVacuumDSA = NULL;
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/* PID of launcher, valid only in worker while shutting down */
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int AutovacuumLauncherPid = 0;
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@ -356,8 +347,6 @@ static void av_sighup_handler(SIGNAL_ARGS);
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static void avl_sigusr2_handler(SIGNAL_ARGS);
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static void avl_sigterm_handler(SIGNAL_ARGS);
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static void autovac_refresh_stats(void);
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static void remove_wi_from_list(dsa_pointer *list, dsa_pointer wi_ptr);
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static void add_wi_to_list(dsa_pointer *list, dsa_pointer wi_ptr);
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@ -631,29 +620,6 @@ AutoVacLauncherMain(int argc, char *argv[])
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*/
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rebuild_database_list(InvalidOid);
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/*
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* Set up our DSA so that backends can install work-item requests. It may
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* already exist as created by a previous launcher; and we may even be
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* already attached to it, if we're here after longjmp'ing above.
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*/
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if (!AutoVacuumShmem->av_dsa_handle)
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{
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LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
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AutoVacuumDSA = dsa_create(AutovacuumLock->tranche);
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/* make sure it doesn't go away even if we do */
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dsa_pin(AutoVacuumDSA);
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dsa_pin_mapping(AutoVacuumDSA);
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AutoVacuumShmem->av_dsa_handle = dsa_get_handle(AutoVacuumDSA);
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/* delay array allocation until first request */
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AutoVacuumShmem->av_workitems = InvalidDsaPointer;
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LWLockRelease(AutovacuumLock);
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}
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else if (AutoVacuumDSA == NULL)
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{
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AutoVacuumDSA = dsa_attach(AutoVacuumShmem->av_dsa_handle);
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dsa_pin_mapping(AutoVacuumDSA);
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}
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/* loop until shutdown request */
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while (!got_SIGTERM)
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{
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@ -1697,14 +1663,6 @@ AutoVacWorkerMain(int argc, char *argv[])
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{
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char dbname[NAMEDATALEN];
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if (AutoVacuumShmem->av_dsa_handle)
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{
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/* First use of DSA in this worker, so attach to it */
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Assert(!AutoVacuumDSA);
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AutoVacuumDSA = dsa_attach(AutoVacuumShmem->av_dsa_handle);
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dsa_pin_mapping(AutoVacuumDSA);
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}
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/*
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* Report autovac startup to the stats collector. We deliberately do
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* this before InitPostgres, so that the last_autovac_time will get
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@ -1987,6 +1945,7 @@ do_autovacuum(void)
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int effective_multixact_freeze_max_age;
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bool did_vacuum = false;
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bool found_concurrent_worker = false;
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int i;
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/*
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* StartTransactionCommand and CommitTransactionCommand will automatically
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@ -2557,65 +2516,40 @@ deleted:
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/*
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* Perform additional work items, as requested by backends.
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*/
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if (AutoVacuumShmem->av_workitems)
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LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
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for (i = 0; i < NUM_WORKITEMS; i++)
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{
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dsa_pointer wi_ptr;
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AutovacWorkItems *workitems;
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AutoVacuumWorkItem *workitem = &AutoVacuumShmem->av_workItems[i];
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if (!workitem->avw_used)
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continue;
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if (workitem->avw_active)
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continue;
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/* claim this one, and release lock while performing it */
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workitem->avw_active = true;
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LWLockRelease(AutovacuumLock);
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perform_work_item(workitem);
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/*
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* Check for config changes before acquiring lock for further
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* jobs.
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*/
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CHECK_FOR_INTERRUPTS();
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if (got_SIGHUP)
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{
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got_SIGHUP = false;
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ProcessConfigFile(PGC_SIGHUP);
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}
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LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
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/*
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* Scan the list of pending items, and process the inactive ones in
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* our database.
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*/
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workitems = (AutovacWorkItems *)
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dsa_get_address(AutoVacuumDSA, AutoVacuumShmem->av_workitems);
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wi_ptr = workitems->avs_usedItems;
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while (wi_ptr != InvalidDsaPointer)
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{
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AutoVacuumWorkItem *workitem;
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workitem = (AutoVacuumWorkItem *)
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dsa_get_address(AutoVacuumDSA, wi_ptr);
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if (workitem->avw_database == MyDatabaseId && !workitem->avw_active)
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{
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dsa_pointer next_ptr;
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/* claim this one */
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workitem->avw_active = true;
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LWLockRelease(AutovacuumLock);
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perform_work_item(workitem);
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/*
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* Check for config changes before acquiring lock for further
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* jobs.
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*/
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CHECK_FOR_INTERRUPTS();
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if (got_SIGHUP)
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{
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got_SIGHUP = false;
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ProcessConfigFile(PGC_SIGHUP);
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}
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LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
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/* Put the array item back for the next user */
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next_ptr = workitem->avw_next;
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remove_wi_from_list(&workitems->avs_usedItems, wi_ptr);
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add_wi_to_list(&workitems->avs_freeItems, wi_ptr);
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wi_ptr = next_ptr;
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}
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else
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wi_ptr = workitem->avw_next;
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}
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/* all done */
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LWLockRelease(AutovacuumLock);
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/* and mark it done */
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workitem->avw_active = false;
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workitem->avw_used = false;
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}
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LWLockRelease(AutovacuumLock);
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/*
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* We leak table_toast_map here (among other things), but since we're
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@ -3252,104 +3186,32 @@ void
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AutoVacuumRequestWork(AutoVacuumWorkItemType type, Oid relationId,
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BlockNumber blkno)
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{
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AutovacWorkItems *workitems;
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dsa_pointer wi_ptr;
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AutoVacuumWorkItem *workitem;
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int i;
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LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
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/*
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* It may be useful to de-duplicate the list upon insertion. For the only
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* currently existing caller, this is not necessary.
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* Locate an unused work item and fill it with the given data.
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*/
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/* First use in this process? Set up DSA */
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if (!AutoVacuumDSA)
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for (i = 0; i < NUM_WORKITEMS; i++)
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{
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if (!AutoVacuumShmem->av_dsa_handle)
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{
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/* autovacuum launcher not started; nothing can be done */
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LWLockRelease(AutovacuumLock);
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return;
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}
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AutoVacuumDSA = dsa_attach(AutoVacuumShmem->av_dsa_handle);
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dsa_pin_mapping(AutoVacuumDSA);
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AutoVacuumWorkItem *workitem = &AutoVacuumShmem->av_workItems[i];
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if (workitem->avw_used)
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continue;
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workitem->avw_used = true;
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workitem->avw_active = false;
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workitem->avw_type = type;
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workitem->avw_database = MyDatabaseId;
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workitem->avw_relation = relationId;
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workitem->avw_blockNumber = blkno;
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/* done */
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break;
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}
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/* First use overall? Allocate work items array */
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if (AutoVacuumShmem->av_workitems == InvalidDsaPointer)
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{
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int i;
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AutovacWorkItems *workitems;
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AutoVacuumShmem->av_workitems =
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dsa_allocate_extended(AutoVacuumDSA,
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sizeof(AutovacWorkItems) +
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NUM_WORKITEMS * sizeof(AutoVacuumWorkItem),
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DSA_ALLOC_NO_OOM);
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/* if out of memory, silently disregard the request */
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if (AutoVacuumShmem->av_workitems == InvalidDsaPointer)
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{
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LWLockRelease(AutovacuumLock);
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dsa_detach(AutoVacuumDSA);
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AutoVacuumDSA = NULL;
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return;
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}
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/* Initialize each array entry as a member of the free list */
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workitems = dsa_get_address(AutoVacuumDSA, AutoVacuumShmem->av_workitems);
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workitems->avs_usedItems = InvalidDsaPointer;
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workitems->avs_freeItems = InvalidDsaPointer;
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for (i = 0; i < NUM_WORKITEMS; i++)
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{
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/* XXX surely there is a simpler way to do this */
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wi_ptr = AutoVacuumShmem->av_workitems + sizeof(AutovacWorkItems) +
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sizeof(AutoVacuumWorkItem) * i;
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workitem = (AutoVacuumWorkItem *) dsa_get_address(AutoVacuumDSA, wi_ptr);
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workitem->avw_type = 0;
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workitem->avw_database = InvalidOid;
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workitem->avw_relation = InvalidOid;
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workitem->avw_active = false;
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/* put this item in the free list */
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workitem->avw_next = workitems->avs_freeItems;
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workitems->avs_freeItems = wi_ptr;
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}
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}
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workitems = (AutovacWorkItems *)
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dsa_get_address(AutoVacuumDSA, AutoVacuumShmem->av_workitems);
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/* If array is full, disregard the request */
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if (workitems->avs_freeItems == InvalidDsaPointer)
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{
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LWLockRelease(AutovacuumLock);
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dsa_detach(AutoVacuumDSA);
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AutoVacuumDSA = NULL;
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return;
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}
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/* remove workitem struct from free list ... */
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wi_ptr = workitems->avs_freeItems;
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remove_wi_from_list(&workitems->avs_freeItems, wi_ptr);
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/* ... initialize it ... */
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workitem = dsa_get_address(AutoVacuumDSA, wi_ptr);
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workitem->avw_type = type;
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workitem->avw_database = MyDatabaseId;
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workitem->avw_relation = relationId;
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workitem->avw_blockNumber = blkno;
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workitem->avw_active = false;
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/* ... and put it on autovacuum's to-do list */
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add_wi_to_list(&workitems->avs_usedItems, wi_ptr);
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LWLockRelease(AutovacuumLock);
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dsa_detach(AutoVacuumDSA);
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AutoVacuumDSA = NULL;
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}
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/*
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@ -3429,6 +3291,8 @@ AutoVacuumShmemInit(void)
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dlist_init(&AutoVacuumShmem->av_freeWorkers);
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dlist_init(&AutoVacuumShmem->av_runningWorkers);
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AutoVacuumShmem->av_startingWorker = NULL;
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memset(AutoVacuumShmem->av_workItems, 0,
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sizeof(AutoVacuumWorkItem) * NUM_WORKITEMS);
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worker = (WorkerInfo) ((char *) AutoVacuumShmem +
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MAXALIGN(sizeof(AutoVacuumShmemStruct)));
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@ -3473,59 +3337,3 @@ autovac_refresh_stats(void)
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pgstat_clear_snapshot();
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}
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/*
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* Simplistic open-coded list implementation for objects stored in DSA.
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* Each item is doubly linked, but we have no tail pointer, and the "prev"
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* element of the first item is null, not the list.
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*/
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/*
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* Remove a work item from the given list.
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*/
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static void
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remove_wi_from_list(dsa_pointer *list, dsa_pointer wi_ptr)
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{
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AutoVacuumWorkItem *workitem = dsa_get_address(AutoVacuumDSA, wi_ptr);
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dsa_pointer next = workitem->avw_next;
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dsa_pointer prev = workitem->avw_prev;
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workitem->avw_next = workitem->avw_prev = InvalidDsaPointer;
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if (next != InvalidDsaPointer)
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{
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workitem = dsa_get_address(AutoVacuumDSA, next);
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workitem->avw_prev = prev;
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}
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if (prev != InvalidDsaPointer)
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{
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workitem = dsa_get_address(AutoVacuumDSA, prev);
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workitem->avw_next = next;
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}
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else
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*list = next;
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}
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/*
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* Add a workitem to the given list
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*/
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static void
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add_wi_to_list(dsa_pointer *list, dsa_pointer wi_ptr)
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{
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if (*list == InvalidDsaPointer)
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{
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/* list is empty; item is now singleton */
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*list = wi_ptr;
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}
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else
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{
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AutoVacuumWorkItem *workitem = dsa_get_address(AutoVacuumDSA, wi_ptr);
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AutoVacuumWorkItem *old = dsa_get_address(AutoVacuumDSA, *list);
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/* Put item at head of list */
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workitem->avw_next = *list;
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old->avw_prev = wi_ptr;
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*list = wi_ptr;
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}
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}
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