/*---------------------------------------------------------------------- * * tableam.c * Table access method routines too big to be inline functions. * * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/access/table/tableam.c * * NOTES * Note that most function in here are documented in tableam.h, rather than * here. That's because there's a lot of inline functions in tableam.h and * it'd be harder to understand if one constantly had to switch between files. * *---------------------------------------------------------------------- */ #include "postgres.h" #include #include "access/syncscan.h" #include "access/tableam.h" #include "access/xact.h" #include "optimizer/plancat.h" #include "port/pg_bitutils.h" #include "storage/bufmgr.h" #include "storage/shmem.h" #include "storage/smgr.h" /* * Constants to control the behavior of block allocation to parallel workers * during a parallel seqscan. Technically these values do not need to be * powers of 2, but having them as powers of 2 makes the math more optimal * and makes the ramp-down stepping more even. */ /* The number of I/O chunks we try to break a parallel seqscan down into */ #define PARALLEL_SEQSCAN_NCHUNKS 2048 /* Ramp down size of allocations when we've only this number of chunks left */ #define PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS 64 /* Cap the size of parallel I/O chunks to this number of blocks */ #define PARALLEL_SEQSCAN_MAX_CHUNK_SIZE 8192 /* GUC variables */ char *default_table_access_method = DEFAULT_TABLE_ACCESS_METHOD; bool synchronize_seqscans = true; /* ---------------------------------------------------------------------------- * Slot functions. * ---------------------------------------------------------------------------- */ const TupleTableSlotOps * table_slot_callbacks(Relation relation) { const TupleTableSlotOps *tts_cb; if (relation->rd_tableam) tts_cb = relation->rd_tableam->slot_callbacks(relation); else if (relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE) { /* * Historically FDWs expect to store heap tuples in slots. Continue * handing them one, to make it less painful to adapt FDWs to new * versions. The cost of a heap slot over a virtual slot is pretty * small. */ tts_cb = &TTSOpsHeapTuple; } else { /* * These need to be supported, as some parts of the code (like COPY) * need to create slots for such relations too. It seems better to * centralize the knowledge that a heap slot is the right thing in * that case here. */ Assert(relation->rd_rel->relkind == RELKIND_VIEW || relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE); tts_cb = &TTSOpsVirtual; } return tts_cb; } TupleTableSlot * table_slot_create(Relation relation, List **reglist) { const TupleTableSlotOps *tts_cb; TupleTableSlot *slot; tts_cb = table_slot_callbacks(relation); slot = MakeSingleTupleTableSlot(RelationGetDescr(relation), tts_cb); if (reglist) *reglist = lappend(*reglist, slot); return slot; } /* ---------------------------------------------------------------------------- * Table scan functions. * ---------------------------------------------------------------------------- */ TableScanDesc table_beginscan_catalog(Relation relation, int nkeys, struct ScanKeyData *key) { uint32 flags = SO_TYPE_SEQSCAN | SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE | SO_TEMP_SNAPSHOT; Oid relid = RelationGetRelid(relation); Snapshot snapshot = RegisterSnapshot(GetCatalogSnapshot(relid)); return relation->rd_tableam->scan_begin(relation, snapshot, nkeys, key, NULL, flags); } void table_scan_update_snapshot(TableScanDesc scan, Snapshot snapshot) { Assert(IsMVCCSnapshot(snapshot)); RegisterSnapshot(snapshot); scan->rs_snapshot = snapshot; scan->rs_flags |= SO_TEMP_SNAPSHOT; } /* ---------------------------------------------------------------------------- * Parallel table scan related functions. * ---------------------------------------------------------------------------- */ Size table_parallelscan_estimate(Relation rel, Snapshot snapshot) { Size sz = 0; if (IsMVCCSnapshot(snapshot)) sz = add_size(sz, EstimateSnapshotSpace(snapshot)); else Assert(snapshot == SnapshotAny); sz = add_size(sz, rel->rd_tableam->parallelscan_estimate(rel)); return sz; } void table_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan, Snapshot snapshot) { Size snapshot_off = rel->rd_tableam->parallelscan_initialize(rel, pscan); pscan->phs_snapshot_off = snapshot_off; if (IsMVCCSnapshot(snapshot)) { SerializeSnapshot(snapshot, (char *) pscan + pscan->phs_snapshot_off); pscan->phs_snapshot_any = false; } else { Assert(snapshot == SnapshotAny); pscan->phs_snapshot_any = true; } } TableScanDesc table_beginscan_parallel(Relation relation, ParallelTableScanDesc parallel_scan) { Snapshot snapshot; uint32 flags = SO_TYPE_SEQSCAN | SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE; Assert(RelationGetRelid(relation) == parallel_scan->phs_relid); if (!parallel_scan->phs_snapshot_any) { /* Snapshot was serialized -- restore it */ snapshot = RestoreSnapshot((char *) parallel_scan + parallel_scan->phs_snapshot_off); RegisterSnapshot(snapshot); flags |= SO_TEMP_SNAPSHOT; } else { /* SnapshotAny passed by caller (not serialized) */ snapshot = SnapshotAny; } return relation->rd_tableam->scan_begin(relation, snapshot, 0, NULL, parallel_scan, flags); } /* ---------------------------------------------------------------------------- * Index scan related functions. * ---------------------------------------------------------------------------- */ /* * To perform that check simply start an index scan, create the necessary * slot, do the heap lookup, and shut everything down again. This could be * optimized, but is unlikely to matter from a performance POV. If there * frequently are live index pointers also matching a unique index key, the * CPU overhead of this routine is unlikely to matter. * * Note that *tid may be modified when we return true if the AM supports * storing multiple row versions reachable via a single index entry (like * heap's HOT). */ bool table_index_fetch_tuple_check(Relation rel, ItemPointer tid, Snapshot snapshot, bool *all_dead) { IndexFetchTableData *scan; TupleTableSlot *slot; bool call_again = false; bool found; slot = table_slot_create(rel, NULL); scan = table_index_fetch_begin(rel); found = table_index_fetch_tuple(scan, tid, snapshot, slot, &call_again, all_dead); table_index_fetch_end(scan); ExecDropSingleTupleTableSlot(slot); return found; } /* ------------------------------------------------------------------------ * Functions for non-modifying operations on individual tuples * ------------------------------------------------------------------------ */ void table_tuple_get_latest_tid(TableScanDesc scan, ItemPointer tid) { Relation rel = scan->rs_rd; const TableAmRoutine *tableam = rel->rd_tableam; /* * We don't expect direct calls to table_tuple_get_latest_tid with valid * CheckXidAlive for catalog or regular tables. See detailed comments in * xact.c where these variables are declared. */ if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan)) elog(ERROR, "unexpected table_tuple_get_latest_tid call during logical decoding"); /* * Since this can be called with user-supplied TID, don't trust the input * too much. */ if (!tableam->tuple_tid_valid(scan, tid)) ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("tid (%u, %u) is not valid for relation \"%s\"", ItemPointerGetBlockNumberNoCheck(tid), ItemPointerGetOffsetNumberNoCheck(tid), RelationGetRelationName(rel)))); tableam->tuple_get_latest_tid(scan, tid); } /* ---------------------------------------------------------------------------- * Functions to make modifications a bit simpler. * ---------------------------------------------------------------------------- */ /* * simple_table_tuple_insert - insert a tuple * * Currently, this routine differs from table_tuple_insert only in supplying a * default command ID and not allowing access to the speedup options. */ void simple_table_tuple_insert(Relation rel, TupleTableSlot *slot) { table_tuple_insert(rel, slot, GetCurrentCommandId(true), 0, NULL); } /* * simple_table_tuple_delete - delete a tuple * * This routine may be used to delete a tuple when concurrent updates of * the target tuple are not expected (for example, because we have a lock * on the relation associated with the tuple). Any failure is reported * via ereport(). */ void simple_table_tuple_delete(Relation rel, ItemPointer tid, Snapshot snapshot) { TM_Result result; TM_FailureData tmfd; result = table_tuple_delete(rel, tid, GetCurrentCommandId(true), snapshot, InvalidSnapshot, true /* wait for commit */ , &tmfd, false /* changingPart */ ); switch (result) { case TM_SelfModified: /* Tuple was already updated in current command? */ elog(ERROR, "tuple already updated by self"); break; case TM_Ok: /* done successfully */ break; case TM_Updated: elog(ERROR, "tuple concurrently updated"); break; case TM_Deleted: elog(ERROR, "tuple concurrently deleted"); break; default: elog(ERROR, "unrecognized table_tuple_delete status: %u", result); break; } } /* * simple_table_tuple_update - replace a tuple * * This routine may be used to update a tuple when concurrent updates of * the target tuple are not expected (for example, because we have a lock * on the relation associated with the tuple). Any failure is reported * via ereport(). */ void simple_table_tuple_update(Relation rel, ItemPointer otid, TupleTableSlot *slot, Snapshot snapshot, bool *update_indexes) { TM_Result result; TM_FailureData tmfd; LockTupleMode lockmode; result = table_tuple_update(rel, otid, slot, GetCurrentCommandId(true), snapshot, InvalidSnapshot, true /* wait for commit */ , &tmfd, &lockmode, update_indexes); switch (result) { case TM_SelfModified: /* Tuple was already updated in current command? */ elog(ERROR, "tuple already updated by self"); break; case TM_Ok: /* done successfully */ break; case TM_Updated: elog(ERROR, "tuple concurrently updated"); break; case TM_Deleted: elog(ERROR, "tuple concurrently deleted"); break; default: elog(ERROR, "unrecognized table_tuple_update status: %u", result); break; } } /* ---------------------------------------------------------------------------- * Helper functions to implement parallel scans for block oriented AMs. * ---------------------------------------------------------------------------- */ Size table_block_parallelscan_estimate(Relation rel) { return sizeof(ParallelBlockTableScanDescData); } Size table_block_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan) { ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan; bpscan->base.phs_relid = RelationGetRelid(rel); bpscan->phs_nblocks = RelationGetNumberOfBlocks(rel); /* compare phs_syncscan initialization to similar logic in initscan */ bpscan->base.phs_syncscan = synchronize_seqscans && !RelationUsesLocalBuffers(rel) && bpscan->phs_nblocks > NBuffers / 4; SpinLockInit(&bpscan->phs_mutex); bpscan->phs_startblock = InvalidBlockNumber; pg_atomic_init_u64(&bpscan->phs_nallocated, 0); return sizeof(ParallelBlockTableScanDescData); } void table_block_parallelscan_reinitialize(Relation rel, ParallelTableScanDesc pscan) { ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan; pg_atomic_write_u64(&bpscan->phs_nallocated, 0); } /* * find and set the scan's startblock * * Determine where the parallel seq scan should start. This function may be * called many times, once by each parallel worker. We must be careful only * to set the startblock once. */ void table_block_parallelscan_startblock_init(Relation rel, ParallelBlockTableScanWorker pbscanwork, ParallelBlockTableScanDesc pbscan) { BlockNumber sync_startpage = InvalidBlockNumber; /* Reset the state we use for controlling allocation size. */ memset(pbscanwork, 0, sizeof(*pbscanwork)); StaticAssertStmt(MaxBlockNumber <= 0xFFFFFFFE, "pg_nextpower2_32 may be too small for non-standard BlockNumber width"); /* * We determine the chunk size based on the size of the relation. First we * split the relation into PARALLEL_SEQSCAN_NCHUNKS chunks but we then * take the next highest power of 2 number of the chunk size. This means * we split the relation into somewhere between PARALLEL_SEQSCAN_NCHUNKS * and PARALLEL_SEQSCAN_NCHUNKS / 2 chunks. */ pbscanwork->phsw_chunk_size = pg_nextpower2_32(Max(pbscan->phs_nblocks / PARALLEL_SEQSCAN_NCHUNKS, 1)); /* * Ensure we don't go over the maximum chunk size with larger tables. This * means we may get much more than PARALLEL_SEQSCAN_NCHUNKS for larger * tables. Too large a chunk size has been shown to be detrimental to * synchronous scan performance. */ pbscanwork->phsw_chunk_size = Min(pbscanwork->phsw_chunk_size, PARALLEL_SEQSCAN_MAX_CHUNK_SIZE); retry: /* Grab the spinlock. */ SpinLockAcquire(&pbscan->phs_mutex); /* * If the scan's startblock has not yet been initialized, we must do so * now. If this is not a synchronized scan, we just start at block 0, but * if it is a synchronized scan, we must get the starting position from * the synchronized scan machinery. We can't hold the spinlock while * doing that, though, so release the spinlock, get the information we * need, and retry. If nobody else has initialized the scan in the * meantime, we'll fill in the value we fetched on the second time * through. */ if (pbscan->phs_startblock == InvalidBlockNumber) { if (!pbscan->base.phs_syncscan) pbscan->phs_startblock = 0; else if (sync_startpage != InvalidBlockNumber) pbscan->phs_startblock = sync_startpage; else { SpinLockRelease(&pbscan->phs_mutex); sync_startpage = ss_get_location(rel, pbscan->phs_nblocks); goto retry; } } SpinLockRelease(&pbscan->phs_mutex); } /* * get the next page to scan * * Get the next page to scan. Even if there are no pages left to scan, * another backend could have grabbed a page to scan and not yet finished * looking at it, so it doesn't follow that the scan is done when the first * backend gets an InvalidBlockNumber return. */ BlockNumber table_block_parallelscan_nextpage(Relation rel, ParallelBlockTableScanWorker pbscanwork, ParallelBlockTableScanDesc pbscan) { BlockNumber page; uint64 nallocated; /* * The logic below allocates block numbers out to parallel workers in a * way that each worker will receive a set of consecutive block numbers to * scan. Earlier versions of this would allocate the next highest block * number to the next worker to call this function. This would generally * result in workers never receiving consecutive block numbers. Some * operating systems would not detect the sequential I/O pattern due to * each backend being a different process which could result in poor * performance due to inefficient or no readahead. To work around this * issue, we now allocate a range of block numbers for each worker and * when they come back for another block, we give them the next one in * that range until the range is complete. When the worker completes the * range of blocks we then allocate another range for it and return the * first block number from that range. * * Here we name these ranges of blocks "chunks". The initial size of * these chunks is determined in table_block_parallelscan_startblock_init * based on the size of the relation. Towards the end of the scan, we * start making reductions in the size of the chunks in order to attempt * to divide the remaining work over all the workers as evenly as * possible. * * Here pbscanwork is local worker memory. phsw_chunk_remaining tracks * the number of blocks remaining in the chunk. When that reaches 0 then * we must allocate a new chunk for the worker. * * phs_nallocated tracks how many blocks have been allocated to workers * already. When phs_nallocated >= rs_nblocks, all blocks have been * allocated. * * Because we use an atomic fetch-and-add to fetch the current value, the * phs_nallocated counter will exceed rs_nblocks, because workers will * still increment the value, when they try to allocate the next block but * all blocks have been allocated already. The counter must be 64 bits * wide because of that, to avoid wrapping around when rs_nblocks is close * to 2^32. * * The actual block to return is calculated by adding the counter to the * starting block number, modulo nblocks. */ /* * First check if we have any remaining blocks in a previous chunk for * this worker. We must consume all of the blocks from that before we * allocate a new chunk to the worker. */ if (pbscanwork->phsw_chunk_remaining > 0) { /* * Give them the next block in the range and update the remaining * number of blocks. */ nallocated = ++pbscanwork->phsw_nallocated; pbscanwork->phsw_chunk_remaining--; } else { /* * When we've only got PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS chunks * remaining in the scan, we half the chunk size. Since we reduce the * chunk size here, we'll hit this again after doing * PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS at the new size. After a few * iterations of this, we'll end up doing the last few blocks with the * chunk size set to 1. */ if (pbscanwork->phsw_chunk_size > 1 && pbscanwork->phsw_nallocated > pbscan->phs_nblocks - (pbscanwork->phsw_chunk_size * PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS)) pbscanwork->phsw_chunk_size >>= 1; nallocated = pbscanwork->phsw_nallocated = pg_atomic_fetch_add_u64(&pbscan->phs_nallocated, pbscanwork->phsw_chunk_size); /* * Set the remaining number of blocks in this chunk so that subsequent * calls from this worker continue on with this chunk until it's done. */ pbscanwork->phsw_chunk_remaining = pbscanwork->phsw_chunk_size - 1; } if (nallocated >= pbscan->phs_nblocks) page = InvalidBlockNumber; /* all blocks have been allocated */ else page = (nallocated + pbscan->phs_startblock) % pbscan->phs_nblocks; /* * Report scan location. Normally, we report the current page number. * When we reach the end of the scan, though, we report the starting page, * not the ending page, just so the starting positions for later scans * doesn't slew backwards. We only report the position at the end of the * scan once, though: subsequent callers will report nothing. */ if (pbscan->base.phs_syncscan) { if (page != InvalidBlockNumber) ss_report_location(rel, page); else if (nallocated == pbscan->phs_nblocks) ss_report_location(rel, pbscan->phs_startblock); } return page; } /* ---------------------------------------------------------------------------- * Helper functions to implement relation sizing for block oriented AMs. * ---------------------------------------------------------------------------- */ /* * table_block_relation_size * * If a table AM uses the various relation forks as the sole place where data * is stored, and if it uses them in the expected manner (e.g. the actual data * is in the main fork rather than some other), it can use this implementation * of the relation_size callback rather than implementing its own. */ uint64 table_block_relation_size(Relation rel, ForkNumber forkNumber) { uint64 nblocks = 0; /* Open it at the smgr level if not already done */ RelationOpenSmgr(rel); /* InvalidForkNumber indicates returning the size for all forks */ if (forkNumber == InvalidForkNumber) { for (int i = 0; i < MAX_FORKNUM; i++) nblocks += smgrnblocks(rel->rd_smgr, i); } else nblocks = smgrnblocks(rel->rd_smgr, forkNumber); return nblocks * BLCKSZ; } /* * table_block_relation_estimate_size * * This function can't be directly used as the implementation of the * relation_estimate_size callback, because it has a few additional parameters. * Instead, it is intended to be used as a helper function; the caller can * pass through the arguments to its relation_estimate_size function plus the * additional values required here. * * overhead_bytes_per_tuple should contain the approximate number of bytes * of storage required to store a tuple above and beyond what is required for * the tuple data proper. Typically, this would include things like the * size of the tuple header and item pointer. This is only used for query * planning, so a table AM where the value is not constant could choose to * pass a "best guess". * * usable_bytes_per_page should contain the approximate number of bytes per * page usable for tuple data, excluding the page header and any anticipated * special space. */ void table_block_relation_estimate_size(Relation rel, int32 *attr_widths, BlockNumber *pages, double *tuples, double *allvisfrac, Size overhead_bytes_per_tuple, Size usable_bytes_per_page) { BlockNumber curpages; BlockNumber relpages; double reltuples; BlockNumber relallvisible; double density; /* it should have storage, so we can call the smgr */ curpages = RelationGetNumberOfBlocks(rel); /* coerce values in pg_class to more desirable types */ relpages = (BlockNumber) rel->rd_rel->relpages; reltuples = (double) rel->rd_rel->reltuples; relallvisible = (BlockNumber) rel->rd_rel->relallvisible; /* * HACK: if the relation has never yet been vacuumed, use a minimum size * estimate of 10 pages. The idea here is to avoid assuming a * newly-created table is really small, even if it currently is, because * that may not be true once some data gets loaded into it. Once a vacuum * or analyze cycle has been done on it, it's more reasonable to believe * the size is somewhat stable. * * (Note that this is only an issue if the plan gets cached and used again * after the table has been filled. What we're trying to avoid is using a * nestloop-type plan on a table that has grown substantially since the * plan was made. Normally, autovacuum/autoanalyze will occur once enough * inserts have happened and cause cached-plan invalidation; but that * doesn't happen instantaneously, and it won't happen at all for cases * such as temporary tables.) * * We test "never vacuumed" by seeing whether reltuples < 0. * * If the table has inheritance children, we don't apply this heuristic. * Totally empty parent tables are quite common, so we should be willing * to believe that they are empty. */ if (curpages < 10 && reltuples < 0 && !rel->rd_rel->relhassubclass) curpages = 10; /* report estimated # pages */ *pages = curpages; /* quick exit if rel is clearly empty */ if (curpages == 0) { *tuples = 0; *allvisfrac = 0; return; } /* estimate number of tuples from previous tuple density */ if (reltuples >= 0 && relpages > 0) density = reltuples / (double) relpages; else { /* * When we have no data because the relation was never yet vacuumed, * estimate tuple width from attribute datatypes. We assume here that * the pages are completely full, which is OK for tables but is * probably an overestimate for indexes. Fortunately * get_relation_info() can clamp the overestimate to the parent * table's size. * * Note: this code intentionally disregards alignment considerations, * because (a) that would be gilding the lily considering how crude * the estimate is, (b) it creates platform dependencies in the * default plans which are kind of a headache for regression testing, * and (c) different table AMs might use different padding schemes. */ int32 tuple_width; tuple_width = get_rel_data_width(rel, attr_widths); tuple_width += overhead_bytes_per_tuple; /* note: integer division is intentional here */ density = usable_bytes_per_page / tuple_width; } *tuples = rint(density * (double) curpages); /* * We use relallvisible as-is, rather than scaling it up like we do for * the pages and tuples counts, on the theory that any pages added since * the last VACUUM are most likely not marked all-visible. But costsize.c * wants it converted to a fraction. */ if (relallvisible == 0 || curpages <= 0) *allvisfrac = 0; else if ((double) relallvisible >= curpages) *allvisfrac = 1; else *allvisfrac = (double) relallvisible / curpages; }