本节简单解释了PostgreSQL NOT IN在执行时写入临时表空间的实现。

测试数据如下：

[local]:5432 pg12@testdb=# select count(*) from tbl; count ------- 1(1 row)Time: 6.009 ms[local]:5432 pg12@testdb=# select count(*) from t_big_null; count ---------- 10000001(1 row)[local]:5432 pg12@testdb=#一、数据结构

Tuplestorestate
Tuplestore相关操作的私有状态。

/* * Possible states of a Tuplestore object. These denote the states that * persist between calls of Tuplestore routines. */typedef enum{ TSS_INMEM, /* Tuples still fit in memory */ TSS_WRITEFILE, /* Writing to temp file */ TSS_READFILE /* Reading from temp file */} TupStoreStatus;/* * Private state of a Tuplestore operation. */struct Tuplestorestate{ TupStoreStatus status; /* 状态枚举值；enumerated value as shown above */ int eflags; /* capability flags (OR of pointers' flags) */ bool backward; /* store extra length words in file? */ bool interXact; /* keep open through transactions? */ bool truncated; /* tuplestore_trim has removed tuples? */ int64 availMem; /* remaining memory available, in bytes */ int64 allowedMem; /* total memory allowed, in bytes */ int64 tuples; /* number of tuples added */ BufFile *myfile; /* underlying file, or NULL if none */ MemoryContext context; /* memory context for holding tuples */ ResourceOwner resowner; /* resowner for holding temp files */ /* * These function pointers decouple the routines that must know what kind * of tuple we are handling from the routines that don't need to know it. * They are set up by the tuplestore_begin_xxx routines. * * (Although tuplestore.c currently only supports heap tuples, I've copied * this part of tuplesort.c so that extension to other kinds of objects * will be easy if it's ever needed.) * * Function to copy a supplied input tuple into palloc'd space. (NB: we * assume that a single pfree() is enough to release the tuple later, so * the representation must be "flat" in one palloc chunk.) state->availMem * must be decreased by the amount of space used. */ void *(*copytup) (Tuplestorestate *state, void *tup); /* * Function to write a stored tuple onto tape. The representation of the * tuple on tape need not be the same as it is in memory; requirements on * the tape representation are given below. After writing the tuple, * pfree() it, and increase state->availMem by the amount of memory space * thereby released. */ void (*writetup) (Tuplestorestate *state, void *tup); /* * Function to read a stored tuple from tape back into memory. 'len' is * the already-read length of the stored tuple. Create and return a * palloc'd copy, and decrease state->availMem by the amount of memory * space consumed. */ void *(*readtup) (Tuplestorestate *state, unsigned int len); /* * This array holds pointers to tuples in memory if we are in state INMEM. * In states WRITEFILE and READFILE it's not used. * * When memtupdeleted > 0, the first memtupdeleted pointers are already * released due to a tuplestore_trim() operation, but we haven't expended * the effort to slide the remaining pointers down. These unused pointers * are set to NULL to catch any invalid accesses. Note that memtupcount * includes the deleted pointers. */ void **memtuples; /* array of pointers to palloc'd tuples */ int memtupdeleted; /* the first N slots are currently unused */ int memtupcount; /* number of tuples currently present */ int memtupsize; /* allocated length of memtuples array */ bool growmemtuples; /* memtuples' growth still underway? */ /* * These variables are used to keep track of the current positions. * * In state WRITEFILE, the current file seek position is the write point; * in state READFILE, the write position is remembered in writepos_xxx. * (The write position is the same as EOF, but since BufFileSeek doesn't * currently implement SEEK_END, we have to remember it explicitly.) */ TSReadPointer *readptrs; /* array of read pointers */ int activeptr; /* index of the active read pointer */ int readptrcount; /* number of pointers currently valid */ int readptrsize; /* allocated length of readptrs array */ int writepos_file; /* file# (valid if READFILE state) */ off_t writepos_offset; /* offset (valid if READFILE state) */};#define COPYTUP(state,tup) ((*(state)->copytup) (state, tup))#define WRITETUP(state,tup) ((*(state)->writetup) (state, tup))#define READTUP(state,len) ((*(state)->readtup) (state, len))#define LACKMEM(state) ((state)->availMem < 0)#define USEMEM(state,amt) ((state)->availMem -= (amt))#define FREEMEM(state,amt) ((state)->availMem += (amt))

TSReadPointer
tuplestore读指针

/* * Possible states of a Tuplestore object. These denote the states that * persist between calls of Tuplestore routines. */typedef enum{ TSS_INMEM, /* Tuples still fit in memory */ TSS_WRITEFILE, /* Writing to temp file */ TSS_READFILE /* Reading from temp file */} TupStoreStatus;/* * State for a single read pointer. If we are in state INMEM then all the * read pointers' "current" fields denote the read positions. In state * WRITEFILE, the file/offset fields denote the read positions. In state * READFILE, inactive read pointers have valid file/offset, but the active * read pointer implicitly has position equal to the temp file's seek position. * * Special case: if eof_reached is true, then the pointer's read position is * implicitly equal to the write position, and current/file/offset aren't * maintained. This way we need not update all the read pointers each time * we write. */typedef struct{ int eflags; /* capability flags */ bool eof_reached; /* read has reached EOF */ int current; /* next array index to read */ int file; /* temp file# */ off_t offset; /* byte offset in file */} TSReadPointer;

BufFile
该数据结构表示包含一个或多个物理文件的buffered file(每一个通过fd.c管理的虚拟文件描述符进行访问)

/* * We break BufFiles into gigabyte-sized segments, regardless of RELSEG_SIZE. * The reason is that we'd like large BufFiles to be spread across multiple * tablespaces when available. * BufFiles会拆分为以几个GB为单位的segments而不管RELSEG_SIZE的大小. * 原因是我们倾向于在可用时把很大的BufFiles在多个表空间中分布. */#define MAX_PHYSICAL_FILESIZE 0x40000000#define BUFFILE_SEG_SIZE (MAX_PHYSICAL_FILESIZE / BLCKSZ)/* * This data structure represents a buffered file that consists of one or * more physical files (each accessed through a virtual file descriptor * managed by fd.c). * 该数据结构表示包含一个或多个物理文件的buffered file(每一个通过fd.c管理的虚拟文件描述符进行访问) */struct BufFile{ //集合中物理文件的数量 int numFiles; /* number of physical files in set */ /* all files except the last have length exactly MAX_PHYSICAL_FILESIZE */ //------- 除了最后一个文件,其他文件的大小为MAX_PHYSICAL_FILESIZE //使用numFiles分配的数组 File *files; /* palloc'd array with numFiles entries */ //跨事务? bool isInterXact; /* keep open over transactions? */ //脏数据? bool dirty; /* does buffer need to be written? */ //是否只读? bool readOnly; /* has the file been set to read only? */ //如共享,段文件的空间大小 SharedFileSet *fileset; /* space for segment files if shared */ //如共享,该BufFile的名称 const char *name; /* name of this BufFile if shared */ /* * resowner is the ResourceOwner to use for underlying temp files. (We * don't need to remember the memory context we're using explicitly, * because after creation we only repalloc our arrays larger.) * 用于临时文件的ResourceOwner */ ResourceOwner resowner; /* * "current pos" is position of start of buffer within the logical file. * Position as seen by user of BufFile is (curFile, curOffset + pos). * "current pos" 是逻辑文件中buffer的起始位置. * BufFile用户看到的位置是((curFile, curOffset + pos)) */ //文件索引,当前位置的第(0..n)部分 int curFile; /* file index (0..n) part of current pos */ //当前位置的偏移部分 off_t curOffset; /* offset part of current pos */ //buffer中的下一个R/W位置 int pos; /* next read/write position in buffer */ //buffer中的有效字节数 int nbytes; /* total # of valid bytes in buffer */ PGAlignedBlock buffer;};二、源码解读

tuplestore_puttupleslot
把接收到的tuple放到tuplestore中

/* * Accept one tuple and append it to the tuplestore. * 把接收到的tuple放到tuplestore中 * * Note that the input tuple is always copied; the caller need not save it. * 要注意的是输入元组通常已被拷贝，调用者不需要存储该元组。 * * If the active read pointer is currently "at EOF", it remains so (the read * pointer implicitly advances along with the write pointer); otherwise the * read pointer is unchanged. Non-active read pointers do not move, which * means they are certain to not be "at EOF" immediately after puttuple. * This curious-seeming behavior is for the convenience of nodeMaterial.c and * nodeCtescan.c, which would otherwise need to do extra pointer repositioning * steps. * 如果活动的读指针当前正处于EOF位置，那么仍会保留现状（读指针默认与写指针同步）。 * 否则的话，读指针是不变的。非活动读指针不会移动，意味着在puttuple后没有马上就处于EOF状态下。 * 这种看似奇怪的行为是便于nodeMaterial.c和nodeCtescan.c的处理，否则需要额外的指针重定位。 * * tuplestore_puttupleslot() is a convenience routine to collect data from * a TupleTableSlot without an extra copy operation. * tuplestore_puttupleslot()例程不需要额外的拷贝动作从TupleTableSlot中收集数据。 */voidtuplestore_puttupleslot(Tuplestorestate *state, TupleTableSlot *slot){ MinimalTuple tuple; MemoryContext oldcxt = MemoryContextSwitchTo(state->context); /* * Form a MinimalTuple in working memory * 在工作内存中组装MinimalTuple */ tuple = ExecCopySlotMinimalTuple(slot); USEMEM(state, GetMemoryChunkSpace(tuple)); tuplestore_puttuple_common(state, (void *) tuple); MemoryContextSwitchTo(oldcxt);}

tuplestore_puttuple_common
tuplestore_puttupleslot函数的实现

static voidtuplestore_puttuple_common(Tuplestorestate *state, void *tuple){ TSReadPointer *readptr; int i; ResourceOwner oldowner; state->tuples++; switch (state->status) { case TSS_INMEM: /* * Update read pointers as needed; see API spec above. * 需要时更新读指针 */ readptr = state->readptrs; for (i = 0; i < state->readptrcount; readptr++, i++) { if (readptr->eof_reached && i != state->activeptr) { //已达末尾,且指针非活动,则设置相应的状态和位置 readptr->eof_reached = false; readptr->current = state->memtupcount; } } /* * Grow the array as needed. Note that we try to grow the array * when there is still one free slot remaining --- if we fail, * there'll still be room to store the incoming tuple, and then * we'll switch to tape-based operation. * 需要时扩展数组大小. * 注意:在仍有一个空闲slot剩余时尝试增大数组,如果失败仍有空间存储进入的元组, * 然后切换至tape-based操作. */ if (state->memtupcount >= state->memtupsize - 1) { (void) grow_memtuples(state); Assert(state->memtupcount < state->memtupsize); } /* Stash the tuple in the in-memory array */ //指向tuple state->memtuples[state->memtupcount++] = tuple; /* * Done if we still fit in available memory and have array slots. * 仍有可用内存并有数组slots,已完成所有工作,可返回. */ if (state->memtupcount < state->memtupsize && !LACKMEM(state)) return; //否则的话,需要落盘 /* * Nope; time to switch to tape-based operation. Make sure that * the temp file(s) are created in suitable temp tablespaces. * 切换至tape-base操作. * 确保临时文件在合适的temp表空间中创建. */ PrepareTempTablespaces(); /* associate the file with the store's resource owner */ //关联文件与存储资源宿主 oldowner = CurrentResourceOwner; CurrentResourceOwner = state->resowner; state->myfile = BufFileCreateTemp(state->interXact); CurrentResourceOwner = oldowner; /* * Freeze the decision about whether trailing length words will be * used. We can't change this choice once data is on tape, even * though callers might drop the requirement. * 关于是否使用结尾长度字需要"冻结"此决定. * 一旦数据落盘就不能改变此选择,即使调用者可能会放弃此要求. */ state->backward = (state->eflags & EXEC_FLAG_BACKWARD) != 0; state->status = TSS_WRITEFILE; dumptuples(state); break; case TSS_WRITEFILE: /* * Update read pointers as needed; see API spec above. Note: * BufFileTell is quite cheap, so not worth trying to avoid * multiple calls. * 需要时更新读指针. * 注意:BufFileTell执行效率很高,因此不值得尝试避免循环多次调用. */ readptr = state->readptrs; for (i = 0; i < state->readptrcount; readptr++, i++) { if (readptr->eof_reached && i != state->activeptr) { readptr->eof_reached = false; BufFileTell(state->myfile, &readptr->file, &readptr->offset); } } //#define WRITETUP(state,tup) ((*(state)->writetup) (state, tup)) WRITETUP(state, tuple); break; case TSS_READFILE: /* * Switch from reading to writing. * 从读切换至写. */ if (!state->readptrs[state->activeptr].eof_reached) BufFileTell(state->myfile, &state->readptrs[state->activeptr].file, &state->readptrs[state->activeptr].offset); if (BufFileSeek(state->myfile, state->writepos_file, state->writepos_offset, SEEK_SET) != 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not seek in tuplestore temporary file: %m"))); state->status = TSS_WRITEFILE; /* * Update read pointers as needed; see API spec above. * 需要时更新读指针. */ readptr = state->readptrs; for (i = 0; i < state->readptrcount; readptr++, i++) { if (readptr->eof_reached && i != state->activeptr) { readptr->eof_reached = false; readptr->file = state->writepos_file; readptr->offset = state->writepos_offset; } } //#define WRITETUP(state,tup) ((*(state)->writetup) (state, tup)) WRITETUP(state, tuple); break; default: elog(ERROR, "invalid tuplestore state"); break; }}voidBufFileTell(BufFile *file, int *fileno, off_t *offset){ *fileno = file->curFile; *offset = file->curOffset + file->pos;}三、跟踪分析

执行SQL：

[local]:5432 pg12@testdb=# select * from tbl a where a.id not in (select b.id from t_big_null b);

启动gdb，进入断点

(gdb) b tuplestore_puttupleslotBreakpoint 1 at 0xab9134: file tuplestore.c, line 712.(gdb) cContinuing.Breakpoint 1, tuplestore_puttupleslot (state=0x1efec78, slot=0x1efd4e0) at tuplestore.c:712712 MemoryContext oldcxt = MemoryContextSwitchTo(state->context);(gdb)

输入参数

(gdb) n717 tuple = ExecCopySlotMinimalTuple(slot);(gdb) 718 USEMEM(state, GetMemoryChunkSpace(tuple));(gdb) 720 tuplestore_puttuple_common(state, (void *) tuple);(gdb) p *state$1 = {status = TSS_INMEM, eflags = 2, backward = false, interXact = false, truncated = false, availMem = 4177840, allowedMem = 4194304, tuples = 0, myfile = 0x0, context = 0x1efce00, resowner = 0x1e5d308, copytup = 0xaba7bd <copytup_heap>, writetup = 0xaba811 <writetup_heap>, readtup = 0xaba9d9 <readtup_heap>, memtuples = 0x1f18ed0, memtupdeleted = 0, memtupcount = 0, memtupsize = 2048, growmemtuples = true, readptrs = 0x1f056a0, activeptr = 0, readptrcount = 1, readptrsize = 8, writepos_file = 0, writepos_offset = 0}(gdb) p *slot$2 = {type = T_TupleTableSlot, tts_flags = 16, tts_nvalid = 0, tts_ops = 0xc3e780 <TTSOpsBufferHeapTuple>, tts_tupleDescriptor = 0x7f16f33f5378, tts_values = 0x1efd550, tts_isnull = 0x1efd558, tts_mcxt = 0x1efce00, tts_tid = {ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 1}, tts_tableOid = 49155}(gdb) p slot->tts_values[0]$3 = 0(gdb)

进入tuplestore_puttuple_common

(gdb) steptuplestore_puttuple_common (state=0x1efec78, tuple=0x1f05ce8) at tuplestore.c:771771 state->tuples++;(gdb)

当前状态TSS_INMEM

(gdb) p state->status$4 = TSS_INMEM(gdb)

如需要，更新读指针（无需更新）

(gdb) n773 switch (state->status)(gdb) 780 readptr = state->readptrs;(gdb) 781 for (i = 0; i < state->readptrcount; readptr++, i++)(gdb) p *readptr$5 = {eflags = 2, eof_reached = true, current = 0, file = 2139062143, offset = 9187201950435737471}(gdb) n783 if (readptr->eof_reached && i != state->activeptr)(gdb) p state->readptrcount$6 = 1(gdb) p state->activeptr$7 = 0(gdb) n781 for (i = 0; i < state->readptrcount; readptr++, i++)(gdb)

如需要，扩展数组（实际不需要）

(gdb) 796 if (state->memtupcount >= state->memtupsize - 1)(gdb) p state->memtupcount$8 = 0(gdb) p state->memtupsize - 1$9 = 2047(gdb) n803 state->memtuples[state->memtupcount++] = tuple;(gdb)

放入到内存中，返回

(gdb) n808 if (state->memtupcount < state->memtupsize && !LACKMEM(state))(gdb) 809 return;(gdb)

退出函数

(gdb) 892 }(gdb) tuplestore_puttupleslot (state=0x1efec78, slot=0x1efd4e0) at tuplestore.c:722722 MemoryContextSwitchTo(oldcxt);(gdb) 723 }(gdb) ExecMaterial (pstate=0x1efd1b8) at nodeMaterial.c:149149 ExecCopySlot(slot, outerslot);(gdb)

使用ignore N遍后，state->status状态变为TSS_WRITEFILE

(gdb) ignore 4 4194303Will ignore next 4194303 crossings of breakpoint 4.(gdb) cContinuing.Breakpoint 3, tuplestore_puttuple_common (state=0x160ba38, tuple=0x7f2cd90cc0b0) at tuplestore.c:771771 state->tuples++;(gdb) ...tuplestore_puttupleslot (state=0x160ba38, slot=0x160a2a0) at tuplestore.c:722722 MemoryContextSwitchTo(oldcxt);(gdb) cContinuing.Breakpoint 3, tuplestore_puttuple_common (state=0x160ba38, tuple=0x7f2cd90cc0e8) at tuplestore.c:771771 state->tuples++;(gdb) p *state$9 = {status = TSS_WRITEFILE, eflags = 2, backward = false, interXact = false, truncated = false, availMem = 3669944, allowedMem = 4194304, tuples = 4192545, myfile = 0x162ad80, context = 0x1609bc0, resowner = 0x1579170, copytup = 0xaba7bd <copytup_heap>, writetup = 0xaba811 <writetup_heap>, readtup = 0xaba9d9 <readtup_heap>, memtuples = 0x7f2cd914a050, memtupdeleted = 0, memtupcount = 0, memtupsize = 65535, growmemtuples = false, readptrs = 0x1627590, activeptr = 0, readptrcount = 1, readptrsize = 8, writepos_file = 0, writepos_offset = 0}(gdb) n773 switch (state->status)(gdb) 841 readptr = state->readptrs;(gdb) 842 for (i = 0; i < state->readptrcount; readptr++, i++)(gdb) 844 if (readptr->eof_reached && i != state->activeptr)(gdb) 842 for (i = 0; i < state->readptrcount; readptr++, i++)(gdb) 853 WRITETUP(state, tuple);(gdb) 854 break;(gdb) p *state->myfile$10 = {numFiles = 1, files = 0x7f2cd934c008, isInterXact = false, dirty = true, readOnly = false, fileset = 0x0, name = 0x0, resowner = 0x1579170, curFile = 0, curOffset = 58687488, pos = 8156, nbytes = 8156, buffer = { data = "\000\t\030\000\335\366?\000\016\000\000\000\001\000\000\t\030\000\336\366?\000\016\000\000\000\001\000\000\t\030\000\337\366?\000\016\000\000\000\001\000\000\t\030\000\340\366?\000\016\000\000\000\001\000\000\t\030\000\341\366?\000\016\000\000\000\001\000\000\t\030\000\342\366?\000\016\000\000\000\001\000\000\t\030\000\343\366?\000\016\000\000\000\001\000\000\t\030\000\344\366?\000\016\000\000\000\001\000\000\t\030\000\345\366?\000\016\000\000\000\001\000\000\t\030\000\346\366?\000\016\000\000\000\001\000\000\t\030\000\347\366?\000\016\000\000\000\001\000\000\t\030\000\350\366?\000\016\000\000\000\001\000\000\t\030\000\351\366?\000\016\000\000\000\001\000\000\t\030\000\352\366?\000\016\000\000\000\001\000\000\t\030\000"..., force_align_d = 1.7780737478550286e-307, force_align_i64 = 18004352582551808}}...

DONE

N/A