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。
typedef enum
{
TSS_INMEM,
TSS_WRITEFILE,
TSS_READFILE
} TupStoreStatus;
struct Tuplestorestate
{
TupStoreStatus status;
int eflags;
bool backward;
bool interXact;
bool truncated;
int64 availMem;
int64 allowedMem;
int64 tuples;
BufFile *myfile;
MemoryContext context;
ResourceOwner resowner;
void *(*copytup) (Tuplestorestate *state, void *tup);
void (*writetup) (Tuplestorestate *state, void *tup);
void *(*readtup) (Tuplestorestate *state, unsigned int len);
void **memtuples;
int memtupdeleted;
int memtupcount;
int memtupsize;
bool growmemtuples;
TSReadPointer *readptrs;
int activeptr;
int readptrcount;
int readptrsize;
int writepos_file;
off_t writepos_offset;
};
#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
typedef enum
{
TSS_INMEM,
TSS_WRITEFILE,
TSS_READFILE
} TupStoreStatus;
typedef struct
{
int eflags;
bool eof_reached;
int current;
int file;
off_t offset;
} 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)
#define MAX_PHYSICAL_FILESIZE 0x40000000
#define BUFFILE_SEG_SIZE (MAX_PHYSICAL_FILESIZE / BLCKSZ)
struct BufFile
{
//集合中物理文件的数量
int numFiles;
//------- 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;
//跨事务?
bool isInterXact;
//脏数据?
bool dirty;
//是否只读?
bool readOnly;
//如共享,段文件的空间大小
SharedFileSet *fileset;
//如共享,该BufFile的名称
const char *name;
ResourceOwner resowner;
//文件索引,当前位置的第(0..n)部分
int curFile;
//当前位置的偏移部分
off_t curOffset;
//buffer中的下一个R/W位置
int pos;
//buffer中的有效字节数
int nbytes;
PGAlignedBlock buffer;
};
二、源码解读
tuplestore_puttupleslot
把接收到的tuple放到tuplestore中
void
tuplestore_puttupleslot(Tuplestorestate *state,
TupleTableSlot *slot)
{
MinimalTuple tuple;
MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
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 void
tuplestore_puttuple_common(Tuplestorestate *state, void *tuple)
{
TSReadPointer *readptr;
int i;
ResourceOwner oldowner;
state->tuples++;
switch (state->status)
{
case TSS_INMEM:
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;
}
}
if (state->memtupcount >= state->memtupsize - 1)
{
(void) grow_memtuples(state);
Assert(state->memtupcount < state->memtupsize);
}
//指向tuple
state->memtuples[state->memtupcount++] = tuple;
if (state->memtupcount < state->memtupsize && !LACKMEM(state))
return;
//否则的话,需要落盘
PrepareTempTablespaces();
//关联文件与存储资源宿主
oldowner = CurrentResourceOwner;
CurrentResourceOwner = state->resowner;
state->myfile = BufFileCreateTemp(state->interXact);
CurrentResourceOwner = oldowner;
state->backward = (state->eflags & EXEC_FLAG_BACKWARD) != 0;
state->status = TSS_WRITEFILE;
dumptuples(state);
break;
case TSS_WRITEFILE:
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:
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;
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;
}
}
void
BufFileTell(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_puttupleslot
Breakpoint 1 at 0xab9134: file tuplestore.c, line 712.
(gdb) c
Continuing.
Breakpoint 1, tuplestore_puttupleslot (state=0x1efec78, slot=0x1efd4e0) at tuplestore.c:712
712 MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
(gdb)
输入参数
(gdb) n
717 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) step
tuplestore_puttuple_common (state=0x1efec78, tuple=0x1f05ce8) at tuplestore.c:771
771 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) n
773 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) n
783 if (readptr->eof_reached && i != state->activeptr)
(gdb) p state->readptrcount
$6 = 1
(gdb) p state->activeptr
$7 = 0
(gdb) n
781 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) n
803 state->memtuples[state->memtupcount++] = tuple;
(gdb)
放入到内存中，返回
(gdb) n
808 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:722
722 MemoryContextSwitchTo(oldcxt);
(gdb)
723 }
(gdb)
ExecMaterial (pstate=0x1efd1b8) at nodeMaterial.c:149
149 ExecCopySlot(slot, outerslot);
(gdb)
使用ignore N遍后，state->status状态变为TSS_WRITEFILE
(gdb) ignore 4 4194303
Will ignore next 4194303 crossings of breakpoint 4.
(gdb) c
Continuing.
Breakpoint 3, tuplestore_puttuple_common (state=0x160ba38, tuple=0x7f2cd90cc0b0) at tuplestore.c:771
771 state->tuples++;
(gdb)
...
tuplestore_puttupleslot (state=0x160ba38, slot=0x160a2a0) at tuplestore.c:722
722 MemoryContextSwitchTo(oldcxt);
(gdb) c
Continuing.
Breakpoint 3, tuplestore_puttuple_common (state=0x160ba38, tuple=0x7f2cd90cc0e8) at tuplestore.c:771
771 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) n
773 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
四、参考资料
N/A
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